Solid Earth & Near Earth Posters

We used the GOCE measurement (Gravity Field and Steady-State Ocean Circulation Explorer, 2009–2013) data sets to analyze the regional gravity anomalies and to study the underground structures in the Adamawa volcanic uplift.

The Adamawa volcanic uplift which include the Mbere Basin in central Cameroon forms the eastward termination of the Cameroon Volcanic Line (CVL) in West-Central Africa. This line is unique among intra-plate volcanic provinces in that it straddles a continental margin and has both oceanic and continental volcanic centres. The uplift is characterised by a long-wavelength negative Bouguer anomaly similar in shape and amplitude to those of other African basement uplifts.

Two gravities profiles derived from the Bouguer gravity map of Adamawa plate, perpendicular to the anomaly associated with the uplift shows a broad negative and an axial positive Bouguer anomaly. These profiles are used the logarithmic power spectrum technique to obtain detailed images and corresponding source depths as well as certain lateral inhomogeneity of structure density. The broad negative and central positive anomalies beneath the Adamawa uplift are interpreted as a consequence of lithospheric thinning (27.5 - 35 km) and crustal thinning (3.67 – 11.5 km), respectively. Compared to the Kenya dome, the Adamawa uplift may be in an early stage of continental rifting, along the site of a pre-existing basement weakness, the Central African Shear Zone (CASZ).

A comparison of gravity anomalies difference (GOCE TIM_R5 and TIM_R4) and climatological data reveal a strong link and the possible impact of hydrography and moisture on the variation of the gravity on the gap of the Mbere basin.

Our results are in good agreement with previous investigations. 

China Seismo-Electromagnetic Satellite (CSES) is the first Chinese electromagnetic satellite mission related to earthquake study. It will be launched in September of 2016, at the height of 506km with Sun-synchronous orbit. So it is expected to operate in the same time period with SWARM of 2-3 years in future, which provides a rare opportunity for validating the ionospheric detecting data at different altitude by under same near-Earth environment. On this satellite, eight scientific payloads will be installed, including High-Precision Magnetometer; Electric Field Detector, Search-Coil Magnetometer, Langmuir Probe, Plasma Analyzer, GNSS Occultation, Tri-Band Beacon, Energetic Particle Package, by which more than 20 components in electromagnetic field, in-situ plasma parameters, plasma profiles will be recorded simutaneously. Here the definition of four level data in CSES and the main parameters from different payloads will be introduced. And the key technologies are presented in data inversion and calibration, to illustrate how to obtain the final scientific products from satellite raw data, especially on the calibration between geomagnetic field vector and scalar. Finally, in order to ensure the data quality, the methods in data evaluation and validation are provided from previous and current research by using  IGRF model, DEMETER satellite in-situ data, SWARM data and other data source together. Furthermore, future cooperation is expected between China and ESA in satellite constellation and data validation techniques.

Energetic particle precipitation in Auroras (E <20 keV) produces nitric oxide (NO) in the upper meso- and lower thermosphere region (UMLT). The subsequent descent of the NO produced in the UMLT to the lower meso- and upper stratosphere is referred to as the energetic particle precipitation indirect effect (EPP IE). The downwelling of NO produced in Auroras alters the chemistry of the mesosphere and upper stratosphere (e.g. by the NOx cycle) and possibly has important effects also on its dynamics.

By observations of auroral precipitation from SSUSI(DMSP) and measurements of NO from MIPAS(ENVISAT) and SMR(ODIN) we investigate the quantitative relation between the electron fluxes and characteristic energies of auroral precipitation, the NO produced in the lower thermosphere and the subsequent downwelling of NO. Using additional ground-based (e.g. Meteor Radar, Microwave Radiometer) and satellite observations (SOFIE) we attempt to quantify the EPP IE and its impact on atmospheric chemistry and dynamics.

Today the problem of monitoring of space weather and geomagnetic field (GMF) parameters is partially solved by a number of magnetic observatories and satellite observations. All data measured and collected about geomagnetic field and space weather is distributed in various sources and storages. It is obvious that necessity in integrated information space is very acute. Development of such integrated information space will provide a possibility to get any data about space weather and geomagnetic field at any point of the Earth’s surface at any moment of time.

The obvious way to solve the problem is to implement innovative information technologies there. In particular the most expectations are about using web technologies and geoinformation systems to solve the problem.  

Today one of the possible solutions of the problem is a geographical web-portal GEOMAGNET (http://geomagnet.ru/index-en.html).  GEOMAGNET Project is initiated and performed by scientists, engineers and programmers with support of IZMIRAN and The Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences (IPE RAS).

GEOMAGNET includes four services providing observation, analysis, three-dimensional visualization and calculation of parameters of geomagnetic field and space weather, which are measured by both astronomical and geophysical observatories and satellite observations:

– "Ground Monitoring of GMF Parameters" provides registration and visualization of partial observations of the geomagnetic field and magnetic observatories data with a high density distribution over the surface of the Earth.

– "Solar Activity: Monitoring and Analysis" allows users to monitor solar weather in real time (on the basis of satellite observations) and carry out a comprehensive analysis of its parameters, to assess how their values change for different periods of time (from one hour to several days). Data analysis is also available in amplitude and frequency mode by single or groups of parameters of space weather.

– "Space Monitoring of GMF Parameters" is a powerful tool for monitoring, analysis and three-dimensional representation of the geomagnetic field parameters. Data is obtained from satellite observations in real time mode. A user can choose single or group of parameters and visualize them on globe with both histograms and isolines, generated according to data in KML format.

– "Geomagnetic Calculator (WMM2015)" is a Web-based application providing calculation parameters of geomagnetic field and secular variations according to the set of coordinates and dates. A user of any level can calculate and analyze parameters of geomagnetic field at his current location or at any other point on the Earth. A unique feature of the service is a calculation of parameters of geomagnetic field on the basis of elevation data, which is obtained automatically.

GEOMAGNET includes a set of mobile applications: "Ground Monitoring App", "Solar Activity App", "Intellection Test Module App", "Magnetic Error Calculator App" and others. The applications provide collection and transmition of data about magnetic state parameters. Today the applications are widely used by specialists in geophysics, medicine, metrology and many other areas (about several thousand downloads all around the world). 

The European Space Agency contributes to information technology developments for satellite data access and analysis. In the technology research project “Virtual Workspaces for Earth Observation Scientists” the Agency focused on the particular characteristics of the Swarm mission. A collaboration of scientists and industry delivered the presented Prototype system.

Traditionally scientists operate their own computing facilities into which they download the satellite data for performing their specialized tasks. The Prototype demonstrates augmentations and simplifications for this process by providing:

Interactive tools with particularly convenient properties supporting the data selection, visualisation, scientific analysis and documentation

Services in the cloud which make satellite data access easier and support on-demand generation of derived value-added information

The included features for Swarm mission data access, visualisation, and analysis are:

Graphical Web Interface supporting interactive virtual globe and rich analytical toolset

Plotting Swarm Level 1b data (such as Magnetic field vector , Magnetic field intensity) as a function of (co-)latitude/time

Visualisation of magnetic field residuals with the possibility of selecting different provided field models and the option of uploading the users own model as spherical harmonics coefficients

Visualisation of the magnetic field intensity maps (calculated on-the-fly based on selected model, time and altitude)

Magnetic field intensity difference between two satellites

Horizontal magnetic field residuals

Magnetic field gradient maps

Magnetic field intensity along field lines (Three-dimensional)

Vector and scalar plots along multiple orbits

The ESA Earth Observation Magnetic Mission Swarm carries high precision vector and scalar magnetometers. Careful analyses have revealed s smaller, Sun driven magnetic disturbance of the vector magnetometer. This disturbance have been imperically mapped and corrected since mid 2015. This work will show the recent developments in the modelling of this disturbance.

In the framework of the ESA Earth Observation Magnetic Mapping Mission Swarm, the Expert Support Laboratories (ESL) provides high quality Level 2 Products describing a.o. the magnetic fields of the Earth. This poster provides details of the Level 2 Products from the Comprehensive Inversion chain comprising models of the magnetic fields of Earth's core and lithosphere, ionosphere and magnetosphere.

Gravity field information imposes valuable constraints for modelling the density structure of the lithosphere. In this respect, passive continental margins play an important role, regarding their specific features related to density distribution and isostatic behavior.

In this contribution we put the focus on the region of the South Atlantic Ocean and its margins. Based on this test area, it is intended to evaluate the contribution of GOCE (and GRACE) gravity field information for density modelling and improved interdisciplinary interpretation. The spatial resolution to perform these tasks shall be quantified, and it shall be evaluated to what extent satellite information alone, which is always limited in spatial resolution due to signal attenuation with altitude, is sufficient. Further, the added value of adding complementary data is investigated. It shall also be discussed in which way 3D gravity gradient information, as it was measured by GOCE for the very first time, can help for the interpretation. Additionally, the contribution of (satellite) gravity information as data source that is complementary to 3D seismic tomography and magnetic field data to combined modelling of lithospheric structures shall be assessed.

Finally, based on the conclusions derived from this study the geophysical user needs, from the perspective of lithospheric modelling, for a next generation gravity field mission shall be derived.

We present sensitivity tests based on a synthetic model of the Fennoscandian lithosphere in order to validate the effect of induced and remanent magnetization in magnetic data at the height of satellites and airborne surveys. The use of airborne data and satellite data is complementary as they are due to their different height sensitive to different depth domains. Our analysis is based on a surface discretization by tesseroids.

As an example of our approach we present a synthetic model based on the geometry of lithospheric density models derived from GOCE gravity satellite mission and petrophysical maps of Fennoscandia (susceptibility and total magnetization) and show magnetization (induced and remanent) in deep crustal layers affects the magnetic field over the area.

Petrophysical data are applied to update our model for lateral varying magnetization in the upper crust. This additional constraint helped to evaluate and to quantify the effect from shallow sources in observed magnetic field on satellite height and supported a better differentiation of anomalies from deeper sources. We subsequently tested the data sensitivity of the middle and lower crust and simulated the effect of different scenarios for petrophysical variations with different properties in the lower crust. The strong magnetization of the oceanic plate locally superimposes the magnetic field generated by the Fennoscandian shield at satellite height. To estimate this effect, we employed oceanic lithosphere age maps to include more realistic magnetization for the oceanic crust.  

Furthermore, we explore the characteristic of the Curie isotherm, limiting the thickness of the magnetic lithosphere. Estimations of the Curie isotherm based on the temperature model of the lithosphere are used to modify the synthetic model and compare the calculated field with the observed one.

Finally, we applied a time-varying core field to our model to see how the magnetic field and the magnetic field gradients on the satellite height reflect the changes in induced magnetization over the large time period in respect to the areas with remanent magnetization.

Our study addresses the thermal and compositional structure of the Antarctic lithosphere by combing gravity (gradients), seismological and petrological models in a forward and inverse manner. Hereby, we discuss both the interplay of the deeper lithospheric architecture with bedrock topography and ice dynamics as its dynamic relation with GIA.

Antarctica is still an underexplored part of the Earth with respect to geophysical data coverage. Despite recent large scale international campaigns, which have for example acquired a wealth of airborne gravity and magnetic datasets, knowledge of the crustal and lithospheric structure of the continent is limited, as the massive ice sheets that cover Antarctica hamper direct sampling and the seismic data coverage is still sparse.

Considerable efforts have been made in recent years to improve the knowledge of the bedrock beneath Antarctica. However, it is estimated that available bedrock compilations have in some regions still uncertainties larger than 1 km. If these uncertainties are present where the bedrock is beneath sea level or bordering the ocean, they can have a large impact on calculations of ice sheet dynamics/stability; this is e.g. the case in interior East Antarctica regions.

We will evaluate these models using gravity gradients and establish a state-of-the-art lithospheric model, that combines seismological upper mantle models and petrological concepts with respect to temperature and composition in the upper mantle. With a reasonable range of rock parameters from such analysis, we can as well improve GIA models. A further target for improvement of the GIA models is the inclusion of loading changes in the recent past (i.e. the last centuries) that is not included in standard ice models. The recent changes can have large consequences on GIA predictions and our study will provide the first sensitivity studies for recent loading with 3D viscosity values.

In the framework of the ESA GOCE+ projects, thermosphere densities and crosswind speeds were retrieved from GOCE observations for the entire Science Mission from November 2009-20 October 2013. The most recent version of the DTM thermosphere models, DTM2013, is constructed with GOCE density data up to May 2012 as well as with GRACE, CHAMP and historical density data. The added value of the unique GOCE density dataset will be demonstrated by means of comparisons to the COSPAR reference models JB2008, NRLMSISE-00 and DTM. The standard deviation of the DTM2013 density ratios (Observed/Modeled density) is just below 10%, which is a very good result. Rather serious model errors are revealed for the models that did not assimilate GOCE data.

A new ESA General Study (PREGO) focuses on the last three weeks of the mission. The ion propulsion was no longer operating after 20 October and GOCE re-entered the atmosphere over the Falkland Islands on 11 November 2013. The altitude decay rate was very high, but the accelerometers continued to operate up to 8 November, and the GPS receiver up to a day before re-entry. First results of thermosphere model performance for this last part of the GOCE mission will be presented, as well as a first analysis of the observed atmospheric variability. 

The Multiple Input / Multiple Output System Theory is used in the spectral combination of marine and satellite data for Quasi-stationary SST estimation. 15 years (2000 – 2015) of altimetric data from ERS2, ENVISAT, SARAL and HY2 satellites are combined optimally with in situ marine gravity observations. The repeated character of the altimetric missions provides more than one sample of Sea Surface Height (SSH) data sets, and the approximation of the input signal and output error power spectral densities is feasible using this successive information. The assimilation of low frequency global gravity information from GOCE/GRACE satellites is considered in data reductions. The geophysical active area of the Eastern Mediterranean Sea is chosen as test area and the evolution of yearly SST is presented.

A new synthetic model of the time-variable global gravity field is now available based on realistic mass variability in atmosphere, oceans, terrestrial water storage, continental ice-sheets, and the solid Earth. It is provided in Stokes coefficients up to degree and order 180 with a temporal resolution of 6 h covering the time period 1995–2006, and can be readily applied as a source model in future gravity mission simulation studies. The model contains plausible variability and trends in both low-degree coefficients and the global mean barystatic sea level. It depicts reasonable mass variability all over the globe at a wide range of frequencies including multi-year trends, year-to-year variability, and seasonal variability even at very fine spatial scales, which is important for a realistic representation of spatial aliasing and leakage. In particular on these small spatial scales between 50 and 250 km, the model contains a range of signals that have not been reliably observed yet by satellite gravimetry. In addition, the model provides substantial high-frequency variability at periods down to a few hours only, thereby allowing to critically test strategies for the minimization of temporal aliasing.

It is known, some analytical models of a geomagnetic field consist of up to 720 spectral harmonics. It is obvious, satellite magnetic surveys do not allow to measure signals in a range of 200-720 spectral harmonics. But it is possible for magnetic surveys at sub-satellite (aeromagnetic and balloon) altitudes (H=0-40 km). Having such balloon gradient magnetic data, we have made estimations of a lithospheric geomagnetic field along a trajectory of flight of a balloon (March 2013, Н=30 km). The investigated trajectory passed in area of arrangement the Kama-Embensk magnetic anomaly (Volga River - Southern Urals Mountains). Along the same trajectory, the estimations of lithospheric geomagnetic field obtained by ground-based (Makarova Z.A. (editor-in chief) (1974). "The Map of Anomalous Magnetic Field of the U.S.S.R", H=0 km) and satellite (model MF-7, H=400 km) data have been created. Mentioned above three profiles of lithospheric geomagnetic field have been compared. In particular, comparisons the ground-based and the balloon profiles have been executed by means of the wavelet analysis. The analysis has shown - the spectrum of ground-based profile data contains harmonics which lengths of waves do not exceed 130 km (this conclusion can be distributed on total Makarova's Map) and the spectrum of balloon profile data contains the harmonic with lengths of up to 500 km. The site of magnetic anomaly on balloon profile precisely coincides with a site of a maximum of intensity Kama-Embensk lithospheric magnetic anomaly on satellite data profile. This fact (both anomalies are "equal" in two data sets) allows us to conclude – ground-based (aeromagnetic) data do not allow to identify magnetic anomalies of lithospheric field with characteristic lengths more than 130 km. Comparison of the balloon and the ЕММ/720 model (this model have been constructed on the basis of satellite and ground-based data and developed up to 720-th spherical harmonics) profiles of the lithospheric field has shown - their distinctions reach up to 50 %. We conclude - for estimations of quality of modelling of the lithospheric magnetic field of the Earth by analytical models it is necessary to use the balloon gradient magnetic survey data.

Ocean tide aliasing is currently one of the main limiting factors for temporal gravity field determination and the derivation of mass transport processes in the Earth system. This will be true even more for future gravity field missions with improved measurement technology, which cannot be fully exploited due to this dominant systematic error source. In several previous studies it has been shown that temporal aliasing, related to tidal and non-tidal sources, can be significantly reduced by double-pair formations, e.g., in a so-called Bender configuration, and its effects can be migrated to higher frequencies by an optimum orbit choice, especially the orbit altitude (Murböck et al. 2014). Improved processing strategies and extended parameter models should be able to further reduce the problem. Concerning non-tidal aliasing, it could be shown that the parameterization of short-period long-wavelength gravity field signals, the so-called Wiese approach, is a powerful method for aliasing reduction (Wiese et al. 2011), but it does not really work for the very short-period signals of ocean tides with mainly semi-diurnal and diurnal periods (Daras 2015).

In this contribution, several methods dealing with the reduction of ocean tide aliasing are investigated both from a methodological and a numerical point of view. One of the promising strategies is the co-estimation of selected tidal constituents over long time periods, also considering the basic orbit frequencies of the satellites. These improved estimates for ocean tide signals can then be used in a second step as an enhanced de-aliasing product for the computation of short-period temporal gravity fields.

From a number of theoretical considerations and numerical case-studies, recommendations for an optimum orbit selection with respect to reduction of ocean tide aliasing shall be derived for two main mission scenarios. The first one is a classical Bender configuration being composed of a (near-)polar and an inclined in-line satellite pair. The second one follows the so-called GETRIS concept, assuming a high-precision inter-satellite link between high-flying GEO and/or GNSS satellites and an ensemble of low Earth orbiters (LEOs).

As a further aspect of this work, possible correlations between a dedicated ocean tide co-parameterization with other parameters (Wiese, empirical accelerations, etc.) and their impact on the gravity solution shall be analysed in detail.

In this study we investigated the scale sizes of equatorial plasma irregularities (EPIs) using measurements from the Swarm spacecraft constellation during its early and final configuration phases. Our observations show small scale sizes of EPIs (below about 55 km) in the zonal direction. For spacecraft zonal separation of about 150 km, comparably larger irregularities scale sizes are found in the early night time sector (1900-2100 LT). Clearly better correlation results were obtained in the northern hemisphere than in the southern hemisphere, implying more fragmented irregularities in the south. The inverted-C structure of EPIs is generally confirmed by the Swarm observations, but with various tilt angles and hemispherically asymmetric.

When the ion propulsion of GOCE stopped operating after October 21, 2013, the satellite experienced a rapid decay of orbital altitude. Despite the increasing airdrag conditions, GOCE accelerometers and GPS receivers delivered high-quality data until November 8 and November 10, respectively, before GOCE finally desintegrated on November 11 over the Falkland islands.

In the frame of a new ESA General Study Program (PREGO) the data provided by GOCE during its re-entry phase shall be exploited to improve the capacities on re-entry predicition. The study is conducted by Deimos Space, Madrid as tenderer and the Astronomical Institute of the University of Bern (AIUB) as well as the Centre National d'Etudes Spatiales (CNES), Toulouse as subcontractors.

The AIUB will provide the GPS-based GOCE precise kinematic and reduced-dynamic orbits which shall be used as reference trajectories for the investigations of the study. Focusing on the last three weeks of GOCE, we revisit the GOCE precise orbit determination as conducted by AIUB in the frame of the GOCE High-Level Processing Facility (HPF), which provided the official GOCE precise science orbits. While the reduced-dynamic GOCE precise science orbits were computed by making extensive use of optimized pseudo-stochastic accelerations, a more physical modeling of air-drag is crucial to obtain highest-quality GOCE orbits towards the end of the re-entry phase. In addition to empirical accelerations, state-of-the-art atmospheric density models like NRLMSISE-00 or DTM2013 will be used to model air-drag and to provide more dynamic reference trajoctories suitable for extrapolation. Apart from external SLR validation, the new GOCE reduced-dynamic orbits will be validated by comparing them to the kinematic orbits and by comparing the modeled and empirical accelerations with the measurements of the on-board accelerometers.

The compact spacecraft payload SATRAM, operating in LEO orbit since 2013 on board the Proba-V satellite from ESA, provides comprehensive and high resolution radiation monitoring in the satellite environment. Equipped with the hybrid semiconductor pixel detector Timepix, the technology demonstration payload determines the composition and spectral characterization of the mixed radiation field with quantum imaging sensitivity, charged particle tracking, energy loss and directionality capability. With a polar orbit (sun synchronous, 98° inclination) and altitude of 820 km the space radiation field is visualized and continuously sampled essentially over the entire planet. In this contribution we present the resulting spatial and time distributions of dose rates and particle fluxes produced in wide dynamic range.

Acknowledgments: Design and construction of the SATRAM/Timepix spacecraft payload was funded by ESA grant 4000105089/11/NL/CBi. Research carried out in frame of the Medipix Collaboration. Acknowledgments are due to former team members (Z. Vykydal, D. Turecek (IEAP CTU Prague), Z. Kozacek, P. Vana, J. Mares, M. Simcak, Z. Dvorak (CSRC)) and to P. Nieminen (ESA ESTEC) for discussions and suggestions.

The density structure of the lithosphere is of key interest for a better understanding of its geodynamic evolution. Gravity gradient data, measured in the course of ESA´s GOCE satellite mission, are sensitive to geometry and density variations of the main lithospheric layers, i.e. ice and sediment thickness, the Moho depth and the temperature and composition of the upper mantle. We illustrate this with case examples of the Tornquist Zone in South-Scandinavia, where cratonic Baltica amalgamated with the terrane Avalonia, and the Antarctic continent, for which its lithospheric structure is still poorly known. We show results of initial sensitivity analyses for the gravity gradients with respect to different Moho geometry and density contrast. In the second step, we demonstrate the effect of different compositions and thicknesses of the lithospheric upper mantle on gravity gradients at satellite height. Our model setup is based on seismic tomography and we discuss the link between upper mantle petrology, density and seismic velocity.

Downward continuation of the potential data is useful tool for manipulating and interpreting satellite gravity data near the generating sources. Several methods and strategies have been proposed for the downward continuation of the satellite gravity data. This contribution investigates regional recovery of the second radial derivative of the disturbing gravitational potential at the mean sphere in the area of Europe from the same quantity measured by satellite GOCE. A special attention is paid to far zone effects, which are estimated with three approaches. In the first approach, which will be a reference, we use a full (near global) coverage of GOCE-based measurements. In the second approach, the integral formula is rigorously decomposed into two parts, i.e., the effects of the second radial derivative of the disturbing gravitational potential within near and distant zones. While the effect of the near zone is sought as an inverse problem, the effect of the distant zone is synthesized from the global gravitational model GGM05S using spectral weights given by truncation error coefficients. In the third approach the effect of far zones is computed by the numerical integration with the same global gravitational model as in the previous approach. The process of the downward continuation is stabilized by the Tikhonov regularization. Estimated values of the radial-radial component of the disturbing gravitational tensor are compared with those that are synthesized directly from EGM2008.       

The gravity gradients observed from GOCE are particularly sensitive to the density and geometry of the Earth’s interior structures. As our planet, in a first spherical approximation, consists of layers of varying density and width, there is a different effect from each  layer to the total gravity gradient signal, as this is measured by the satellite. In this paper, we  attempt to isolate the gravity gradient radial component Vr of the various layers (crust, lithosphere, mantle and core) and investigate the effect of each of these layers to the measured gravimetric signal. The selected test area is the region  stretching over Greece (between 19 to 29 degrees longitude and 34 to 43 degrees latitude).

In order to do that, we  model each layer approximating it as a spherical shell with constant  density and width. Using this approach, we can calculate analytically the radial component of the gravity gradient  induced by each layer and compare it with the corresponding  quantity obtained as observable from GOCE at a mean satellite altitude (250km). Values for the density and width of the layers are taken from current global digital databases as well as other available information  concerning the Earth structure. Especially, we focus on the effect of crust and lithosphere, using the densities and geometry of CRUST 1.0 and LITHO 1.0 global models. The GOCE gradient grid at mean satellite altitude was created using two years (2012-2013) of GOCE gradient data (EGG_NOM_2). These data where filtered with a Butterworth filter inside the Measurement Bandwidth (5mHz – 0.05Hz) while their long wavelength signal was replaced by the corresponding part of  the combined GOCE/GRACE geopotential model GOGRA04S. 

GOCE gravity gradient data are used together with published seismic data to determine the Moho geometry and the isostatic state of the Central Asian Orogenic Belt (CAOB). The CAOB is an accretionary orogen formed during the Palaeozoic at the periphery of the Siberian cratonic nucleus by the successive amalgamation of different types of crust (cratonic, oceanic, passive margin, magmatic arc, back-arc, ophiolites, accretionary wedge) followed by an oroclinal bending during Permian-Triassic times. This large area was and is still of great interest for geoscientific studies mainly because of its potential in mineral and fossil resources and also for its outstanding, but still misunderstood, geodynamic evolution. However, the geophysical investigations remain scarce due to the remoteness of the area. A systematic analysis of the crustal thickness has been omitted yet, although the geometry of the crust-mantle boundary (Moho boundary) provides crucial information on the evolution of the lithosphere and on the coupling between upper mantle and the crust – particularly interesting for oroclinal bending processes.

In this study, the gravity gradient data set of GOCE are used to investigate the topography of the Moho for Mongolia and its surroundings, using inversion of gravity data and calculation of the isostatic Moho from topographic data. In addition, we implemented the same process to the EGM2008 satellite-terrestrial model of the Earth’s gravity anomalies and these results are compared together with those obtained for the GOCE gravity data. The results of the gravity inversion are constrained by the few xenolith studies and the seismic data available: the receiver function seismic method for north and central Mongolia, deep seismic sounding and seismic reflection profiles in northern China; and tomography in southern Siberia. Then, the effects of isostatic compensation are evaluated by the comparison between the results of the gravity inversion and the isostatic Moho. Finally, a 3D forward modelling of the gravity gradients is performed over the key parts of the CAOB. These results provide new insights into the possible tectonic scenarios and point out inconsistencies for the Altai mountain range between the conclusions leading by geological studies and our model, which indicate that unusual tectonic processes may have occurred at the upper mantle and lower crustal levels. 

Geomagnetic field variations measured on the ground and in space can be used to recover electric conductivity distribution in the mantle. Such a recovery requires solution of an inverse problem. Usually this problem is tackled by means of deterministic approach. In this work, we present an alternative approach to solve inverse problem, namely state-of-the-art stochastic optimization technique called Covariance Matrix Adaptation Evolution Strategy (CMAES). In contrast to deterministic approach, it can be considered as a global method and applied to non-smooth and non-convex functions. In addition, as it was shown recently, CMAES is well suited for quantifying inverse solution uncertainty, especially for the problems with large number of unknowns. By using the Swarm and ground-based geomagnetic data, we apply the CMAES to recover mantle conductivity model in the presence of nonuniform oceans and continents. Additionally, we employ random sampling in order to quantify uncertainty of the recovered model.

Extended abstract

The earth resources exploration and tectonic studies are promising research areas using state-of-the-art high resolution satellite gravity data and latest edge enhancement techniques (Abdul Fattah et al. 2013; Pal and Majumdar 2012a, 2012b, 2014; Pal et al. 2014, Pal and Majumdar 2014; Vaish and Pal 2014). Satellite gravity data would be utilized as an economical and quick reconnaissance tool for assessment of subsurface geological structures of remote and wide Indian Ocean regions. A number of recent global gravity models (EGM2008, EIGEN6C4) generated by assimilation of  GOCE, GRACE, and LAGEOS (Laser GEOdynamics Satellite) satellite tracking data with ancillary terrestrial data and altimetry data (Braitenberg and Ebbing, 2009; Braitenberg et al., 2011; Pavlis et al. 2012; Forste et al., 2008, 2013) are available for better understanding of Earth’s geological and geodynamical processes. These new global gravity models have high accuracy and spatial resolution which could be used for delineation of structural features. They offer new possibilities to reveal the structures over the Bengal offshore regions. The gradients of potential field are the most effective techniques for delineation of geological structures/boundaries. The geological structures/edges in potential field data are assumed to be consequences from prominent discontinuities or boundaries among contrasting materials or intrusive contacts. The lineament mapping and their analysis from potential data is an important approach for regional structural and tectonic studies. The surface expression of geological structures, such as fractures (fault and joints), shear zone and foliation can be shown in the form of lineaments. The edge enhancement techniques provide crucial tool for lineament analysis in the offshore region where the rock units are well exposed. In the present study, GOCE and EIGEN6C4 gravity data have been utilized for delineation of structural features over the Indian offshore regions.

Generated High resolution gravity data have been enhanced using First and Second Vertical Derivative techniques and a no. of structural features have been delineated both in the western and the eastern offshore, from the enhanced anomaly maps. Rose diagrams have been generated from the lineament maps for structural mapping and tectonic studies over the Indian offshore regions. 

**Abstract to be presented/published in the Proc. ESA LPS 2016 WORKSHOP, Czech Republic, 9-13 May 2016.

References:

Abdul Fattah  R, Meekes  JAC, Colella  S, Bouman  J, Schmidt  M,  Ebbing  J.  2013. The application of GOCE satellite gravity data for basin and petroleum system modeling: a case-study from the Arabian Peninsula. Search and Discovery Article #120130 (2013), Posted March 13, 2013.

Braitenberg, C., Ebbing, J., 2009. New insights into the basement structure of the west-Siberian basin from forward and inverse modelling of GRACE satellite gravity data. J. Geophys. Res., 114, Bo6402,doi:10.1029/2008JB005799.

Braitenberg, C., Mariani, P., Ebbing, J., Sprlak, M., 2011. The enigmaticChadlineament revisited with global gravity and gravity gradient fields.  The Geological Society, London Special Publication, No. 357, pp.329-341.

Förste, C., Flechtner, F., Schmidt, R., Stubenvoll, R., Rothacher, M., Kusche, J., Neumayer, H., Biancale, R., Lemoine, J. M., Barthelmes, F., Bruinsma, S., Koenig, R., Meyer, U., 2008. EIGEN-GL05C - A new global combined high-resolution GRACE-based gravity field model of the GFZ-GRGS cooperation. Geophysical Research Abstracts, V. 10, EGU2008-A-03426, 2008 S Ref-ID: 1607-7962/gra/EGU2008-A-03426.

Förste, C.,  Bruinsma, S., Flechtner, F., Marty; J. C., Dahle, C., Abrykosov, O.,  Lemoine, J.M.,  Neumayer, H., Barthelmes, F.,  Biancale, R.,  König, R., 2013. EIGEN-6C2 - A new combined global gravity field model including GOCE data up to degree and order 1949 of GFZ Potsdam and GRGS Toulouse. Geophysical Research Abstracts, V. 15, EGU2013-4077-1, 2013, EGU General Assembly 2013. http://icgem.gfz-potsdam.de

Pal SK, Majumdar TJ. 2012a. Geological appraisal of the 85^oE Ridge, Bay of Bengal using GRACE and GOCE anomaly. First International GOCE Solid Earth Workshop, University of Twente, Netherlands, 16-17 October 2012, 33-34.

Pal SK, Majumdar TJ. 2012b. Utilization of GRACE gravity data for geological interpretation over a part of the Singhbhum Shear Zone.  49^th  Annual Convention on    “Towards the energy security - exploration, exploitation and new strategies”, Indian Geophysical Union, 29 - 31 October, 2012, Gandhinagar.

Pal SK,   Kumar U, Majumdar TJ. 2014. Utilization of High resolution GOCE gravity data for mapping of gravity field and structures Western offshore, India. 5th International GOCE User Workshop, 25-28 November 2014, UNESCO, Paris, France.

Pal SK, Majumdar TJ. 2014. Geological appraisal over the Singhbhum-Orissa Craton, India using GOCE, EIGEN6-C2 and in-situ gravity data. Int  J Appl  Earth Obs  and Geoinform. 10.1016/j.jag.2014.06.007.

Pavlis  NK, Holmes SA, Kenyon SC,  Factor  JK. 2012. The development and evaluation of the Earth Gravitational Model 2008 (EGM2008). J Geophys Res. 117, B04406, doi:10.1029/2011JB008916.

This presentation provides an overview of the current data production and availability. It then highlights key data quality aspects and the related processors developments. The paper also presents an outlook on the data product evolution plans and the future incorporation of additional Swarm products.

For the determination of temporal gravity fields satellite missions such as GRACE (Gravity Recovery and Climate Experiment) or CHAMP (Challenging Minisatellite Payload) were used in the last decade. These missions improved the knowledge of atmospheric, oceanic and tidal mass variations. The most limiting factor of temporal gravity retrieval quality is temporal aliasing due to the undersampling of high frequency signals, especially in the atmosphere and oceans. This kind of error causes the typical stripes in spatial representations of global gravity fields such as from GRACE.

As part of the GETRIS (Geodesy and Time Reference in Space) mission, that aims to establish a geodetic reference station and precise time- and frequency reference in space by using optical two-way communication links between geostationary (GEO) and low Earth orbiting (LEO) satellites, a possible future gravity field mission can be set up. By expanding the GETRIS space segment to the global satellite navigation systems (GNSS) the optical two-way links also connect the GALILEO satellites among themselves and to LEO satellites. From these links between GALILEO and LEO satellites gravitational information can be extracted.

In our simulations inter-satellite links between GALILEO and LEO satellites are used to determine temporal changes in the Earth’s gravitational field. One of the main goals of this work is to find a suitable constellation together with the best analysis method to reduce temporal aliasing errors. Concerning non-tidal aliasing, it could be shown that the co-estimation of short-period long-wavelength gravity field signals, the so-called Wiese approach, is a powerful method for aliasing reduction (Wiese et al. 2013). By means of a closed loop mission simulator using inter-satellite observations as acceleration differences along the line-of-sight, different mission scenarios for GALILEO-LEO inter-satellite links and different functional models like the Wiese approach are analysed.

In this presentation we compare the results of ULF wave studies using magnetic field data from the Swarm and CHAMP low-Earth-orbit (LEO) satellite missions. The low orbits are rather special for ULF wave studies, being roughly similar distances above the ionosphere as ground stations are below the ionosphere.  This provides a unique opportunity to study ULF waves and the effects of the ionosphere on their propagation by utilizing the LEO satellite data in combination with ground-based data.

The high quality magnetic field measurements from CHAMP enabled the first clearly resolved observations of Pi2 and Pc3 pulsations in LEO magnetometer data at low and middle latitudes. Comparative studies of these pulsation types observed at LEO above the ionosphere and at ground stations below the ionosphere facilitated studies of the wave nature and structure of these pulsations.

The magnetic field data from ESA's three Swarm satellites are providing added impetus to these studies of ULF waves. As a result of the orbital parameters, the satellites drift slowly in magnetic local time (MLT) with an increasing separation between Swarm B relative to A and C; this provides the possibility of global mapping of ULF wave phenomena. In addition, spatial and temporal variations should be distinguishable due to the multi-platform observations.

In this presentation, we provide a selection and comparison of ULF wave events that have been studied using Swarm and CHAMP magnetic field data.

The equatorial electrojet (EEJ) is a narrow belt of prominent electric current in the dayside E-region ionosphere. This current which isassociated with tidal wind, polarization electric field and the equatorial horizontal magnetic field represents an enhancement of the diurnal variation in the ground geomagnetic field near the magnetic dip equator. A study of the EEJ by using new observations is of great importance for further understanding the ionospheric wind dynamo and electrodynamic process. Thanks to the Absolute Scalar Magnetometer (ASM) and Vector Field Magnetometer (VFM) on board Swarm, high quality magnetic field observations have been obtained, which can be used to determine the EEJ. By using the EEJ current densities determined from the Swarm satellite constellation, the characteristics of the EEJ have been investigated. Here we are focusing on the tidal modulation of the EEJ by atmospheric tides. Of particular interest are the longitudinal gradients of the tidal signals. These gradients show a day-to-day variability that has not been studied in details.

The Mediterranean Sea has always been a lab for geosciences, given its geodynamic peculiarities, the large short-scale variations of the gravity field and the complex circulation. Within the GEOMED 2 project, new improved representations of the Mediterranean marine geoid have been deemed as necessary, so that the Mean Dynamic sea surface Topography (MDT) and the circulation can be modelled with higher accuracy and resolution. This is possible given the availability of gravity-field related satellite data from GOCE, improved models of the land topography and bathymetry and the compilation of a Mediterranean-wide gravity database. The data employed within GEOMED 2 for the determination of the marine geoid are land and marine gravity data, GOCE/GRACE based Global Geopotential Models and a combination of MISTRAL and SRTM/bathymetry terrain models. The processing methodology will be based on the well-known remove-compute-restore method following both stochastic and spectral methods for the determination of the geoid. Classic least-squares collocation (LSC) with errors has been employed investigating both spherical and planar analytical covariance functions models, while fast Fourier transform (FFT)-based techniques have provided the geoid estimation in the frequency domain. In this work, the pre-processing steps consisting in merging and validating all the available gravity observations for the wider Mediterranean are presented and discussed. Furthermore, the latest basin-wide geoid models are estimated from the validated gravity data using all outlined methodologies. The so-determined geoid models are validated against GPS/Levelling observations over land areas, with special emphasis on the coastal to near-coastal regions, as well as satellite altimetry observations from the Jason2, Envisat and Cryosat2 missions.

In October 2013 the GOCE successfully completed its mission and delivered a unique data set of gravitational gradients of the Earth gravity field. In July 2014 the 5th release of the GOCE gravity field models were made available, which are based on the complete mission data set. The paper provides an overview about what has been achieved in terms of geoid signal content and quantifies its error by comparison with independent data.

Achieving a high resolution marine gravity field is essential for the derivation of bathymetry, exploring the ocean tectonics, and practically, safe navigation of ships in the poorly surveyed regions. The accuracy of marine gravity can be improved by the improved altimeter range and dense track coverage. With the launch of CryoSat-2 in 2010, the altimeter range precision is improved by the synthetic aperture radar (SAR) mode. The tracks also cover up to higher latitudes (88°), providing dense spatial coverage in the polar regions. The gravity signal can be recovered from the along track surface slopes (gradients). The accuracy of the recovered gravity signal is dominated by the accuracy of range precision. Therefore, an optimum retracker for the derivation of accurate sea surface height (SSH) estimate should be identified at the first step.

In this paper, we will first wok on adapting the SAMOSA retracker to optimally fit to the SAR waveforms in the Arctic by additional amplitude fitting. Then, we use the 20 Hz L1c release of the CryoSat-2 products to estimate the SSH and further derive the sea surface height variations to recover the marine gravity. Precision analysis will also carried out to several empirical retrackers to compare the performance of the retrackers. Additionally, the high burst rate and high pulse repetition frequency in the SAR mode also enabled higher along track sampling through post-processing, e.g., 80 Hz posting rate on the surface. We will initially investigate the use the 80 Hz date from the ESA-GPOD service to investigate fine scale regional marine gravity signals. We expect that by more dense along track sampling, the along track SSH variations can be well represented and the along track oceanic surface slopes can be refined when downsampled.

The Thermal Ion Imager (TII) is one of the two instruments which compose the Electric Field Instrument on-board each of the three Swarm spacecrafts.  The TII instruments are devoted to measure the velocity and temperature of the bulk O+ distribution in the ionosphere, and to infer the ionospheric Electric field.

Despite the overall good health of the instruments and their associated equipment, in-orbit operations showed an unforeseen behaviour in the three TIIs. This is related to a non-permanent degradation of raw images that take place on continuous operations. After careful analysis of the data and several in-orbit tests, it was concluded that the observed image degradation is most likely due to water contamination in the sensor head. Several tests have been run in-orbit and a summary will be presented in the poster.

In order to tackle the unforeseen in-orbit behaviour, and for maximizing the quality of scientific data, an operational scenario was implemented where the instrument is switch-on for a few orbits per day. Discussions took place inside the Science Community, in order to achieve a sustainable operation plan for the TII, taking into account the most interesting configurations for science (e.g. particular latitude and local times, operations in conjunction with other spacecraft or ground based facilities). In this poster we will also show the new operational concept that ESA and the science experts developed in order to maximize the amount of good measurements with respect to the prevailing science needs.

The Swarm Langmuir Probes (LP) are one of the two instruments which compose the Electric Field Instrument (EFI) on board Swarm spacecraft. They are devoted to the measurement of the electron density and temperature in the ionosphere and the measurement of the spacecraft potential which is auxiliary to the data processing of the other EFI instrument, the Thermal Ion Imager.

After more than two years in operations, the Swarm LPs equipment provides high quality observations especially for electron density, which turns to be the most reliable and stable Swarm plasma parameter product. Swarm electron density data have been used successfully in many scientific studies from polar to equatorial regions.

We support even further improvements of Langmuir Probe operations, in particular: 1) the correct interpretation of the electron temperature measurements, still showing unexplained spikes widely observed throughout the whole dataset; 2) the calibration and validation of LP data by comparisons with models and independent datasets (e.g. Incoherent Scatter Radars, plasma parameters inferred from the measurement of the spacecraft’s faceplate currents).

This paper will give an overview of the LP data validation activities and results during the first 2,5 years of mission operations, and suggests future validation/calibration plans.

Established methods of seismic tomography, topography, gravity and electromagnetic data analysis and geodynamic modelling constrain distributions of seismic velocity, density, electrical conductivity, and viscosity at depth, all depending on temperature and composition of the rocks within the Earth. However, modelling and interpretation of multiple data sets provide a multifaceted image of the true thermochemical structure of the Earth that needs to be appropriately and consistently integrated. A simple combination of gravity, electromagnetic, geodynamics, petrological and seismic models alone is insufficient due to the non-uniqueness and different sensitivities of these models, and the internal consistency relationships that must connect all the intermediate parameters describing the Earth involved. In fact, global Earth models based on different observables often lead to rather different, even contradictory images of the Earth. A breakthrough in global and consistent (holistic) imaging of the fine-scale thermochemical hydrous and rheological structure of the Earth’s lithosphere and underlying mantle is needed.Thermodynamic and petrological links between seismic velocities, density, electrical conductivity, viscosity, melt, water, temperature, pressure and composition within the Earth can now be modelled accurately using new methods of computational petrology and data from laboratory experiments. The growth of very large terrestrial and satellite (e.g., Swarm, GOCE) geophysical data sets over the last few years, together with the advancement of petrological and geophysical modelling techniques, now present an opportunity for global, thermochemical and deformation 3D imaging of the lithosphere and underlying upper mantle with unprecedented resolution. However, an integrated modelling of the different data types within a self-consistent framework that exploits the different sensitivity of the constraining data sets is required to overcome the limitations and restrictions of present-day global models.

Here we present, as work in progress, a global thermochemical inversion for the structure and anisotropy of the lithosphere and underlying mantle with high lateral resolution (≈few hundreds of km) exploiting the resolving power of seismic waveforms from a very large set of source-station pairs (using all broadband data available from international data centres) together with gravity satellite observables (gravity and geoid anomalies, new gravity gradient measurements from ESA’s GOCE mission) and surface elevation within a self-consistent thermodynamic framework where seismic velocities and density are dependent on temperature, pressure and composition. 

The project European Gravity Service for Improved Emergency Management (EGSIEM) of the Horizon 2020 Framework Programme for Research and Innovation of the European Commission has started in January 2015. EGSIEM shall demonstrate that observations of the redistribution of water and ice mass derived from the current GRACE mission, the future GRACE-FO mission, and additional data provide critical and complementary information to more traditional Earth Observation products and open the door for innovative approaches to flood and drought monitoring and forecasting. We give an overview of the project and present first results from the three key objectives that EGSIEM shall address: 1) to establish a scientific combination service to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community, 2) to establish a near real-time and regional service to reduce the latency and increase the temporal resolution of the mass redistribution products, and 3) to establish a hydrological and early warning service to develop gravity-based indicators for extreme hydrological events and to demonstrate their value for flood and drought forecasting and monitoring services. All of these services shall be tailored to the various needs of the respective communities. Significant efforts shall also be devoted to transform the service products into user-friendly and easy-to-interpret data sets and the development of visualization tools.

We present the results of a study on the computation of a regional quasi-geoid model using least-squares techniques. Alternatively to the traditional compute-remove-restore procedure, we consider the GRACE/GOCE satellite gravity data as one of the noisy datasets. The regional gravity field is parameterized using spherical radial base functions (SRBFs). The SRBF coefficients are estimated using weighted least-squares techniques in combination with variance component estimation to ensure a proper data weighting. We attempt to answer the following research questions: i) how to deal with the ill-conditioning of the full noise variance-covariance matrix of the satellite gravity?; ii) is it sufficient to consider a single layer of SRBFs or does a broadband gravity signal comprising wavelength from 20,000 km to 2 km require multiple layers of SRBFs?; iii) what is a suitable functional model for the satellite gravity data; iv) how does the target area relate to the data area and the parameterization area when using the satellite gravity data?; v) should the satellite gravity data be generated at satellite altitude or at the Earth’s surface?; vi) what is the most suitable gravity field functional for the satellite gravity data? We will demonstrate that some of these questions cannot be answered yet if one aims at a one-centimetre quasi-geoid.

The Swarm Langmuir Probes (LPs) as part of the Canadian Electric Field Instrument (CEFI) with two sensors (low and high gain) on the ram side of each spacecraft provide 2 Hz electron density (Ne), electron temperature (Te), and plasma potential (fp) data along the orbital traces. The fp data are used to the benefit of an optimal working regime of the CEFI thermal ion imager (TII). The LPs use a novel ripple technique yielding derivatives of the current-voltage characteristics at three points in a rapid cycle. The traditional sweep technique is run periodically as well for verification purposes. The measurements were statistically compared with empirical numerical models like the ISO standard International Reference Ionosphere (IRI). Additionally, independent measurements from ground-based facilities like the few incoherent scatter radars worldwide are used to validate the observations during nearby overflights over the radar stations. It is shown that the Swarm LPs in the multipoint constellation allow valuable scientific insights in the physical processes of the upper ionosphere.

Investigating features of the continental crust and the upper mantle is an important goal in geophysical studies. In many cases, the Earth's crust is divided into two or three horizontal homogeneous layers but it is aimed to have a more detailed and meticulous view about crustal structure and its complexities, especially depth of the Moho discontinuity and its lateral variations. The Moho discontinuity is the surface separating the Earth's crust from the mantle. Moho depth is an important parameter in identification of crustal structure and it is also related to geological and tectonic evolution of each region. In this research, the complete gravitational gradient tensor (GGT) has been used in Euler Deconvolution algorithm for estimating the Moho depth in the structural zones of Iran. The Euler Deconvolution algorithm, which is based on using field derivatives in Euler's homogeneous equation, is an automatic method to estimate depth, shape and position of magnetic and gravity sources. This algorithm is not dependent on an initial depth and density limitations (Reid et al., 1990; Mushayandebvu et al., 2001). According to Keating (1998) and Silva & Barbosa (2003), it is particularly good to determine depth of vertical and horizontal contacts so it can be used in estimating the mantle-crust boundary (Moho depth). This algorithm includes the following three equations in which the components of GGT are used (Zhang et al. 2000).

(x‒x₀)T_xx+(y‒y₀)T_xy+(z‒z₀)T_xz=N(B_x‒T_x)          Eq. 1

(x‒x₀)T_yx+(y‒y₀)T_yy+(z‒z₀)T_yz=N(B_y‒T_y)          Eq. 2

(x‒x₀)T_zx+(y‒y₀)T_zy+(z‒z₀)T_zz=N(B_z‒T_z)          Eq. 3

In above equations T_x, T_y and T_z are the first-order derivatives of the field at the observation point (x, y, z); T_xx, T_yy, T_zz, T_xy, T_yx, T_xz, T_zx, T_yz and T_zy are the components of the gravitational gradient tensor (second-order derivatives of the field) at the observation point (x, y, z); x₀, y₀ and z₀ are the unknown coordinates of the source; B_x, B_y and B_z are the regional values of the field along the x-, y-, and z-directions; and N is the structural index (SI). SI is the rate at which the field intensity falls off with distance from the source and it depends on the type of source body which you are looking for and the type of the potential field data (magnetic or gravity); for gravity data, this factor can range from 0 to 2. To estimate Moho depth using the Euler Deconvolution algorithm it is assumed that crust-mantle boundary is a horizontal sheet or it has sill-type anomaly, which can be expressed in an infinite 2D space; the best structural index to estimate this anomaly is 0.5 (Mushayandebvu et al., 2001). An important parameter in this algorithm is window size which influences the depth of anomaly (z₀) in each solution. The window size should be small enough in order to prevent effects from multiple sources; it also should be large enough to include substantial variations of the field (Barbosa et al., 1999). The unknown parameters (x₀, y₀, z₀, B_x, B_y, B_z) are solved by least squares estimation in each window. The GGT components can be expressed in terms of spherical harmonic expansion coefficients. In this research, the first-order and second-order derivatives of the disturbing potential (T) in the geocentric Earth-fixed reference frame have been calculated using the formulas presented by Petrovskaya & Vershkov (2010) and the EGM2008 geopotential model to degree and order 360. In Figure (1), the Moho depth in structural zones of Iran, estimated by applying the GGT components in Euler Decovolution algorithm, is shown. The results indicate that the Moho depth is about 49 km beneath the main Zagros thrust, 45-48 km in the Sanandaj-Sirjan zone, 40-42 km in the Kopeh Dagh zone, less than 43 km in the Lut block, about 40 km beneath the Alborz mountains, and 30-36 km in the Makran zone.

The Dedicated Ionospheric Field Inversion (DIFI) algorithm, developed as part of the Swarm Satellite Constellation Application and Research Facility (SCARF), calculates data-based, spherical harmonic models of the quiet-time ionospheric magnetic field at mid- and low-latitudes. This field is generated by the Sq and equatorial electrojet currents flowing in the E-region of the ionosphere, near 110 km altitude, and by their induced counterparts in the Earth’s mantle. It reaches up to 150 nT at ground under the magnetic dip-equator and varies as a result of the Earth’s rotation, seasons, atmospheric tides and solar activity. A first DIFI model was calculated in 2015, based on one year and a half of Swarm magnetic measurements and additional measurements from ground-based magnetic observatories. Since this first model, the DIFI algorithm has been improved to include more sophisticated data preprocessing and model regularizations. In this presentation, we will report on a new DIFI model that will be produced in April 2016, based upon two years of Swarm data. This new model will include data at the end of 2015, when the local time separation of the Swarm A and B satellites will reach almost 3 hours, allowing a much better characterization of the ionospheric field seasonal variations. DIFI models are used to investigate source electrical currents in the ionosphere, to correct data prior to modeling magnetic fields generated by other sources, and to improve magnetic field predictions in the near-Earth environment for practical purposes such as navigation.

Gravity Recovery And Climate Experiment (GRACE) mission measures a unique variable in the Earth's water cycle - total water storage (TWS). Over the past 13 years the project centers and the science community has been trying to push the limits of the science applications of the mission. As one more step in this process, we look at computing various high resolution GRACE mass grid solutions for different temporal sampling of the earth as compared to the standard products made available by the project. These solutions are intended to be used for applications in Hydrology, Oceanography, Cryosphere etc without any need for post-processing. This paper evaluates these solutions with emphasis on the spatial and temporal characteristics of the signal content. 

Abstract

The GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) dedicated gravity satellite missions have substantially contributed to the improvement of modelling the Earth gravity field and its dynamics. They also contribute to many geodynamics and geophysics related studies as well as they revolutionized the understanding of the climate system. The GRACE-based monthly Global Geopotential Models (GGMs) have been available for more than 13.5 years. Recently, GGMs containing spherical harmonic coefficients as a function of time have been developed using GRACE and GOCE data..

Absolute gravity measurements, on a gravity test network at the Borowa Gora Geodetic-Geophysical Observatory, have been conducted on a monthly basis since September 2008 using absolute gravimeter A10-020. In this contribution temporal gravity variations obtained from RL05 GRACE-based GGMs as well as from GOCE/GRACE-based GGMs were compared with the corresponding ones obtained from the abovementioned time-series of absolute gravity measurements. The results of the comparison have been analyzed. The possibility of using monthly based time-series of absolute gravity data for calibration/validation of temporal mass variations derived from satellite observations was discussed.

Keywords. GRACE, GOCE, GGMs, Absolute gravity

The geomagnetic field is mainly composed of the core field, the crust field and fields from the current systems which are flowing in the external and internal space of the Earth. The core field and the crust field contribute most of the geomagnetic field and vary very slowly, and the other fields provide very few contributions but vary very quickly. In generally, the Earth’s magnetic field is measured by a magnetic field vector instrument and/or a scalar instrument by taking some of surveys, such as ground magnetic survey, the oceanic survey, aerial survey and satellite survey. Either of these surveys, the data quality is certainly affected by the observation environment and the performance of the instruments. Therefore, it must be required to monitor the data quality during observing and correct the disturbances before publishing data. The purpose of this work is to study the spacial-temporal distribution of the difference between the satellite measurement of the geomagnetic field and the geomagnetic field model, and to find out the reliable value of the difference, which could be used to evaluate the quality of the measurement. Data of the vector geomagnetic field are used, which is from the GFZ’s CHAMP satellite during 2000 and 2010, and the ESA’s SWARM mission since 2014. Meanwhile, the core field and crust field are calculated by the CHAOS-4 model. The difference between the model result and the satellite data are computed. Then the distribution of the difference value is analyzed not only along with the latitude, but also in view of the conditions of the geomagnetic activity (Dst index) and the solar activity (F107 index). The result of this study could provide some valuable suggestions for the preliminary evaluating of the geomagnetic field measurement of the Chinese TC-03 in the future.

Integral transformations of the disturbing potential derived from satellite altimetry onto satellite-to-satellite tracking data are formulated, investigated and applied in this contribution. First, corresponding differential operators, that relate the disturbing potential to the disturbing potential differences and the line-of-sight gravity disturbances, are applied to the spherical Abel-Poisson integral. This yields two integral transformations for which respective kernel functions are given in both spectral and spatial forms. Second, truncation error formulas for both integral transformations are provided in the spectral form. Also expressions for the corresponding truncation error coefficients are provided. Third, practical estimators for evaluation of the disturbing potential differences and the line-of-sight gravity disturbances are formulated, and their correctness and expected accuracy are investigated. In particular, we investigate the error propagation through truncated integration, and the omission and commission errors, which are related to the evaluation of the distant zones, for the GRACE satellite mission.

It has been known that magnetospheric electric field penetrates to the ionosphere has an effective role in the formation of the Equatorial Ionospheric Anomaly (EIA). Due to the lack of observational space points and the narrow local time of satellite at low altitudes it has been difficult to study the instantaneous effect of the magnetospheric electric field at the ionosphere. Using electric field data from Van Allen Probes and THEMIS satellites, while the Field Aligned Current (FAC) and electron density data from SWARM satellite. We present a case study of bipolar electric field associated to sudden commencement observed in the deep magnetospheric interior to study the role of the bipolar magnetospheric electric field in the formation of ionospheric single crest and the FAC at low and equatorial latitude regions. A case study of bipolar magnetospheric electric field observation on March 25, 2014 revealed that the polarity of magnetospheric electric field showed instantaneous effect on suppressing or enhancing the electron density of the EIA observed by SWARM satellite. Electron temperature showed fluctuations between 20 ^o and 25^o Celsius within 2 minutes from electric field onset. FAC showed a sudden response to magnetospheric electric field and east west ground based magnetometer data at the vertical projection of SWARM-A satellite also showed instantaneous variation. The observational case study is important in understanding the role of electric field in the evolution of the ionospheric single crest and the FAC at low latitude region.

The gravity fields produced by the Gravity Recovery And Climate Experiment (GRACE) satellite mission are contaminated by noise. Therefore, filtering is essential to extract meaningful information. Filtering suppresses noise, but also changes the signal which increases the uncertainty in GRACE results. Several efforts have been made to minimize the effects of filtering on the signal, such as the additive approach, the multiplicative approach, the scaling approach and many more. However, all these approaches use hydro-geophysical models to compute mathematical quantities such as bias, leakage or scale factors, which are used to improve the filtered GRACE products. Since GRACE should ideally improve the hydrological models, we do not want to use models to improve GRACE. A common assumption in previous approaches was that filtering affects only the amplitude of the signal, but we show that the phase is also affected. We propose a data driven methodology to minimize effects of filtering. We provide a mathematical relation between the true signal and the filtered signal that does not depend on models. First we validate our methodology in a closed-loop environment, and then we show that our method is performing better than other popular methodologies. We apply this strategy to GRACE products and validate the results.

In order to take advantage of the unique constellation aspect of ESA's Swarm constellation mission, considerably advanced data analysis tools have been developed. The Swarm ESL/SCARF (Satellite Constellation Application and Research Facility), a consortium of several research institutions, derives Level-2 products by combination of data from the three satellites, and of the various instruments.

A number of Level-2 data products are defined and produced by this consortium, including various models of the core and lithospheric field, as well as of the ionospheric and magnetospheric field. In addition, derived parameters like mantle conductivity, thermospheric mass density and winds, field-aligned currents, an ionospheric plasma bubble index, the ionospheric total electron content and the dayside equatorial zonal electrical field are determined.

The present poster describes the various processing chains of SCARF, the Level-2 output data products defined and produced by SCARF, and the timeline of Level-2 product generation.

As part of the ESA living planet programme the Swarm mission started in November 2013. During the following four years this multi-satellite project will provide information about the Earth’s magnetic field to finally produce a model of the magnetic field with a high resolution never reached before. Therefore, the three satellites are equipped with Absolute Scalar Magnetometers and Vector-Field Magnetometers. Moreover, a special orbit configuration was chosen with two parallel-flying satellites in a lower orbit compared to the third one. During the mission lifetime the angle between the orbital planes of the lower satellites and the upper satellite will shift from 0° to 90°.

To reach the goal of a high-resolution model of the Earth’s magnetic field, it is important to know the exact position and attitude of all satellites and their instruments. By integrating star trackers and GPS equipment on the satellites, this information is available for each satellite. Apart from this main objective, the mission strategy additionally foresees a major contribution to the studies of thermosphere and gravity field. Therefore, each satellite is equipped with an accelerometer placed in the center of mass of the satellite. Thus, it is possible to measure non-gravitational forces, like solar pressure or atmospheric drag, on the satellites.

Our investigations concentrate on the assessment of the quality of the observations made by the three instruments mentioned above. We describe the anomalies we found during our data analyses and illustrate their characteristics (predominantly) in the spatial domain. Additionally, we give insights in our interpretations of those anomalies.

The auroral electrojets are large horizontal currents that flow within the ionosphere in ovals around the polar regions. They are an important aspect of space weather and their position and intensity vary with solar wind conditions and geomagnetic activity. The electrojet positions are also governed by the Earth's main magnetic field. During more active periods, the auroral electrojets typically move equatorward and become more intense. This causes a range of effects on Earth and in space, including geomagnetically induced currents in power transmission networks, disturbance to radio communications and increased drag on satellites due to expansion of the atmosphere. They are also indicative of where the aurora are visible. 

Monitoring of the auroral electrojets in the pre-satellite era was limited to the network of ground-based magnetic observatories, from which the traditional AE activity indices are produced. These suffer in particular from the stations' poor distribution in position and so this motivates the use of satellite-based measurements. With polar low-Earth orbit satellites carrying magnetometers, all latitudes can be sampled with excellent resolution. 

This poster presents an investigation using Swarm's magnetometer data to detect the electrojets as the spacecraft move above them. We compare and contrast two approaches, one which uses vector data and the other which uses scalar data (Hamilton and Macmillan 2013, Vennerstrom and Moretto, 2013). Using ideas from both approaches we determine the oval positions and intensities from Swarm and earlier satellites. The variation in latitude and intensity with solar wind conditions, geomagnetic activity and secular variation of the main field is investigated. We aim to elucidate the relative importance of these factors. 

Hamilton, B. and Macmillan, S., 2013. Investigation of decadal scale changes in the auroral oval positions using Magsat and CHAMP data. Poster at IAGA 12th Scientific Assembly, 2013. http://nora.nerc.ac.uk/503037/  
Vennerstrom, S. and Moretto, T., 2013. Monitoring auroral electrojets with satellite data. Space Weather, VOL. 11, 509–519, doi:10.1002/swe.20090

GPS-derived kinematic precise Swarm orbits are significantly affected by increased position noise over the geomagnetic poles and spurious signatures along the geomagnetic equator. The latter deficiencies were identified for the first time for the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission and are related to the distortion of the GPS carrier signal when propagating through portions of the Earth's ionosphere with a large free electron content. Via the GPS-derived kinematic Swarm positions, especially the spurious signatures along the geomagnetic equator map directly into the derived gravity fields. This was already the case for GOCE and obviously is also true for Swarm.

The systematic degradations of the orbits along the geomagnetic equator indicate on the one hand that the GPS observation model and/or the data pre-processing need to be improved, and that, on the other hand, there might exist receiver-specific tracking problems.

To analyze the root cause of the problem, we first characterize the stochastic and systematic behavior of the ionosphere by analyzing GPS data collected by the GPS receivers of various LEO satellites covering a broad altitude range (CHAMP, GRACE, GOCE, Swarm A-C, and Sentinel) and for time periods covering significant parts of an entire solar cycle, which probes substantially different ionosphere conditions. Furthermore, the attempt will be made to correlate the GPS tracking performance with the local electron density measured by the Swarm Langmuir probes.

The obtained information provides the basis for improvements of the data pre-processing to cope with the ionosphere-induced problems of LEO precise orbit determination. The performance of cycle slip detection can, e.g., be degraded by large changes of ionospheric refraction from one measurement epoch to the next. Geographically resolved information on the stochastic properties of the ionosphere above the LEO satellites will provide more realistic threshold values for cycle slip detection and screening algorithms.

Mitigating ionosphere-induced artifacts in orbit and gravity field products may be achieved by omitting GPS data showing large ionospheric variations. Using the detailed characterization of the ionosphere, more advanced data screening or data weighting schemes will be assessed in the GPS data processing for the Swarm precise orbit determination.

In an attempt to identify potential deficiencies in the GPS observation model, the impact of higher order ionosphere corrections on the so-called "ionosphere-free" observable will be studied. The knowledge of the total electron content (TEC) along the line of sight is essential for that purpose. These TEC values are obtained either from global ionospheric maps together with realistic location-dependent scale heights from the International Reference Ionosphere model, or directly from the GPS phase measurements. Comparisons with the Swarm level-2 TEC products will be conducted, as well.

In this study, the GOCE (Gravity field and steady state Ocean Circulation Explorer) gradiometry data were used to study geologic structures and mass variations within the lithosphere in areas of known subduction zones. The advantage of gravity gradiometry over other gravity methods is that gradients are extremely sensitive to localized density contrasts within regional geological settings, which makes it ideally suited for detecting subduction zones. Second order gravity gradients of disturbing potential were extracted from global geopotential model, the fifth release GOCE model ‘EGM_TIM_RL05’. In order to remove the signal which mainly corresponds to the gravity signal of the lower mantle, long wavelength part of the gravity signal was removed up to degree and order 60. Because the areas with notable topography differences coincide with subduction zones, topography correction was also performed. Few pattern recognition methods were tested on all 6 gravity gradient tensor components represented as global scale maps with resolution of 100km (corresponds to the resolution of the GOCE satellite data). By adjusting pattern recognition methods’ features and optimizing various input patterns, the best method was applied. That is a combination of methods based on SURF (Speeded Up Robust Features) and MSER (Maximally Stable Extremal Regions) algorithms provided in MATLAB’s Computer Vision System Toolbox. Based on 6 gravity gradient components, the global gradient anomaly maps were produced and used as starting point for analysis based on image processing. On obtained maps, locations of known subduction zones were represented with characteristic elongated patterns and cross-sections. Cross sections of well-known subduction zones were used as input patterns for pattern recognition method on global maps. The search for discrete point correspondences between these images was divided into three main steps: Interest point detection, interest point description and matching between images. Resulting routine compares vertical gravity gradient anomaly signal in the areas with known subduction zones with all locations on the Earth (covered by GOCE gravity gradients). Searching, comparing and detecting the compatible signal lead to correct detection of all known subduction zones but also gave indications for locations of unknown subduction. Apart from subduction zones, certain geological features were detected and studied. The method proved its advantages and should be easily adjusted and conducted on other datasets with similar representations.

The European Space Agency (ESA) Swarm mission was launched on 22 November 2013 and consists of three identical satellites, flying in carefully selected orbits. Precise Science Orbits (PSOs) are computed for this satellite constellation using GPS data from the onboard 8-channel dual-frequency GPS receivers. The delivered PSOs consist of a reduced-dynamic orbit for the geolocation of the onboard scientific instrument observations with highest accuracy, and a kinematic orbit for gravity field determination purposes.

In addition to their use for precise orbit determination, the GPS receivers can also be used to calibrate the accelerometer instruments, which are also part of the scientific satellite payload in order to derive information about the atmospheric density and winds. Unfortunately, the Swarm accelerometer measurements suffer from a variety of unexpected disturbances, which severely affects their usefulness. Therefore, an alternative approach has been developed to derive atmospheric density, based on the high-quality Swarm GPS observations. In this approach the non-gravitational accelerations are estimated directly from the GPS data, albeit at a much lower temporal resolution than the accelerometer. These estimated accelerations can be used to generate low-resolution Swarm densities, as well as to validate the corrections that have been developed to restore the accelerometer observations.

In this presentation we describe the adopted orbit determination strategy for both PSO orbits, together with an assessment of their accuracy. Independent satellite laser validation using onboard laser retro-reflectors shows that the accuracy of the reduced-dynamic Swarm orbits is better than 2 cm, while the kinematic orbits have a slightly reduced accuracy of about 4 cm. In addition, we present our alternative approach to estimate non-gravitational accelerations from the GPS observations and give an assessment of the obtainable resolution and accuracy.

With the release of new high-resolution data from the Jason-1 and CryoSat-2 satellites, there has been renewed interest in developing new satellite-derived gravity data. By combining the new data with the existing data from, the ERS-1 and Geosat satellites, we have been able to improve the coverage and resolution of our gravity data sets in continental margins. We have seen particular improvement in our gravity data sets in coastal regions. However, with the addition of new data from conventional pulse-limited altimeters, we are limited to improving track coverage near the coast, but not extending it closer to the coast as land-based reflections and diffractions  will affect the tracking of the ocean-based waveform, setting a limit as to how close to the coast we can accurately determine the sea surface height.

In this study we show how we can extend the track coverage in coastal areas by incorporating the synthetic aperture radar (SAR) mode from CryoSat-2 into our offshore global gravity solution. The SAR mode from CryoSat-2 has an along-track and cross-track footprint of ~0.29 km and ~5 km respectively, whereas the conventional low-resolution mode (LRM) from CryoSat-2 has a ~5 km diameter footprint. The decreased footprint size using the SAR mode allows the tracking of the ocean-based waveform closer to the coast.

First, we directly compared two co-linear satellite tracks off the coast of Central Sulawesi, where the satellite was in LRM mode one year and in SAR mode another year. Waveforms that have been contaminated by land-based signals were identified in both modes and can have very high amplitudes if they originate from highly reflective surfaces such as beaches. As the satellite approached the coast, we were able to observe the contaminated waveforms in the LRM mode before they were visible in the SAR mode; these land-based reflections adversely affect the re-tracking of the waveform, allowing the SAR waveform to be re-tracked closer to the coast.

We then investigated 315 SAR and 330 LRM tracks off the coast of India, identified the waveforms that have been contaminated by land-based reflections, and determined the minimum distance from the coast to which we can accurately re-track the ocean-based waveform. We found that, on average, we could reliably re-track LRM waveforms up to a distance of 3.5 km from the coast, while SAR waveforms could be re-tracked up to a distance of 2.4 km from the coast. Moreover, when the satellite trajectory is perpendicular to the coastline, the improved along-track resolution of the SAR mode allowed waveforms to be re-tracked up to a distance of 0.5 km from the coast. By successfully incorporating SAR mode data into our satellite-derived gravity, we have shown that the SAR mode from CryoSat-2 improves coverage in coastal regions and this should lead to better resolution in satellite-derived gravity near the coast where CryoSat-2 is in SAR mode.

The time-frequency analysis (TFA) tool is a suite of algorithms based on wavelet transforms and neural networks, tailored to the analysis of L1b data from the Swarm mission. The aim of the TFA tool has been to combine the advantages of multi-spacecraft and ground-based monitoring of the geospace environment in order to analyze and study magnetospheric ultra low frequency (ULF) waves. Additionally, the tool has been offered a useful platform to monitor the wave evolution from the outer boundaries of Earth’s magnetosphere through the topside ionosphere down to the surface. Here, we present the revised TFA  (R-TFA) tool introducing a new user-friendly interface and presenting a number of applications and capabilities that have not been previously included in the earlier versions of the tool.

Knowledge of the static gravity field is of importance for various scientific disciplines, such as geodesy, geophysics and oceanography. While for geophysics the gravity field provides insight into the Earth’s interior, the geoid serves as an important reference surface for oceanographic applications. Moreover this reference surface is a key parameter on the way to a globally unified height system.

In order to exploit the full potential of GOCE’s measurements and to achieve the best gravity field solution, GOCE information has to be combined with complementary gravity field information. First Gravity Recovery and Climate Experiment (GRACE) information, highly accurate in the very long wavelength part, is included. Secondly information from terrestrial measurements and altimetry, measurement techniques which provide short wavelength gravity information beyond the resolution of GOCE, is included to cover the full gravity field spectrum. Therefore, these three components complement each other.

This paper focus on the question how GOCE and the complementary data types can be combined in a global gravity field model in the way that all data types keep their specific strengths and  are not degraded by the combination with other information in certain wavelengths. A global gravity field model up to degree and order 720 based on full normal equation systems (more than 500,000 parameters) will be presented. Realistic stochastic modelling and a tailored weighting scheme among all available data results in different regional relative weighting of satellite and terrestrial data in the combined solution, mainly depending on the quality of the available terrestrial gravity information. From this procedure, as complementary product realistic error estimates are available in terms of a full-covariance matrix, which can be mapped in a spatial error grid reflecting regionally specific uncertainty estimates. The analysis of the model will demonstrate the contribution of GOCE in a combined global gravity field solution. The application of the model in oceanographic analyses exhibits the improved performance due to the GOCE data.

Aiming for an as accurate as possible estimation of mass trends in Antarctica or other regions, based on global GRACE gravity field solutions, calls for best possible post processing strategies. Decorrelation filters employing static covariance information have already been developed in the past (e.g. DDK filter series by Jürgen Kusche 2007 & 2009), but covariance information for a decade long recent time series was not publicly available since the publication of the ITSG temporal gravity field model in October 2014.

With this work we aim to use this time series with its evolving correlation structures due to changing mission configuration (e.g. orbital height) and instrument characteristics over time.

Proper reduction of correlated errors is a crucial step towards trend estimation. For this purpose we analyzed the existing series of DDK filters based on static or simplified assumptions on the correlation structure of spherical harmonic coefficients and target signals. To analyze the potential gain using month to month full covariance information we have tested the impact of certain simplifications (e.g. the ones applied for the DDK filters) with respect to the full covariance information in a closed loop simulator. Variables investigated within this experiment are for the error covariance matrices full, order-block and diagonal structures and for the signal variance matrices “real”, “mean” and “l-rule” (degree dependent) signal content.

Based on the outcome of the simulated results we computed new decorrelation filters using full error covariance information and investigated the impact on basin scale mass change estimates in the Antarctic region. These results are compared to the ones obtained from DDK, Swenson & Wahr type and other filters as well as independently derived results from e.g. radar altimetry.

Scale factors, thermal behavior, EDACs

The Swarm satellites were launched on 22 November 2013 and carry accelerometers as part of their scientific payload. These instruments measure the non-gravitational acceleration due to forces like drag or radiation pressure acting on the spacecraft, from which thermospheric neutral densities and potentially winds can be derived. Unfortunately, the acceleration measurements suffer from a variety of disturbances, the most prominent being slow temperature-induced bias variations and sudden bias changes.

A sequence of thermal tests explored the capability of the available heaters to reduce the temperature variations at the orbital period, ultimately aiming at improved accelerometer measurements. The main finding of these tests is that due to insufficient heater power and lack of thermal insulation it will not possible to eliminate the temperature variations. Thus, the slow temperature-induced bias variations have to be handled in the on-ground processing of accelerometer data.

Another particular challenge is the determination of the accelerometer scale factors in presence of the slow temperature-induced bias variations. A newly developed method is based on dedicated sequences of relatively short attitude thruster activations that create linear accelerations acting on the satellites. Since the thrust force and satellite mass are known with a small uncertainty, the magnitude of the linear accelerations can be deduced and compared to the measured accelerations.

In this presentation, we illustrate all known disturbances and explain the tests that were performed in order to understand better and mitigate the effect of the disturbances on the measurements.

Groundwater plays a key role in the terrestrial hydrological cycle and the water balance on the continents. It accounts for more than 30% (i.e., 8,000,000 km3 to 10,000,000 km3) of global fresh-water resources, and is also the major resource of water supply for 40% of the world's population and 50% of the world's food production. However, groundwater storage and its variations are still poorly known at global scale due to the limited extent of current monitoring networks. Most of the studies on geohydrology in the Amazon basin were carried out at local scale except a recent study that pointed out evidences on regional scale groundwater flows using a geothermal method. Gravimetry from space offers the unique opportunity to monitor water resources at basin to continental scales. The Gravity Recovery And Climate Experiment (GRACE) mission, launched in 2002, detects tiny changes in the Earth's gravity field which can be related to spatio-temporal variations of TWS at monthly or sub-monthly time-scales. Variations in groundwater storage (GW) can be separated from the TWS anomalies measured by GRACE using external information on the other hydrological reservoirs such as in situ observations, model outputs, or both. Very few studies have been undertaken yet in large river basins characterized by extensive wetlands and floodplains, due to the lack of reliable and timely information about the extent, spatial distribution, as well as the amount of water stored in wetlands and floods and their temporal variations. Using multi-satellite observations for surface water storage (SW) and hydrological outputs for soil moisture (SM), variations in GW were estimated in the Negro basin, the second largest tributary of the Amazon in terms of discharge. Here, the same approach was applied in the whole Amazon basin, allowing to estimate the contribution of each hydrological reservoir to TWS, to monitor its time variations, and to map the annual changes in the aquifers over 2003-2007. These estimates were compared to hydrological model outputs from WGHM and ISBA and validated against in situ data from wells. For the whole Amazon basin, SW, SM and GW represent around 45%, 25%, and 30% of the TWS respectively.

The GOCE User Toolbox GUT is a compilation of tools for the utilisation and analysis of GOCE Level 2 products.
GUT support applications in Geodesy, Oceanography and Solid Earth Physics. The GUT Tutorial provides information
and guidance in how to use the toolbox for a variety of applications. GUT consists of a series of advanced
computer routines that carry out the required computations. It may be used on Windows PCs, UNIX/Linux Workstations,
and Mac. The toolbox is supported by The GUT Algorithm Description and User Guide and The GUT
Install Guide. A set of a-priori data and models are made available as well. Without any doubt the development
of the GOCE user toolbox have played a major role in paving the way to successful use of the GOCE data for
oceanography.

The GUT version 2.2 was released in April 2014 and beside some bug-fixes it adds the capability for the computation of Simple Bouguer Anomaly (Solid-Earth). During this fall a new GUT version 3 has been released. GUTv3 was further developed through a collaborative effort where the scientific communities participate aiming
on an implementation of remaining functionalities facilitating a wider span of research in the fields of Geodesy,
Oceanography and Solid earth studies.
Accordingly, the GUT version 3 has:


- An attractive and easy to use Graphic User Interface (GUI) for the toolbox,


- Enhance the toolbox with some further software functionalities such as to facilitate the use of gradients,
anisotropic diffusive filtering and computation of Bouguer and isostatic gravity anomalies.


- An associated GUT VCM tool for analyzing the GOCE variance covariance matrices.

The aim of this study is to investigate the magnetic perturbations caused by the polar electrojets, which are described by means of a model consisting of a series of infinite line currents placed at the height of the ionosphere along QD latitudes.

The method is applied to Swarm magnetic scalar perturbations (which means observations after removal of contributions from the core, crust and the large-scale magnetosphere) in the Polar Regions (+/- 50 degrees from the poles) for individual satellite passes.

The obtained estimates of ionospheric currents provide information on the position and strength of the polar electrojets as well as their temporal evolution. In addition, applying the method to data taken by the Swarm satellites Alpha and Beta allows investigating longitudinal differences of the electrojets. 

The improved gravity models provided by the GOCE mission have enhanced the resolution and sharpened the boundaries of those features and the associated geostrophic surface currents reveal improvements for all of the ocean’s current systems. There are still important signals to be recovered and issues related to errors in the models have been identified.

In this study, a series of newer gravity models including observations from GRACE and GOCE are compared with the DTU15MSS mean sea surface to analyse resolution capacities and to identify issues caused by errors in the models. The comparisons are carried out in regional analyses using Fourier techniques to derive the spectral characteristics as well as anisotropic patterns to identify differences and to quantify quality measures associated with the models. In addition, regional analyses are carried out using in-situ observations of the geostrophic surface currents from drifters. This is done to analyse correlations and to derive resolution capacities associated with the ocean circulation and to derive requirements to future gravity missions. 

Magnetic data collected by the Swarm trio of satellites, together with those obtained from two previous spatial missions (Oersted and CHAMP), make it possible to reconstruct with an unprecedent temporal accuracy the evolution of interannual fluid motions within the Earth's outer core. This is of particular interest since the Alfven period, a fundamental characteristic time scale of the core dynamics, is about 4 years. Furthermore, particularly intense interannual magnetic signatures have been detected over the past decade in the equatorial area. We reconstruct rapidly changing core motions at periods longer than a year, and propose that the observed magnetic patterns arise from transient quasi-geostrophic core flows. We describe axisymmetric torsional Alfven waves propagating outward, potentially triggered by non-axisymmetric motions of larger intensity. At the shortest available periods we investigate the first harmonic of these waves, and its signature in length-of-day data.

In this project we will deliver two new data products to the Swarm user community:

•The polar cap patch index which identifies whether a measurement was taken inside a polar cap patch; and

•The gradient drift instability growth time and its error which quantifies the rate at which kilometer-scale plasma density gradients are broken down into meter-scale plasma density structures.

In order to calculate these new data products, we will use existing Swarm level 1b data products. The Electric Field Instrument (EFI) on board all Swarm satellites provides as part of the level 1b plasma data products measurements of the plasma density by the Langmuir Probe. In the polar regions above about 75 degree latitude, however, these measurement provide no context, i.e., it is currently not possible for the user to routinely determine whether a particular measurement is part of a larger plasma structure or not. One example for such a larger-scale plasma structure (several hundred kilometers in extent) is the polar cap patch which is of increasing import in a space weather context. Using the accepted definition that a polar cap patch is a region within the polar cap where the plasma density is enhanced by more than a factor of two above the background density, this work will provide a polar cap patch index. The polar cap patch index will identify whether a plasma density measurement is part of a polar cap patch or not. The challenge of developing a polar cap patch detection routine will be to identify polar cap patch boundaries automatically, correctly and in a robust manner. Once a polar cap patch has been identified, its impact in a space weather context can be assessed by calculating a new parameter using level 1b data routinely provided by Swarm. The suite of level 1b plasma data products also includes measurements of the ion drift velocity from the Thermal Ion Imager. After the start and end positions of a polar cap patch have been identified in the plasma density data, the ion drift measurements can be used to define the leading and trailing edge of the polar cap patch. The leading edge is defined as that boundary of the polar cap patch where the plasma density gradient is anti-parallel to the ion drift, whereas at the trailing edge the two vectors are parallel. This differentiation between leading and trailing edge is important because plasma density gradients which are parallel to the background ion drift are susceptible to a plasma instability called the gradient drift instability (GDI) whereas gradients that are anti-parallel to the ion drift are not. The rate at which the GDI erodes the trailing edge is determined by the GDI growth time which will be the second new data product coming out of this project. Its value can be calculated from the magnitude of the plasma density gradient and the ion drift at the center of the gradient. Therefore, the challenge here is the accurate determination of the plasma density gradients and their errors in order to ensure a reliable estimate of the GDI growth time. 

The high resolution global gravity fields provided by different satellite missions could be used in Glacial Isostatic Adjustment (GIA) modelling. To use this dataset bandpass filtering of spherical harmonic coefficients in the static gravity field is suggested to separate the GIA effect from other sources. Studies using this methodology found correlations between the gravity field and the GIA gravity signal. However, the truncation of the spherical harmonic coefficients boundaries vary in those studies.

We will look at different GIA models and locations to see the effect of spectral truncation of the spherical harmonics coefficients on the static gravity field component of such models. Areas with ongoing glacial rebound, like Laurentia, Fennoscandia, Antarctica, Patagonia, and Barents Sea are inspected. For the GIA models, the complete sea level equation will be solved and resulting gravity potential fields are determined. Two different modelling approaches are used for the solid Earth movement: normal modes modelling and finite element modelling (3D rheology). This is done to inspect the difference by introducing 3D Earth rheology. The models will be constrained by geologically determined relative sea level curves, GPS-based uplift, and GRACE-based gravity change observations. Model results will be compared with observed static gravity field from satellite gravimetry to determine any correlation.

The geological sources of large satellite magnetic field anomalies correspond to crustal-scale magnetized bodies. Therefore identifying a single geological unit as the source is difficult since such anomalies mainly appear above old mountain belts or cratonic regions, which are often very heterogeneous. Additionnally,  for geographical (few exposures) or geopolitical reasons, the field identification of some of these sources sometimes remains impossible. Our study focuses on the West African magnetic field anomaly. Few source models were published, and most of them are simplistic. For instance, the effect of the remanent magnetization is often not considered. Here we constrain a numerical model of the crust beneath the anomaly using geological maps, cross-sections and a number of rock samples from this region. Starting from local scale (Kediat Ijil area) to the regional scale (Reguibat ridge). Banded Iron Formation rocks of the Reguibat ridge are the only one with magnetic characteristics strong enough to cause the observed anomaly. New susceptibility and remanent magnetization measurements on those BIFs samples are performed. We also study the effect of crustal depth pressure on the magnetization, by applying thermal demagnetization on samples under 1 GPa. These measurements, as well as the Bouguer gravity anomalies, and sediments and crustal thickness values, are used to constrain the model. Our model fits the WDMAM magnetic anomaly grid, which – in this area - was built using a combination of several data sets (ground data, aeromagnetic data, satellite data…). The preliminary predictions of SWARM data using this model seem relevant, but this is still being investigated.

The combination of a low orbital altitude and extremely sensitive accelerometers have made the GOCE satellite a unique platform for investigations into orbit and attitude perturbations due to aerodynamic forces and torques in low earth orbit. Recent studies have focused on the extraction of aerodynamic forces acting on the satellite, which have been converted into unique data on thermospheric density and cross-winds. However, the influence of several aerodynamic model parameters, including the satellite wall temperature and accommodation coefficient, remain to be investigated in detail.

To facilitate the investigation of these parameters, more information regarding the aerodynamic disturbance is required. Therefore in this paper we present our approach to deriving the aerodynamic torques from the gradiometer readings. This involves a thorough modeling of the most significant other torques. First and foremost, the control torque is calculated by combining the magnetic torquer currents and the magnetometer measurements. Then the solar and Earth albedo radiation pressure torques are modeled, using moment coefficients from a radiation pressure Monte-Carlo simulation. A simplified Earth gravity field model is used to provide the gravity gradient torque. Finally the moment due to the misalignment of the ion thruster’s line of action with respect to the center of mass is added. The remaining angular acceleration is assumed to be caused by aerodynamic effects, and is therefore compared to a model based on moment coefficients determined using a free molecular flow Monte-Carlo simulation.

The results will first of all provide insight in the required level of detail in the models of other disturbance and control torques. Second, comparing the frequency spectra of the modeled and measured aerodynamic torque, signals may be found that are not taken into account by the aerodynamic model. Finally the difference in magnitude of the same signals may indicate modeling errors in the magnitude of thermospheric density, cross-winds and the accommodation coefficients of the satellite wall.

Computation of the geoid model has been completed at the Institute of Geodesy and Geoinformatics (LU GGI) for the Eastern part of Latvia using the densified GNSS/levelling network data and DFHRS software (Digital Finite-element Height Reference Surface, developed at the Karlsruhe University of Applied Sciences, Germany). The abbreviation of the new geoid model is GGI/DFHRS quasigeoid model. On the 154 levelling points were performed the single GNSS 4 hour long measuring sessions by the staff of GGI. The EPN reference station network observation data were used for both the single GNSS station, LatPos and EUPOS-Riga reference network precise point position computation using Bernese 5.2 software. All the results were reduced to the epoch of 2015.0 by applying 7 parameter Helmert transformation. Additionally, 120 GNSS/levelling point data were included which were obtained from the Latvian Geospatial Agency (LGIA). As consequence, the average distance between the points appears about 10 km.

The new Latvian height system is named LAS14 (Latvijas augstumu sistēma 2014). Official 1^st and 2^nd order LAS14 height system’s normal heights of the epoch 2000.5 are presented by LGIA. LAS14 is the European Normal height system’s EVRS2007 realization in Latvia. LAS14 height values together with LU GGI measured ellipsoidal height data were used for GGI/DFHRS computation.

Ellipsoidal heights of GNSS/levelling points were  computed in ITRF08 system using EPN reference data, reduced to ETRS89 and   converted by Helmert transformation to ETRS89 at epoch 2015.0 in order to be included or avoided  both the GNSS measuring and national network’s local deformations.

Two versions of GGI/DFHRS models were computed by applying as initial both the international global gravity models EGG97 and EGM2008 correspondingly. The computation residual’s  standard deviation for the LU GGI/DFHRS geoid model is 6 mm with an EGG97 (99% residuals ≤ 12 mm) and 12 mm with an EGM2008 (89% residuals ≤ 12 mm) . However, it has been experienced that the GNSS observation quality strongly depend from the environmental conditions and multipath. The objectives of the project is achieved by obtaining the 1 cm precision quasigeoid model for GNSS measurements in test area of Eastern part of Latvia. Hopefully, it will be used in GNSS measurements in geodesy, land surveying and other tasks of civil engineering.

A prototype of new device for both positional and SLR observations of near-Earth objects (satellites, space debris, natural objects) has been designed at the LU  GGI in a joint research project with Institute of Physics of the University of Latvia. The device uses commercial high quality   twin 42 cm optical tube assemblies. One of them used for astrometric functions, the other - as SLR receiver. A separate collimator is used for transmitted laser pulse handling. Presently the functional tests are completed, the device is being deployed in it's dedicated location.

As result of our previous research, the design of a new fully automated digital zenith camera for vertical deflection determination is finished. Field tests of the camera now are proceeding.

Recently developed automated methods for detecting and deriving the characteristics of ultra low frequency (ULF) waves are applied to the Swarm data sets in order to retrieve new information about the near-Earth electromagnetic environment. Here, we present the first ULF wave observations by Swarm, by performing a statistical study on the occurence and properties of Pc3 waves (20–100 mHz) for a time period spanning two years. We derive distributions for various properties of the detected wave events (amplitude, peak frequency, duration, badnwidth) and examine evidence for the decay of the amplitude of the Pc3 signal with altitude, as predicted by theoretical models of wave propagation. We show that the major characteristics of the Swarm ULF power maps generally agree between observations made by the upper satellite and the lower pair of satellites, when the power spectrum of the upper satellite is shifted in local time, to account for the angular separation between their orbital planes. Moreover, a puzzling enhancement, not predicted by current ULF wave theories, of  compressional Pc3 wave energy was revealed by Swarm in the region of the South Atlantic Anomaly.

The ESA Swarm satellites, launched in November 2013, carry on-board instuments devoted to measure extremely accurate data necessary to improve our understanding of Earth’s magnetic field. The Swarm instrument package is made by two magnetometers (one vector and one scalar), one Electric field Instrument (EFI), one Accelerometer and one GPS reciever. This presentation aims at providing an extensive overview of the magnetic instrument status, magnetic data availability and quality.

Thermal Plasma Measurement Unit (TPMU) scientific instrument was developed for PROBA II microsatellite and launched in November 2009. The device is working with limitations of scientific measurements caused very probably by installed on-board software. This brings lower data volume as it was planned. Affected are ion measurement and partially electron temperature measurement.

The measurement of the floating potential are not affected. This behaviour of the instrument is stable and lasting since begin of the mission. Measured floating potential data are completed with orbital parameters. We implement the time-series decomposition to recognize seasonal and non-periodic components. The analysis is performed for all seasons of the period from May 2010 to December 2015 for the Equatorial region, North and South hemisphere. The data are divided to three groups by geographical latitudes to the Nothern hemisphere (lat>15‘), the Southern hemisphere  (lat<-5‘) and Equatorial zone (lat 15‘– -15‘). The Kp, Dst and the satellite insolation parameters were included in the model.

The annual seasonal changes in the floating potential are observed in this analysis. Changes in the beginning, the end and duration of seasons over a period of years reflect also changes of Kp index. Changes over the solar cycle are also visible.

The important TPMU goal is the validation and testing of the novel design of the instrument which is necessary for possible applications of TPMU design on future scientific missions.

The similarities in time profiles of floating potential, electron temperatures and Kp index was identified. This proves that the measurement of electron temperatures react physically and have only systematically biased.

In this research, a modified form of Vening Meinesz-Moritz (VMM) theory of isostasy for the second-order radial derivative of geopotential measured from steady-state ocean circulation explorer (GOCE) is developed for local Moho depth recovery. An integral equation is organised for inverting the GOCE data to compute a Moho model in combination with SRTM30 and applied over the Indo-Pak plate. The kernel of this integral is well-behaving and approaches zero at 15° geocentric angle meaning that this integral is suitable for local Moho recovery. A Moho model from no-topographic gravity disturbance from the harmonic coefficients of EGM08 to degree and order 180° is also computed for the purpose of comparison. Numerical results show that GOCE data are more sensitive to the local crustal heterogeneties and Moho undulations over the plate are in close correlation with CRUST1.0 model. In addition, our GOCE-based Moho model, with a root mean squares error of 1.5 km, is closer to the seismic model of CRUST1.0 than that recovered from EGM08. The local and anomalous features of this model are not visible in the one generated from EGM08 but they are consistent with the Moho model of CRUST1.0.

Perhaps one of the biggest difficulties in modelling the Earth’s lithospheric magnetic field is the separation of contributions from sources of internal and external origin. In particular, the determination of smaller-scale lithospheric magnetic field features is problematic because the lithospheric signal is contaminated by much larger and highly time-dependent contributions from sources in the ionosphere and magnetosphere. Simultaneous, high-quality measurements from different locations as well as gradient estimates provided by the three Swarm satellites open new possibilities in lithospheric field modeling. Field gradients can be approximated by employing along-track and across-track field differences which act as high-pass filters of the data and data kernel. We present improvements of conventional lithospheric field modeling approaches to better determine the small-scale lithospheric field by incorporating gradient information.

Since the launch of GOCE in March 2009 until the re-entry in November 2013 about 42 months of gravity gradient data were collected, processed and distributed to the user community. Although the satellite life has come to an end, the exploitation of the GOCE data are still on-going and very interesting results from different disciplines are being generated. This paper focuses on describing which data are available and how they can be accessed: (1) Brief overview of release 5 of the GOCE gravity field models and access to the model data, (2) GOCE+ research program lates results and (3) GOCE de-orbiting data set description, analysis and access; (4) a presentation of all data tools available to access GOCE L1 and L2 data.

Longitudinal gradients in the auroral ionosphere are often neglected and the auroral arcs or, on a larger scale, the auroral oval, are frequently assumed to have 1D symmetry. However, at times, such gradients are presumably important. For example, the transition from 1D arcs along the quiet oval to the more complicated 2D aurora and back, during the substorm cycle, is likely to include stages when the 1D symmetry is not completely lost, though the longitudinal gradients matter. The Swarm mission provides an optimum platform to investigate these gradients, as well as the associated effects on auroral electrodynamics. With its two satellites, swA and swC, flying side by side some 30 km apart at auroral latitudes, and repeated instances when the third satellite, swB, crosses the auroral region simultaneously, at 100’s of km distance (increasing during the mission), Swarm can explore longitudinal gradients on a broad range of scales. Nonetheless, such an exploration faces various challenges, like the validation of the electric field data or the estimation of the ionospheric conductance, not measured on Swarm, from the electric and magnetic field observations. The paper will illustrate these challenges, as well as the required data adjustments and the derived longitudinal gradients.

The British Geological Survey is responsible for the fast-track magnetospheric field model product (MMA_2F), quick-look (MAG_QL and EFI_QL) and geomagnetic observatory data (AUX_OBS) products and L2 CAT-1 product validation, as part of the consortium of institutes making up the Swarm Expert Support Laboratory. We summarise these four activities and provide updates since presentations at the Paris Swarm Data Quality Workshop in September 2015.

The fast-track magnetospheric field model product is generated automatically on a daily basis at BGS after receipt of the Swarm L1b files, and delivered to ESA for onward public dissemination. As the time series of magnetospheric field estimates lengthens, long-term trends and patterns can be extracted. However careful account has to be taken of the effect of the separation in local time between the upper and lower satellites in this analysis.

The quick-look products are also generated automatically on a daily basis at BGS after receipt of the L1b files, but are delivered to ESA for internal use.

The observatory data product is updated every 3 months using a selection of definitive and quasi-definitive data from observatories around the world. Since Swarm was launched good quality data from about 120 observatories are available.

Validation comprises comparisons of Swarm-based models to independent models and data where possible, and inter-comparisons of models from the dedicated and comprehensive processing chains. A selection of plots from recent validation reports is given.

The ESA´s Earth Explorer mission Swarm is the third opportunity mission of the Living Planet programme. The magnetic field mission consists of three satellites Swarm A, B, and C. In addition to the main payloads for magnetic field observations the satellites carry an 8-channel GPS receiver and a Laser Retro Reflector for precise orbit determination.

As member of the Swarm Satellite Constellation Application and Research Facility (SCARF) TU Delft is providing the Level 2 orbit products for all three satellites. Additional Swarm orbit solutions are available from the Astronomical Institute of the University of Bern and from PosiTim UG. The three institutions are using three different software packages, namely GHOST, Bernese GNSS Software and NAPEOS. The external validation of the orbits with satellite laser ranging (SLR) measurements yields RMS values between 2 and 3 cm for the solutions from all three institutions. However, direct orbit comparisons show systematic offsets between the different solutions. In radial direction the orbit solutions from the different software packages show for instance systematic offsets of up to 1.2 cm.

The three software packages used for POD follow different approaches for the modelling of the non-gravitational forces acting on the satellite. In NAPEOS dynamical modelling is implemented to a large extent, in the Bernese GNSS Software empirical modelling is used and GHOST supports both possibilities. Therefore, erroneous information in the vector between the satellite´s center of mass and the GPS antenna phase center impacts the orbit solutions differently. As a result systematic orbit offsets are present between the solutions. However, systematic orbit offsets might also be caused by modelling deficiencies.

Results from the three different orbit determination approaches and the possibility to directly estimate the vector between the satellite´s center of mass and the GPS antenna phase center in NAPEOS might help to distinguish the causes of the systematic orbit offsets.

The main focus of this study are the radial offsets between the different Swarm orbit solutions. Studies with other satellites, e.g., Sentinel-1A, have shown that offsets in the radial direction are mainly caused by erroneous information whereas offsets in the other directions are more difficult to be distinguished. 

It has long been proposed that a specific distribution of field-aligned currents (FACs) would exist in association with the pulsating auroral patch. These FACs could arise locally as the closure of enhanced ionospheric currents within the patch, or in certain cases might be directly related to the pulsating auroral precipitation. However, previous studies on the FACs associated with pulsating aurora patches using ground magnetometers and/or low-Earth-orbit satellite data were often impeded by instrumental deficiencies such as the lack of spatial resolution or the uncertainty in determining FACs from single satellite passage. In this study, taking advantage of the side-by-side configuration of Swarm Alpha and Charlie satellites, we perform a survey of the quasi-DC (namely over a timescale of the on-time of the patch) FAC pattern associated with the pulsating auroral patches observed by THEMIS all-sky imagers. We found that, the patch-related FACs in general have a magnitude of order of a fraction of 1 uA/m², yet may occasionally reach >1 uA/m² in cases of bright and fast-moving auroral patches. The spatial distribution of the patch-associated FAC is contingent upon the MLT sector. In the postmidnight-morning sector where pulsating auroras are most often seen, the FAC tends to be upward in the west/south side of the patch, while downward in the east/north side of the patch. We interpret the observations in terms of the closure of ionospheric currents due to enhanced conductance led by the electron precipitation within the pulsating auroral patch. We also evaluate the possible effects of the patch-related current system on the local ionospheric electric field and on the drift motion of the pulsating auroral patch.

GOCE (Gravity field and steady-state Ocean Circulation Explorer) was the first satellite mission which combined SST-hl (Satellite-to-Satellite high-low) and SGG (Satellite Gravity Gradiometry) techniques to measure the Earth’s gravity field. During its lifetime, between 2009 and 2013, it delivered hundreds of millions of measurements. ESA published these observations so that the worldwide users can work with them in their scientific fields. In this study, we will present our latest GOCE-only global gravity field model, which is obtained from our own IfE software package.

We applied the acceleration approach to process the precise kinematic orbit data. The accelerations are computed from the satellite positions by numerical differentiation and they are balanced with the first derivatives of the gravitational potential. The functional model of the gravity gradients is set up in the GRF (Gradiometer Reference Frame) in which the gradients are directly linked to the second partial derivatives of the gravitational potential. Regarding the well-known low-frequency noise of the gradients, an empirical covariance matrix is estimated arc-wisely from the initial residuals and incorporated in the assembly of normal matrix in an iterative step. The full gravity field coefficients are finally solved in a joined analysis, in which the normal equation systems of the SST-hl and SGG analysis are combined by the Variance Component Estimation approach.

All the four years’ observations (from November 2009 to October 2013) are used for our latest solution, which is named as IfE_Goce05s. This gravity field model has a resolution with a maximum degree and order of 250, i.e. 62,997 unknown spherical harmonic coefficients had to be estimated. To evaluate our model, internal and external validation is carried out, e.g., degree error RMS comparison and using GPS leveling data set, etc. The comparison with the official GOCE models will be presented.

In this paper, we present a case study of structural mapping by applying the 3D Euler deconvolution method to the Bouguer data that was collected in the Southeastern Mediterranean and Northeastern Egypt regions. The solution obtained with 3D Euler deconvolution gives better-focused depth estimates, which are closer to the real position of sources; the results presented here can be used to constrain depth to active crustal structures (fault system, magmatic activity and subduction zones) for the study area.

The results indicated that the study area was affected by many sets of structural systems, which primarily trended in the NNE and NW directions (owing to the affect of Pelusium shear zone and differential motion of Africa and Arabia relative to Eurasia respectively). Minority of NNW structural system was expected to be found stronger in central Sinai and around Gulf of Suez region (with mean depth of 2- 4 km), which may attributed to the opening of Red Sea Rift System.

Nevertheless, the Cyprian arc region is dominated by several compressional fault systems of shallow depth analysis (0-4 km) trended E-W to WNW direction, which may initiated due to the northward-directed movement of Africa and ongoing subducting the Levant oceanic segment beneath the Tauric arc south of Cyprus.

Indeed, we find abrupt change depth values (1-8 km) almost clustered along the eastern segment of the Cyprian arc, Indicates continuation of the ophiolite at a depth below younger sediments of the Latakia and southern Antalya Basins. This means that, the Eratosthenes Seamount block is in the process of dynamically subsiding beneath Cyprus to the north and thrusted onto the Levantine Basin to the south.

The majority of deep Euler solutions values of Florence Rise area (6-8 km) are clustered on or near some active shear zones (Damietta–Latakia and Baltim–Hecateus Lines) which may attribute to stresses from magmatic activity.

However, the largest depth-estimates (2-12 km) connected with the volcanic intrusive bodies (intense magmatic activity) prevalent on continental crustal layer near Cairo-Suez District (Au Zaabal Basalt) which may exist due to current activity of Suez Rift and its extension to Eastern Desert and northern Cairo. These depths estimation were derived resulting different structural indexes (SI).

The main objective of our project is to study the signature of the Ultra Low Frequency (ULF) waves on the equatorial ionosphere. We will focus on monitoring the ULF-PC5 type and study its moduation to the equatorial electrodynamics. One of the drivers of equatorial ionospheric motion is the east– west electric field through vertical EXB drift, which is directly proportional to the equatorial electrojet (EEJ).

We will use the data from the SWARM satellite total electron content (TEC) measurments  to estimate the ionospheric density fluctuations, on the other hand, the EEJ will be estimated from the data of ground-based magnetometers in the equatorial region.

Our study will contribute to the recent scientific research effort demonstrate that Pc5 waves with a likely driver in the solar wind can penetrate to  the equatorial ionosphere and modulate the equatorial electrodynamics.

ESA’s very successful gravity mission GOCE (Gravity field and steady-state Ocean Circulation Explorer) orbited the Earth for exactly 1700 days (March 2009 to November 2013). During its lifetime approximately 42 months of data had effectively been collected with which the Earth’s gravity field can be determined in unprecedented accuracy and spatial resolution.

To ensure high quality for further use of the data (e.g. gravity field processing), data calibration and validation is carried out in the regular data processing. In addition to the standard processing chain people are working on further calibration and validation methods. In the framework of validation of the GOCE gravitational gradients at IfE Hannover, we work on two strategies for gradient in-orbit comparison. One is the comparison of measured gradients along collinear tracks, the second is the comparison of gradients in satellite track cross-overs.

This presentation focuses on the collinear track part and discusses the approach in some detail. Due to (a small) orbit eccentricity and satellite maneuvers, differences in altitude up to several kilometers occur between the tracks to be compared. As the gravitational gradient tensor is obtained from three-dimensional measurements, it depends on the instruments attitude which shows slight variations that have to be considered. The effect of both, differences in altitude and attitude, on the gradients has to be taken into account.

Here, we show selected results and especially illustrate the change of the gradients’ quality during the orbit lowering phase.

The GOCE satellite was launched in March, 2009 and its mission ended in November, 2013 with 1700 days of data. Its primary objective was to determine the stationary gravity field with a high accuracy of 1cm of geoid heights at spatial grid resolutions of 100km or less.  Exploitation of the satellite data acquired at an exceptionally low flying altitude of 255km, improved knowledge in several areas: gravity field models, oceanography, geodesy and solid Earth physics, which were among the main fields targeted by the mission. This was achieved thanks to the satellite’s payload consisting in a three-axis ultra-sensitive gradiometer. Each axis corresponds to a pair of accelerometers designed and built by ONERA which deliver the linear and angular accelerations acting on the satellite. From the measured linear accelerations and the evaluation of the spacecraft angular velocities, the terms of the gravity gradients matrix can be estimated. The in-flight data revealed that the noise level for the gravity gradient trace is twice higher than expected. Although this finding does not prevent the excellent performance of the mission, it led to an open question regarding the possible causes of the phenomenon. In order to investigate the plausible reasons of this finding, we propose to study the measurement noise for linear and angular accelerations during the mission lifetime for all axis and all accelerometers. We specifically look at the period extending from November 2^nd, 2009 to December 29^th, 2012.

In order to assess the noise of the accelerometers, we focus on the common modes instead of the differential modes. The differences of common modes, defined as the mean measurements of two accelerometers of the same pair, can serve as a proxy for instrument noise since theoretically, the signal should be null. This method cannot lead to assessments of individual accelerometer noises. However, if we assume that all accelerometers exhibit similar noise levels for Ultra Sensitive (US) axes, and we assume the same for the Low Sensitive (LS) axes, we can estimate upper bounds of the noise levels for these two types of axes. By combining different pairs in the difference of common modes, we can retrieve information about the noise levels for each axis.

We find that, in general, in the measurement bandwidth, the LS axes behave similarly and according to expectation, with a noise level slightly under the specifications. As far as the US axes are concerned, the noise level profiles are less homogeneous. It seems that for the pair of accelerometers aligned with the flight direction, the empirical noise follows the specifications closely in the measurement bandwidth. For the other US axes, the noise level is slightly higher than the specifications. In addition to this findings, we will also present the use of direct angular accelerations measurements to estimate the diagonal terms of the gradient gravity matrix.

The gravity missions GRACE (Gravity Recovery And Climate Experiment) and GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) have brought great improvements in the study of Earth Dynamic processes. Though they are very different in nature, the two missions provide very complementary gravity products, expressed in the form of spherical harmonic expansions. GOCE, a single satellite mission, relies on a very sensitive Electrostatic Gravity Gradiometer (EGG) composed of 6 accelerometers out of which 6 gravity gradients are computed, 4 of them sensitive enough to fulfill the mission requirement accuracy of 1-2 cm of geoid height at 100km spatial resolution. On the other hand, GRACE observations of the gravity field are based on a microwave ranging system with a few micron accuracy between its two satellites flying in formation. The complementarity of the two missions comes from the fact that GRACE gravity products have superior accuracy in the estimation of the low to medium degree terms, while GOCE prevails in the higher degrees. Several combination gravity fields – such as GGM05G, the GOCO’s and the EIGEN-6’s product families – already make use of this complementarity. However, detailed quality analysis of this products reveals characteristic errors in gravity fields resulting in North-South striations, or even small-scale bumpy patterns over the ocean. It is believed that the striations are likely to be attributed to the GRACE data at degree superior to 100 of the spherical harmonic expansion, while the bumpy pattern could be the results of non-optimal weighting at degrees where GRACE and GOCE’s accuracy are commensurate. The optimum weighting of each component in the estimation process is a key factor for producing high-quality gravity field. This paper discusses the GRACE and GOCE error modelling through the analysis of the correlations between model parameters and the impact of error sources such as measurement configuration and processing technique.

Gravity field and steady-state Ocean Circulation Explorer (GOCE) was the first satellite gravity gradiometry (SGG) mission. Extended life time and extremely low orbit resulted in very interesting and unique data. The aim of our contribution is to describe and investigate the statistical behaviour of particular elements of gravitational tensor measured by GOCE in terms of covariance functions. At first we focus on time series of SGG data collected along the orbit in gradiometer reference frame (GRF) and local north-oriented reference frame (LNOF) for 4 accurately measured elements. A one-parameter covariance function is used for this case. Differences between the covariance functions obtained from different parts of the orbit, different elements of the gravitation tensor and different mean altitudes are studied. Next, we take the full measurement cycle in several selected regions. Investigating the average dependency of gravitational tensor elements on horizontal distance and elevation difference we construct the empirical spatial covariance functions for selected regions. Empirical covariance functions are then fitted by convenient analytical functions. Our results are applied to interpolation of SGG data into a regular grid for chosen altitude and are compared with the grids produced from the GOCE-based global gravity field models. A question of optimal de-trending, non-stationarity and anisotropy of GOCE SGG data is discussed at the end of the contribution.

We explore how Swarm magnetic gradient and GOCE gravity gradient data can improve modelling of the Earth’s lithosphere and thereby contribute to a better understanding of Earth’s dynamic processes. We study the use of gradient grids to provide improved information about the lithosphere and upper mantle in the well-surveyed North-East Atlantic Margin. In particular, we present the computation of magnetic and gravity gradient grids at satellite altitude (roughly 450 km and 250 km above the Earth for Swarm and GOCE respectively). It is shown that regional solutions based on a tesseroid approach may contain more signal content than global models do. The patchwork of regional grids is presented as well as the subsequent error reduction through iterative downward and upward continuation using the Poisson integral equation. The promises and pitfalls are discussed of using grids at mean satellite altitude.

Swarm is a three-satellite magnetic mission of ESA, beside other instruments each satellite carries a GPS receiver for positioning and a space accelerometer for measuring  nongravitational forces. Unfortunately the accelerometer data has an unexpected and rather large temperature dependence. Using the on-board measured temperatures with a suitable phase shift this dependence can be reduced. To calibrate the accelerometer data, as the calibration standard one may use the GPS-orbits, from which the forces of gravity origin have been subtracted. We will show first results of this calibration procedure, where also the temperature dependence is taken into account.

The ESA Living Planet Programme successfully launched its fifth Earth explorer mission, Swarm, on 22 November 2013. Primary objective of this mission is to survey the Earth geomagnetic field and its temporal variation at unprecedented accuracy. Swarm can also be used to observe the Earth's changing gravity field and atmosphere. Swarm consists of three identical satellites flying as a constellation, where maneuvers are made to guarantee good coverage of the Earth.
All three satellites are equipped with dual-frequency, high-precision GPS receivers, which enable precise absolute orbit as well as baseline determination within this constellation. Nevertheless for baseline determination, interpolation needs to be firstly implemented to GPS observation files, in order to properly synchronize the time of three GPS receivers. The GPS observations are affected by the environment in which the satellites fly. For example, ionospheric scintillations lead to higher GPS observation residuals in especially the polar and equatorial regions, affecting orbit precision.
In this research, an extended Kalman filter considering differential spacecraft acceleration constraints is used to estimate orbital and other parameters for all Swarm satellites. Preliminary results indicate that the orbital performance of satellites differs as they are at different altitudes: in the selected period (Aug, 2014), Swarm-B was flying at 500 km altitude while Swarm-A and Swarm-C were flying in a pendulum-like formation at 470 Km altitude. The lower pair suffered more from ionospheric scintillations and  stronger atmospheric drag. The impact of improved modeling of solar radiation and Earth albedo will be studied as well.
The impact of two updates to the Kalman filter will be assessed. Firstly, a more comprehensive geometric spacecraft model replaces the simple cannon-ball model used so far for atmospheric drag and solar radiation estimation. It is anticipated that these updates will result in significantly smaller values for the estimated empirical acceleration. In addition, the so-called Phase Center Variation (PCV) and Code Residual Variation (CRV) maps are derived to improve the observation correction modeling and reduce observation residuals. Highlight here is the possibility of generating frequency-dependent maps from Kalman filter, allowing a frequency dependent correction of the observations.
Internal consistency and external validation are conducted to check the quality of the orbit solutions. It will be assessed if the Kalman filter updates lead to better consistency between kinematic and reduced-dynamic baseline solutions, and smaller carrier-phase and code observation residuals. Moreover, Swarm orbit solutions will be compared with external orbit solutions prepared by other institutes. Finally, the Swarm orbit solutions will be validated by comparison with Satellite Laser Ranging (SLR) observations.

The study of field-aligned current (FAC) sheets' motion is important for several reasons. It offers information about the dynamics of processes in the distant magnetospheric regions, magnetically connected with the auroral ionosphere. Then, by knowing the FAC sheets' orientation and velocity one can improve the existing FAC models, currently based solely on information about current sheet location. One can also assess the errors in FAC density estimation from single-satellite data, where the common assumption is to neglect the sheet motion during FAC crossing.

The present paper will address the problem of FAC motion based on data provided by the ESA multi-satellite Swarm mission. The study has some peculiarities. On the one hand, the Swarm orbital motion poses one significant challenge: Typical values of the FAC sheet normal velocity are at the order of a few 100 m/s at ionosphere altitude. With a time separation between the two satellites flying side-by-side, swA and swC, ranging roughly between 7 and 11 s, and an orbital velocity of about 8 km/s, in order to properly derive the FAC velocity, the required precision in the timing information is of the order of 0.1 sec. On the other hand, every few days the Swarm spacecraft form a close constellation in the polar region and the estimation of FAC motion can also take advantage of the measurements provided by the third Swarm satellite, swB. A few FAC crossings by Swarm will be presented to illustrate the key points of the study.

The Swarm satellites were launched on 22 November 2013 and carry accelerometers and GPS receivers as part of their scientific payload. The GPS receivers are not only used for locating the position and time of the magnetic measurements, but also for determining non-gravitational forces like drag and radiation pressure acting on the spacecraft. The accelerometers measure these forces directly, at much finer resolution than the GPS receivers, from which thermospheric neutral densities and potentially winds can be derived. Unfortunately, the acceleration measurements suffer from a variety of disturbances, the most prominent being slow temperature-induced bias variations and sudden bias changes. These disturbances have caused a significant delay of the accelerometer data release.

In this presentation, we describe the new, improved four-stage processing that is required for transforming the disturbed acceleration measurements into scientifically valuable thermospheric neutral densities. In the first stage, the sudden bias changes in the acceleration measurements are manually removed using a dedicated software tool. The second stage is the calibration of the accelerometer measurements against the non-gravitational accelerations derived from the GPS receiver, which includes the correction for the slow temperature-induced bias variations. The identification of validity periods for calibration and correction parameters is part of the second stage. In the third stage, the calibrated and corrected accelerations a merged with the non-gravitational accelerations derived from the GPS receiver by a weighted average in the spectral domain, where the weights depend on the frequency. The fourth stage consists of transforming the corrected and calibrated accelerations into thermospheric neutral densities. We describe the methods used in each stage, highlight the difficulties encountered, and comment on the quality of the thermospheric neutral density data set.

The Swarm mission, launched in November 2013, consists of three identical satellites designed to measure the magnetic field in space to the highest resolution ever. One of the Swarm mission’s unique aspects is the ability to measure the magnetic field at approximately the same position using two satellites (A and C) which travel almost behind one another at the same altitude. In addition, using the measurement of the gradient of the field between the satellites removes much of the external field’s influence in the data, leaving the contribution from the steady internal field, each time the satellites pass over the same location. In combination with measurements of the satellite along-track differences this adds a new capability that can be exploited to produce magnetic field models of the lithospheric field with higher accuracy than before.

We produce a lithospheric field model using Swarm along track and gradient data and use it to improve on the previous models based on CHAMP data alone, following the methodology of Olsen et al. (2015) for example. In addition, we apply Slepian functions to examine the spectral content of the oceanic and continental basins, to see if the improved lithospheric models show differences with previous iterations.

References:

Olsen, Nils, et al. "The Swarm Initial Field Model for the 2014 geomagnetic field." Geophysical Research Letters 42.4 (2015): 1092-1098.

The Earth’s Magnetic Field and Environment Explorers (Swarm), launched in November 2013, aim at improving the knowledge of the geomagnetic field. Nevertheless, the data gathered by the Global Positioning System (GPS) and star tracker instruments are also useful for geodetic applications, in particular to measure large-scale temporal variations of Earth’s gravity field.

The GRACE satellites are expected to stop gathering data in the near future, despite the efforts that have been made to prolong the mission lifetime (Herman, 2012). As a consequence of the requirement to continue monitoring the Earth system, a GRACE Follow-On (GRACE-FO) mission (Sheard et al. 2012; GRACE-FO/JPL 2015; GRACE-FO/GFZ 2015) is currently already under implementation and due for launch in August 2017. To keep the time series of gravity field models uninterrupted in the possible gap between these two gravimetric missions, alternative data must be used. Using High-low Satellite-to-Satellite tracking (hl-SST) data, such as from the Swarm satellites, is a good option in order to derive at least the long-wavelength features of the Earth’s gravity field variations as demonstrated by Weigelt et al. (2013) and Baur (2013).

A number of institutes have produced gravity field models from Swarm, with different approaches and reporting different accuracies. The gravity field solutions relevant to this study are those produced by the Astronomical Institute (ASU) of the Czech Academy of Sciences (Bezděk et al., 2014), the Astronomical Institute of the University of Bern (AIUB)(Jäggi et al., 2015) and the Institute of Geodesy (IfG) of the Graz University of Technology (Zehentner et al., 2015). Although these models represent surface mass changes over large basins accurately, there is still some room for improvement, to the benefit of the geophysical studies that exploit these data. We propose to combine the various solutions in a statistically optimal way, similarly to the approach taken by the European Gravity Service for Improved Emergency Management project (http://egsiem.eu), concerning GRACE and other satellite missions. In this way, the strengths of one method compensate for the weaknesses of another.

References:

O. Baur. Greenland mass variation from time-variable gravity in the absence of GRACE. Geophysical Research Letters, 40(16):4289–4293, August 2013. ISSN 00948276. DOI 10.1002/grl.50881.

Bezděk A, Sebera J, Klokočník J, Kostelecký J, 2014. Gravity field models from kinematic orbits of CHAMP, GRACE and GOCE satellites. Advances in Space Research 53, 412–429. http://dx.doi.org/10.1016/j.asr.2013.11.031

Gravity Recovery and Climate Experiment-Follow-On (GRACE-FO) Mission. 10/06/2015. GFZ German Research Centre for Geosciences. Accessed 10/2015. URL https://www.gfz-potsdam.de/en/grace-fo

Jaap Herman. Balancing, Turning, Saving Special AOCS Operations to extend the GRACE Mission. In SpaceOps 2012 Conference, Reston, Virgina, June 2012. American Institute of Aeronautics and Astronautics. DOI 10.2514/6.2012-1275114.

Jäggi, A., C. Dahle, D. Arnold, H. Bock, U. Meyer, G. Beutler, J. van den IJssel; 2015: Swarm kinematic orbits and gravity fields from 18 months of GPS data. Advances in Space Research, under minor review.

Missions | Gravity Recovery and Climate Experiment Follow-on. 2015. Jet Propulsion Laboratory, California Institute of Technology. URL http://www.jpl.nasa.gov/missions/gravity-recovery-and-climate-experiment-follow-on-grace-fo/

B. S. Sheard, G. Heinzel, K. Danzmann, D. a. Shaddock, W. M. Klipstein, and W. M. Folkner. Intersatellite laser ranging instrument for the GRACE follow-on mission. Journal of Geodesy, May 2012. ISSN 0949-7714. DOI 10.1007/s00190-012- 0566-3.

M. Weigelt, T. van Dam, A. Jäggi, L. Prange, M. J. Tourian, W. Keller, and N. Sneeuw. Time-variable gravity signal in Greenland revealed by high-low satellite-to-satellite tracking. Journal of Geophysical Research: Solid Earth, 118(7):3848– 3859, July 2013. ISSN 21699313. DOI 10.1002/jgrb.50283.

N. Zehentner, T. Mayer-Gürr, Performance of Swarm Satellites as gravity probes, presented at the 26^th IUGG General Assembly 2015, Prague, Czech Republic, http://www.czech-in.org/cmdownload/IUGG2015/presentations/IUGG-3296.pdf

The aim of this work is to study how sensitive satellite magnetic field measurements are to the large-scale thermal state and composition of the lithosphere. There is a direct relation between the magnetic field and temperature, because magnetization cannot persist at a temperature higher than the Curie temperature. Therefore the long-wavelength part of magnetic anomalies is controlled by temperature.

It is commonly assumed that magnetisation is limited to the crust because mantle rocks are not magnetic. However, this is a topic of recent controversial discussion.  Firstly, different minerals are responsible for rock magnetization/susceptibility. Therefore, there are several Curie depths, one for each mineral. Also, this implies that rock magnetization is affected by composition in addition to temperature. Secondly, petrologic evidence suggests that mantle rocks may, in fact, contain magnetic minerals. Thus, the uppermost mantle might have an effect on the magnetic field, at least in relatively cool areas.

To test whether Swarm data can help to clear up some of these controversies, we estimated the global temperature distribution within the lithosphere. This was done by assuming that temperature transport within the lithosphere is purely by conduction. We then estimated Curie depth using lithospheric thickness from Litho1.0 and surface heat flow data.

Our approach requires good knowledge of lithospheric structure, which is normally provided by seismological methods. However, high quality seismologic surveys cover only a small part of the Earth’s surface. Satellite gravity data provide additional constraints that supplement seismologic information, even in areas without seismic coverage.

We studied the interplay of seismologic information and gravity using a seismological model of the North American continent. Several continental seismic profiles have been shot in North America during the last decades, providing good knowledge of crustal structure. Still, the gravity field predicted by this model is inconsistent with observed free air gravity. This is partially explained by density anomalies below the crust. However, analysis of the gravity gradients provided by GOCE suggests the misfit originates from within the crust as well.

The rapid dynamics of the core are largely unknown; the mantle and crust filter and mask small-scale spatial and temporal features and field sources external to the Earth contaminate the observations we have. Geomagnetic jerks represent the most rapid observed variations of the internal field, on the scale of months--years and, after nearly 40 years of study, their origins still remain somewhat elusive. Jerks are rapid changes between periods of an otherwise approximately linear rate of change of the main field. In the simplest approximation jerks are `v' or `^' shapes in the first time derivative of the main field --- the secular variation --- and step changes in the second derivative --- the secular acceleration. Recent analysis of quasi-definitive observatory data by Torta et al. [2015] has suggested a jerk occurred at 2014.0. This jerk comes after several similar jerks during the 2000s, concurrent with the rise and fall of secular acceleration power at the core-mantle boundary around a series of peaks, the most recent in 2012.5, identified by Chulliat et al. [2015].

With the rapid provision of Swarm satellite observations and auxiliary observatory measurements, it is possible to rapidly construct up-to-date models of the geomagnetic main field and its time variations. We derive such a model based on Swarm data and investigate the occurrence and spatiotemporal characteristics of jerks in the recent period, at both the core-mantle-boundary and the Earth's surface. Torta et al. [2015] suggest that global models show regions of high secular acceleration associated with the 2014.0 jerk may be seen at European observatories from 2014 onward. Since this region is densely covered by the surface observatory network as well as Swarm orbits, a more detailed view of geomagnetic variations may be possible.

We also comment on early and potential future discrepancies between IGRF-12 predictions and observations in the period of 2015-2020 as a result of the unpredictable non-linear secular variation of jerks.

References

Chulliat, A., P. Alken, and S. Maus (2015), Fast equatorial waves propagating at the top of the Earth's core, Geophys. Res. Lett., 42, doi:10.1002/2015GL064067.

Torta, J. M., F. J. Pavón-Carrasco, S. Marsal, and C. C. Finlay (2015), Evidence for a new geomagnetic jerk in 2014, Geophys. Res. Lett., 42, doi:10.1002/2015GL065501.

Data from the Cryosat-2 (369 days repeat mission) as well as Jason-1 end-of-life mission are the first new “geodetic mission” data sets released in nearly 2 decades since the ERS-1 and Geosat geodetic missions were conducted in the early 90’th and late 80’th.  

Besides providing high quality sea surface height observations, the Cryosat-2 has now  completed its fifth cycle of 369 days. This opens for new ways of using “pseudo” repeat Geodetic mission data, by averaging or other means of analysis

One further advantage of the Cryosat-2 is its ability of provide new accurate sea surface height information for gravity field determination in the northernmost part of the Arctic Ocean upto 88N where no altimeters have measured before.

The first evaluation of the DTU15 global marine gravity field is presented here. The DTU15 is  based on five years of retracked altimetry from Cryosat-2 as well as data from the Jason-2 EOL geodetic missions. It is shown how the older geodetic missions (ERS-1 and GEOSAT) only contribute valuable information in very limited regions of the world.

In the Arctic Ocean are testing an new combined empirical/physical retracking system that uses physical retracking of the LRM data using a reduced parameter system in combination with empirical retracking of the SAR and SAR-In data in particularly high latitude regions.

The new high resolution global marine free air gravity field called DTU15 is presented in this presentation. Data from the Cryosat-2 (369 days repeat mission) as well as Jason-1 end-of-life mission are the first new “geodetic mission” data sets released in nearly 2 decades since the ERS-1 and Geosat geodetic missions were conducted in the early 90’th and late 80’th

The DTU15 global marine gravity field, is based on five years of retracked altimetry from Cryosat-2 as well as data from the three other geodetic missions (ERS-1, GEOSAT and Jason-1). However, the older geodetic missions ERS1 and GEOSAT only provide marginal additional information in very limited regions.

In the Arctic Ocean are testing an new combined empirical/physical retracking system that uses physical retracking of the LRM data using a reduced parameter system in combination with empirical retracking of the SAR and SAR-In data in particularly high latitude regions.

An advantage of the Cryosat-2 is its ability of provide new accurate sea surface height information for gravity field determination in the northernmost part of the Arctic Ocean upto 88N where no altimeters have measured before.

The DTU15MSS is the latest release of the global high resolution mean sea surface from DTU Space. The major new advance leading up to the release of this DTU15MSS the use of an improved 4 years Cryosat-2 LRM, SAR and SAR-In data record and the downweighting of ICESat data used previously in the Arctic Ocean for DTU10MSS and DTU13MSS.

A new reference surface for off-shore vertical referencing is introduced. This is called the DTU15LAT.

The surface is derived from the DTU15MSS and the DTU10 Global ocean tide to give a 19 year Lowest Astronomical Tide referenced to either the Mean sea surface or to the reference Ellipsoid via the use of the DTU15MSS.

The presentation will also focus on the difficult issues as consolidating Cryosat-2 onto a 20 year mean sea surface derived using multiple satellites (but only at low to medium latitude) as well as the importance of merging Cryosat-2 data from different operating modes like LRM, SAR and SAR-In as these requires different retrackers. Also the importance of downweighting the ICESat data is highlighted.

Ionosphere is a time varying, inhomogeneous, anisotropic and spatio-temporally dispersive medium whose descriptive properties can be estimated using indirect measurements. The variability of ionosphere can result from solar, geomagnetic, gravitational or seismic activities. This complex spatio-temporal variability is very difficult to be identified due to extensive scales in amplitude, duration, period and frequency of disturbances. The random field model of ionosphere, which is made up of a trend component and a variability component, can be related to various solar and geomagnetic indices such as Sun Spot Number (SSN), F10.7 solar flux, Disturbance storm time (Dst), Auroral Electrojet (AE), Kp and W-index. Since most of these indices are estimated or predicted to indicate the ionospheric activity at different parts of the Earth or they indicate global disturbance, it is highly complicated to identify and classify regional disturbances.

One of the major descriptors of the ionosphere, the Total Electron Content (TEC) can be estimated from GPS receivers and the derived Global Electron Content (GEC) can be used to model the regional and local variability that differs from the global activity along with the solar/geomagnetic indices and W-index. In this study, by using machine learning techniques, such as Artificial Neural Networks (ANN) and Support Vector Machines (SVM), robust regional disturbance indices will be developed. The ionospheric disturbance levels characterized by the developed indices will be compared with the estimated disturbance levels based on the IRI-Plas-2015 model to generate the discrepancy between the trend and the actual ionospheric state. Based on the observed discrepancy, our aim is to classify the regional effects of the global geomagnetic storms and classify them according to their risk levels. Also, we will investigate whether it is possible to differentiate the disturbances generated by the local seismic precursors from those generated by geomagnetic or gravitational anomalies. The technique will be demonstrated for the mid-latitude ionosphere over the Turkish National Permanent GPS Network (TNPGN-Active) for the solar maximum year of 2011.

This study is sported by the joint TUBITAK 114E541 and AS CR 14/001.

The GOCE satellite mission has brought a significant improvement in modelling of the low-frequency part of the Earth’s static gravity field. The recent GOCE-based satellite-only geopotential models provide a valuable basis for a unification of height systems. They are fully independent from local vertical datums, however, they are affected by a stripping noise due to the omission error of the spherical harmonics approach. Consequently, the satellite-only mean dynamic topography (MDT) obtained as a combination of such models and mean sea surface models provided by satellite altimetry are also significantly affected by the stripping noise which needs to be reduced.

In this study we use the nonlinear diffusion filtering to reduce the stripping noise of the satellite-only MDT generated from the GO_CONS_GCF_2_DIR_R5 geopotential model and the DTU13 mean sea surface model. Before filtering, a special effort is made to prolong information from the satellite-only MDT model towards coastlines and continents. Such an augmented MDT model filtered by the nonlinear filtering is used to interpolate its values along the coastline or at tide gauges. These values are less affected by the stripping noise and thus can provide more reliable estimates of offsets between tide gauges as well as their relation to the selected W0 value as a reference level for an establishment of the World Height System.

ESA has recently released a study on the potential of ocean levelling as a novel approach to the study of height system unification taking the recent development in geoid accuracy trough GOCE data into account. The suggested investigation involves the use of measurements and modelling to estimate Mean Dynamic Topography (MDT) of the ocean along a coastline which contributes/requires reconciling altimetry, tide gauge and vertical land motion. The fundamental use of the MDT computed using altimetry, ocean models or through the use of tide gauges has values of between -2 and +1 meters at different points in the ocean. However, close to the coast the determination of the MDT is problematic due to i.e., the altimeter footprint, land motion or parameterization/modelling of coastal currents.

The objective of this activity is to perform a consolidated and improved understanding and modelling of coastal processes and physics responsible for sea level changes on various temporal/spatial scales. The study runs from October 2015 to march 2017 and involves elements like: Develop an approach to estimate a consistent DT at tide gauges, coastal areas, and open ocean; Validate the approach in well-surveyed areas where DT can be determined at tide gauges; Determine a consistent MDT using GOCE with consistent error covariance fields; Connect measurements of a global set of tide gauges and investigate trends

Swarm Payload Data Ground Segment: Status and Evolution Plans

Swarm is the fifth ESA Earth Explorer mission which was successfully launched on 22 November 2013. The main scientific objectives of the Swarm mission are to provide the best-ever survey of the geomagnetic field and its temporal evolution as well as the electric field in the atmosphere, using a constellation of three identical satellites.

The Swarm Payload Data Ground Segment (PDGS) is the mission's element in charge of the data processing, archiving, and dissemination; products quality control; and calibration and performance monitoring. The Swarm PDGS functionalities are implemented as a combination of dedicated systems and teams, and shared services. It has been working without major problems since the launch, and the Transfer To routine Operations (TTO) was completed in January 2015.

This poster provides an overview of the current status of the Swarm PDGS and the evolution plans, highlighting the aspects more relevant to the end-users as the processing status and forthcoming updates, datasets release outline, planned reprocessing campaigns, and user data access.

We develop new nonlinear diffusion filtering method on closed surfaces such as Earth topography or satellite orbits. Our new model extends the regularized surface Perona-Malik model by including local extrema detector based on the mean curvature of processed data. The model is thus represented by a nonlinear diffusion equation which at the same time reduces noise and preserves main edges, local extrema and details important for a correct interpretation of real geodetic data. We define a surface finite-volume method to approximate numerically the nonlinear parabolic partial differential equation on a closed surface. The closed surface is approximated by a polyhedral surface created by planar triangles and we use a piece-wise linear approximation of the solution in space and the backward Euler time discretization. We present numerical experiments related to nonlinear diffusion filtering of GOCE measurements and satellite-only mean dynamic topography data.

Ionospheric and thermospheric storms are strong perturbations in the ionosphere and thermosphere caused by the significant variations in the magnetic activity. In this work, we use a set of multiple ground-based and space-borne instruments to study the ionospheric and thermospheric responses to the recent geomagnetic storms. The multi-instrumental approach, and especially the use of data of the recent satellite missions, such as GRACE, CHAMP, GOCE, Swarm, etc., has already proved to be useful in finding new aspects of the global distribution of the upper atmosphere plasma with unprecedented detail. One of the most interesting recent findings is the demonstration of an altitudinal difference of the ionospheric behavior during geomagnetic storms, and occurrence of intensive ionospheric irregularities in the topside ionosphere (above the ionization maximum). In our contribution, we show several examples of the multi-instrumental (from ground-based and space-borne instruments) analysis of the ionospheric and thermospheric effects during geomagnetic storms occurred within the last solar cycle.

Several space-plasma media are characterized by turbulent fluctuations covering a wide range of temporal and spatial scales from the MHD domain down the kinetic region, which substantially affect the overall dynamics of these media. In the framework of ionosphere-magnetosphere coupling, magnetic and plasma disturbances are driven by different current systems resposible for the coupling. These disturbances manifest in the plasma parameter inhomogeneity and in the magnetic field fluctuations, which are capable of affecting the ionospheric conditions. Furthermore, the study of ionospheric plasma irregularities and turbulence is of particular interest for space weather applications. The present work focuses on the analysis of the statistical features of magnetic and plasma fluctuations in different ionospheric regions at Swarm altitude.The multi-satellite mission, Swarm, is equipped with several instruments which observe electromagnetic and ionospheric parameters of the near-Earth space environment. Using these data we investigate the shape of the probability distribution functions of the fluctuations in the polar and equatorial ionospheric regions, and analyze the correlation between magnetic and plasma fluctuations using information theory approach. The aim of this work is to characterize the different features of ionospheric plasma turbulence driven by magnetospheric dynamics and to discuss the results in the framework of Sun-Earth relationship and space weather.

At present state, one of the most frequent use of global geopotential models concerns local W0 value computation. Most of the studies employ the Earth Gravitational Model 2008 (EGM2008) for the task on mean gravity or surface gravity potential computation needed in order W0 to be obtained. Only recently there are a few studies that make use of the latest satellite-only models with GOCE data for the same purpose. Considering the fact that satellite-only models do not have the spectral resolution of the ultra-high degree EGM08 it might be of advantage to benefit from a local gravity or GPS/levelling dataset for validating the satellite-only model and then investigate the impact on a W0 value.

Thus the current study aims to assess the performance of various GOCE-based gravity field models (GGMs) for W0 computation over the territory of Bulgaria. The EGM2008 is also added to the list of tested models in order to get reference with previous research. As a first step all GGMs are validated using a local gravity anomaly dataset of more than 282 000 unequally distributed gravity points. A comparison based on simple statistics (min, max and standard deviation values) is presented and discussed. Afterwards, the models are validated externally in terms of independent set of geoid heights from GPS/levelling over the Bulgarian territory. The obtained results are compared against previous research; that shed some light on the local gravity field improvement brought by GOCE data. Then, the best fitted and worst fitted two models are used for W0 computation in order to investigate the variations of local W0 value and its uncertainty due to the performance of the GGMs. Two independent methods of W0 computation with different sensitivity to the quality and quantity of the data are used. Results of a preliminary study suggest that a difference of about 0.3 - 0.4 m²/s² in the derived W0 values depending on the implemented method of computation should be expected. Also, the quantity-dependent method is likely to give better W0 uncertainty estimates when the last realizations of the GGMs are used. Furthermore, a comparison between the two pairs of W0 values (with the best fitted and worst fitted to the GPS/levelling models) presents the GGMs’ performance improvement: the difference in the W0 values due the implementation of the earliest GGM realizations is around 0.35 m²/s², and the application of the last realizations produces rather similar W0 value despite the model used.

In addition, similar W0 computations have been performed and compared with non-validated GGMs in order to examine the impact of the validation in such case studies.

With some further considerations one local W0 value for Bulgaria could be recommended to be used in the future for the modernization of the National Height System of Bulgaria.

Until now, monthly GRACE gravity field models have been available with a time delay of about two months, which just allows for the ‘confirmation after occurrence’ and to assess the severity of a hydrological extreme event. As part of the EGSIEM (European Gravity Service for Improved Emergency Management) project, a technology demonstrator for a near real-time (NRT) gravity field service will be established, with the goal of reducing this latency to a maximum of five days and to provide daily gravity field models. These rapid gravity time series will enable us to monitor the global water storage in NRT and to observe floods and droughts as they occur. This information will help rapid mapping providers to react earlier to such hydrological events, resulting in improved emergency and assistance efforts. As basis of the daily gravity field recovery serves a Kalman filter framework, in which GRACE data is combined with prior information to increase the redundancy of the gravity field estimates. The Institute of Geodesy at Graz University of Technology (TU Graz) routinely processes daily gravity field time series in post-processing as part of static gravity field releases. In preparation of the operational phase of the service, several aspects of this processing chain have been inspected in order to improve the gravity field solutions and move towards NRT.

This contribution summarizes the results of the first project phase at TU Graz on the basis of a new daily gravity field time series. We present an improved stochastic state-space model, derived from empirical covariance estimates of geophysical model output and evaluate its performance using in-situ measurements as well as GRACE range-rate residuals. To satisfy the maximum time delay of five days, forward-backward smoothing as is used in the standard post-processing chain, has been replaced by an on-line smoothing algorithm. The effect of this novel state estimator is investigated by comparison of the computed time series with post-processing and forward-only filtered solutions. From the results of this evaluation we determine the error levels which can be expected from the near real-time gravity field estimates.

Computerized Ionospheric Tomography (CIT) is an essential tool to reconstruct highly varying, inhomogeneous and anisotropic magnetoplasma. Typically in the literature, ionospheric electron density reconstruction is performed using satellite signals that cross ionosphere on designated tracks. The most efficient of these satellite systems is Global Positioning System (GPS) constellation. The signals that are refracted and delayed in the ionosphere carry information on the Slant Total Electron Content (STEC) which can be estimated from earth based dual-frequency GPS receivers. STEC is the line integral of electron density values between the GPS receiver and satellite and this value corresponds to the total number of electrons on this ray path. Using a network of GPS receivers, the electron density profile in the vertical direction can be reconstructed using various tomographic techniques. Unfortunately, the sparsity of the measurement data, fixed tracks and passage durations of satellites increase the computational complexity and reduce the efficiency and accuracy of most numerical reconstruction methods. Recently, a novel ionospheric tomography technique, namely IONOLAB-CIT, is proposed to overcome the efficiency and accuracy problems. IONOLAB-CIT is a regional tomographic reconstruction technique which is based on 3-D ionospheric electron density structure obtained from International Reference Ionosphere Extended to Plasmasphere (IRI-Plas) model. IRI-Plas can input external values for critical frequency and height of maximum ionization layer of ionosphere, foF2 and hmF2, respectively. The developed technique forms planar perturbation surfaces for foF2 and hmF2, and updates these surfaces at each iteration level using the difference of GPS-STEC and IRI-Plas-STEC. In this study, this novel tomography algorithm, IONOLAB-CIT is applied to Central Europe using IGS and EUREF GPS stations for successful reconstruction of vertical electron density profiles. The validation of the algorithm is demonstrated by the comparison of IONOLAB-CIT results with the electron density profiles obtained from ionosonde stations in that region, such as Juliusruh and Pruhonice. It is observed that IONOLAB-CIT can successfully reconstruct electron density profiles for both quiet and disturbed days of the ionosphere.

This study is supported by the joint TUBITAK 112E568 and RFBR 13-02-91370-CT and joint TUBITAK 114E092 and AS CR 14/001 projects.

ESA's Swarm satellites carry ⁴He absolute magnetometers (ASM), designed by CEA-Léti and developed in partnership with CNES. These instruments are the first-ever space-borne magnetometers to use a common sensor to simultaneously deliver 1Hz independent absolute scalar and vector readings of the magnetic field. They have provided the very high accuracy scalar field data nominally required by the mission (for both science and calibration purposes, since each satellite also carries a low noise high frequency fluxgate magnetometer designed by DTU), but also very useful experimental absolute vector data. They have also been run for short periods of time in a so-called burst mode to deliver absolute scalar data at 250 Hz. In this presentation, we will report on the various tests and investigations carried out using these data since launch in November 2013. In particular, we will illustrate the advantages of flying ASM instruments on space-borne magnetic missions for data quality checks, geomagnetic field modeling and science objectives.

Towards an utilization of the 'Swarm'-constellation,  the use of in-track and cross-track data had come into focus and had already proved usefullness by the DTU modeling group.  As it had shown to be able  to reduce the influence of spurious external fields we aim to assess the improvements of the modeling of the features of secular variation (SV); in particular, if this methods allow the use of shorter time periods or granting higher complexity in the representation of variations.  We aim to compare those constellation driven advantages  with available models with respect to the sensitivity to short-term changes.

Swarm is the first ESA Earth Observation Mission with three satellites flying in a semi-controlled constellation. The trio is operated from ESA’s satellite control center ESOC in Darmstadt, Germany. The Swarm Flight Operations Segment consists of the typical elements of a satellite control system at ESOC, but had to be carefully tailored for this innovative mission. The main challenge was the multi-satellite system of Swarm, which necessitated the development of a Mission Control System with a multi-domain functionality, both in hardware and software and covering real-time and backup domains. This was driven by the need for extreme flexibility for constellation operations and parallel activities.

Commanding is supported by a complex Mission Planning System which generates two command schedules. The first contains commands to be send in real time and is typically related to automated pass operations by setting up the link configurations to the respective Ground Station. The other provides time-tagged telecommands to be loaded into the satellite Mission Timeline and controls mainly the critical data downlink strategy. This is based on just two Ground Station passes per satellite and day and ensures that always up to three days’ worth of science data are available onboard for re-dump (fill status of science packet store up to 70%).

The three months of commissioning in 2014 were characterised by a very tight and dynamically changing schedule of activities. All operational issues could be solved during that time, including the challenging orbit acquisition phase to achieve the final constellation. About 40% of the originally available fuel was consumed for these manoeuvres. Since then the onboard fuel is spend for normal attitude maintenance (up to 15g/week of more than 60kg Freon still available per satellite), constellation correction manoeuvres for Swarm-A and special payload related tests requiring attitude thruster activations.

The latter included several attitude slews which also effected the temperature at the satellite RAM Face where the Electrical Field Instrument (EFI) is located. Slew manoeuvres were for instance performed in May 2014 to characterise the observed residuals of the two magnetometers VFM and ASM.

Although the actual spacecraft commissioning phase was concluded in spring 2014, the investigations for some payload instruments continue until now. The EFIs are still being tested in order to characterize and improve science data quality. Changing duty rates of EFI nominal operations and frequent onboard parameter updates different for all satellites still cause a high workload for all involved parties and reduce the percentage of useful data during routine phase.

Various test phases became also necessary for the Accelerometers (ACC) on the Swarm satellites. This included changes of thermal set-points in May and August 2015 in order to reduce unwanted thermal perturbations within the instruments. Test campaigns with attitude thruster activations were conducted to deduce ACC scale factors needed to adjust accelerometer deviations for all satellites.

In order to improve the performance of the GPS Receivers for better scientific exploitation and to minimise the failures due to loss of synchronisation, a number of parameter changes were commanded via onboard patches, including a stepwise increase of the GPS field-of-view to now 88º.

Finally, to minimize the impact on operations, a new strategy had to be implemented to handle single/multi bit errors in the onboard mass memories (MMU), defining when to ignore and when to restore the memory via a MMU recovery.

The poster presentation summarizes the Swarm specific ground segment elements of the FOS and explains some of the extended payload commissioning operations, turning Swarm into a most demanding and challenging mission for the Flight Control Team at ESOC.

The whole dataset acquired by the GOCE mission, from November 2009 to October 2013, has been processed by the space-wise approach. The observation period, corresponding to about one hundred million epochs of valid data, includes both the mission phase at nominal satellite altitude of about 255 km and the orbit lowering phase when the satellite slowly went down to about 224 km. Before the processing, subsets of uninterrupted observations with a consistent in-flight calibration have been defined and outliers have been detected and possibly repaired to preserve the stochastic characteristics of the signal. This is crucial to get a satisfactory result. Afterwards the space-wise approach is applied to produce the final global grids of the gravity gradients at 0.2°x0.2° resolution.

This approach is based on iterative steps designed to filter the noise and reduce the spatial correlation of the data, both in the time domain, namely along the orbit, by taking into account the time correlation of the observation noise, and in the space domain by exploiting the spatial correlation of the gravity field. The first step is the SST data processing by the energy conservation approach to estimate the low degrees of the gravity field, which are used as input for the SGG data processing. This consists in different filtering-gridding steps dedicated to different parts of the harmonic spectrum: in particular, a Wiener filter is first used to enhance the medium degrees of the gravity field, while a White filter is then applied to recover the high degree information carried by GOCE observations. Each filtering phase is coupled with a local collocation gridding procedure, the former using large patches, the latter using more localized ones; in both cases, the signal covariance is adapted on the local characteristics of the patch.

The output grids are delivered together with their associated error standard deviations, which are computed by Monte Carlo simulations. Moreover, from the grids a set of spherical harmonic coefficients is straightforwardly derived by numerical integration and global regularization, together with the corresponding full error covariance matrix. The information content of the obtained results is assessed by comparing them with other global grids and spherical harmonic models.

The availability of two years of magnetic data from Swarm satellites allows their direct comparison with data from ground observatories. Even if a longer time span would be preferable for this purpose, available data are sufficient to gain interesting information.

So, after selecting a number of magnetic ground observatories, for each observatory we compare directly ground measurements with those made onboard Swarm satellites when flying within a cylinder centred at each observatory. Then, we reconstruct at the same locations, the so-called virtual magnetic observatories following the approach proposed by Mandea and Olsen (GRL, 2006) who used Champ measurements to recover monthly means of X, Y and Z Cartesian components of the Earth’s magnetic field to study its secular variation over short timescales.

Results obtained using data from Swarm Alpha, Bravo and Charlie are discussed in terms of the altitude and of the geographical location of the reconstructed virtual observatories.

With the GRACE mission, the mapping of the time-variable gravitational field has proved to be a key element for the study of the Earth’s global mass transport. Consequently, there is a strong demand from the Earth science community for a continuous monitoring of the gravitational field, with an even better spatial and temporal resolution.  As a result, a follow-on, GRACE-FO, is already scheduled for 2017 while new gravity mission concepts and technologies with potentially improved performances are being developed. Most of these concepts are based, like GRACE, on inter-satellite ranging and high-low satellite-to-satellite tracking. Here, we investigate the potential of optical gradiometry for time-variable gravitational field mapping.

An optical gradiometer measures, thanks to a laser interferometer, the variations of the distance between 2 close, free-falling test-masses. From this measurement and together with the angular rates of the gradiometer frame, it is possible to retrieve the gravitational gradient signal. In this study, we first analyse the instrumental constraints and put forward the “suspension mode” as the best operational and feasible configuration for the gradiometer. In the suspension mode, the test masses are kept as inertial as possible only in a limited measurement bandwidth, while their position is electrostatically controlled at lower frequencies to prevent them from drifting apart. In this configuration only the diagonal elements of the gravitational gradient tensor can be estimated. In this case and with the given intrinsic performance of the laser interferometer, we derive a set of requirements on the precision of the sensor parameters in order to reach a level of precision compatible with the signal of interest. Based on this analysis and considering the different sources of noise and uncertainty, we then give a first estimation of the total error budget of the derived gravitational gradients in the sensor reference frame. We discuss these results and the ability of an optical gradiometry mission to map the time-variable gravitational field with respect to the ESA’s updated Earth System Model and the science requirements from Emotion² report. Finally, we identify the main limitations of the concept and suggest possible solutions to overcome or mitigate them. In particular, the determination of the orientation of the gradiometer reference frame with respect to the Earth fixed frame with a sufficient accuracy and precision has not yet been addressed in depth.

A fundamental problem concerning the development of empirical internal magnetic field models using satellite and ground based data is the estimation of external field contributions originating from sources in the ionosphere and the magnetosphere.  Traditionally one had to limit data to geomagnetically quiet periods to minimize such contributions.  However, even during quiet times, such contributions remain significant.  Here, we show that global magnetosphere-ionosphere models, such as the OpenGGCM, can be used to estimate the external perturbations, which can then be used to correct the data.  We will show several examples for quiet, disturbed, and storm times.

The laterally heterogeneous structure of the Antarctic continental lithosphere affects the response to the time-varying cryospheric loads at the surface, and mantle dynamics at depth. So far, knowledge of these complex interactions has been quite sketchy: glacial isostatic adjustment is generally studied by means of layered rheological models, intraplate seismicity is largely unknown, uncompensated topography is not well understood, and the lithospheric structure is poorly constrained. The possibility to use new geophysical data acquired during the IPY (International Polar Year), together with those collected with the European satellite mission GOCE provides the chance to improve our understanding of the cryosphere-lithosphere interactions.

In particular, our contribution will be focused on the reconstruction of a crustal structure, discretized on 0.5° x 0.5 tiles and nine layers that represent the main geological discontinuities below the studied area. The available Global Geopontential Models (GPM), based on the GOCE mission, will be tested upon three starting crustal models: 1. the part of the global crustal model CRUST 5.1 (Bassin et al., 2000) which covers the Antarctic plate; 2. the crustal model of Baranov and Morelli (2013); 3. The crustal model of Block et al. (2009).
 

Patchy Pulsating Aurora is a common ionospheric phenomenon. The PPA patches are normally tens to hundreds kilometers in extent with luminosity that oscillates quasi-periodically. The time scale of these oscillations is typically between 5 and 40 seconds. The precipitating electrons that cause the PPA have energy that is typically in the few to 10s KeV, and the precipitation is modulated by variations in the power of the chorus and other magnetospheric plasma waves that cause the electron precipitation. The Swarm mission consists of three satellites, two of which (Swarm A and Swarm C) fly side by side separated by ~100 km in east-west direction. The instruments on each observe ionospheric processes by providing high precision data of electron temperature, electron density, and the electric and magnetic fields. For this study, conjunctions between the constellation of Swarm A & C with pulsating aurora patches observed by THEMIS All Sky Imagers are identified.  By comparing the electron temperature measurements from the two satellites, we show that the electron temperature is enhanced in the pulsating aurora patch region which may be electron heating induced by the plasma waves that cause the pulsation of pulsating aurora.  

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The following is a submission for the Fourth Swarm Science Meeting which takes place as part of ESA's Living Planet Symposium 2016. "The Fourth Science Meeting will also serve as a platform to discuss the further evolution of the mission - in relation to other ongoing initiatives and programmes - based on input from users." The poster intends to support this discussion.

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Abstract:

The three satellites of ESA's magnetic field mission Swarm were launched into a common low Earth circular orbit in November 2013. Since completion of the orbit acquisition phase in April 2014 one satellite (Swarm-B) is flying in a higher orbit with an inclination of 87.8 deg and an altitude decaying from 520 km. The other two satellites are Swarm-A (trailing) and Swarm-C (leading). They form the lower pair with an initial altitude of 473 km, an inclination of 87.4 deg and an ascending node difference of 1.4 deg.
The original mission analysis foresaw a decay of the lower pair down to 300 km altitude within 4 years after launch. The target altitude of the launcher injection orbit was selected accordingly with some margin due to uncertainties in the solar activity prediction. However the final altitude selection had to be provided more than half a year before launch. Following several launch delays, the major part of the mission falls now beyond the maximum of the current solar cycle. Because of the lower radio flux and geomagnetic activity, the air drag forces are now much lower and the actual decay takes longer.
As a first countermeasure the target for the inclination difference between Swarm-B and Swarm-A/C was reduced to 0.4 deg shortly before the start of the orbit acquisition manoeuvre sequence early 2014 such that the LTAN drift between the orbit planes of B and A/C has been reduced to 1.5 h per year to avoid too large difference towards the end of the mission.

First the poster describes the routine orbit determination approach by ESOC flight dynamics which is used to determine absolute drag scale factors. Based on the in-flight calibrated values, long term orbit predictions have been done every half a year and can be compared against the actual observed decay. This gives good confidence for the prediction of the future altitude evolution. The latest results for different confidence levels of the predicted solar activity are given.

Then estimated relative differences between the drag scale factors of the lower satellite pair are presented together with the evolution of the lower pair separation and the corresponding maintenance manoeuvres.

Finally, the major part of the poster presentation focuses on different options to change the future orbit evolution. During the initial orbit acquisition phase 40% of the fuel was consumed. Since then the yearly consumption has been less than 1% of the initial fuel and is mainly spent by the onboard attitude control. Thus a considerable amount of fuel is left which can be used to:

change the future evolution of the LTAN separation of the orbital planes between B and A/C to stay around 6 h (90 deg) for an extended time period. The most efficient way is not a direct change of the node but to influence the rate of the node rotation by a change of the orbit inclination. Different inclination change scenarios with the corresponding LTAN evolution and fuel consumption (to be split between Swarm-A and B/C) are shown.

extend or reduce the mission lifetime by raising or lowering of the orbit while it is still relatively high. At the current altitude it is still possible to influence the re-entry by several years. For example one could aim to reach the altitude of 300 km at the time of the solar cycle minimum.

perform altitude maintenance manoeuvres once a low altitude is reached.

reduce the ascending node crossing time difference between the lower pair satellites during certain time periods.

Ionosphere is a layer of the atmosphere that affects the radio signals due to its ionization level. When the ionization levels are getting higher, scillintilations occur on the radio signals and causes performance degradation of GNSS receivers. Electron density levels of ionosphere are variable with diurnal, seasonal, solar and geomagnetic activities. Ionospheric characteristics are different around the world, in order to understand the mitigation and detection of ionospheric disturbances threat models have to be established locally. Threat models are created according to statistical properties of the ionospheric gradients. An ionospheric disturbance can be modeled as a linear wave front moving with constant speed. Gradient is the slope of the linear wave and can be estimated by station-pair and time-pair methods. In the time step method, there are two satellite that are visible to same station. Ionospheric delays of same pair at one epoch are compared with the same pair at different epoch. By differential delay, gradient is computed as the division of differential delay to distance between ionospheric pierce points. This method introduces an error source which is called temporal decorrelation error. Correspondingly, the computation of the gradients are more complex than station pair method. Therefore, in this study station pair method is used in the gradient estimation process. The station-pair method treats each pair of stations as a reference station and rover receiver pair. Pairs are configured to view the same satellite. Ionospheric slant delays for each of the two stations are differenced at each epoch. Differential delays are then divided by the distance between the two stations to compute slant ionospheric gradients. Ionospheric delays can be estimated from the code and carrier pseudorange measurements of the GNSS receivers.  For continuous and robust delay measurements both code and phase measurements are used for the calculation of the ionospheric delay estimations by using IONOLAB-STEC and IONOLAB-BIAS methods. (www.ionolab.org). In this study, accurate estimates of ionospheric delays obtained by using dual-frequency GPS measurements from the stations of the Turkish National Permanent GNSS Network (TNPGN-Active). The receivers provide daily continuous raw data for the date range 2009-2012 with 30 seconds time resolution. To avoid multipath effects, 40 ̊ masking elevation angle are used in the study. According to the statistical properties of the receiver measurements, receiver network region is subdivided into 19 regions.  Within each region the stations statistical trends are similar to each other. This similarity serves a basis for the trends of each station in each region. In the detection process ionospheric delays and gradients are computed for each L1 and L2 frequencies. Gradients are analyzed yearly, monthly and daily for each region automatically according to their statistical parameters. To detect an anomaly a threshold procedure is used. The threshold values are taken as median of stations for a month plus two times maximum value for a month.  If the maximum value of the day is greater or lower than the threshold bound, the day is grouped as an anomaly day. Finally, the upper bounds for the threat model determined by processing the historical data of days that have ionospheric disturbances. One important result is reduction in the level of the gradients for the high elevations. Maximum gradients are observed as nearly 40 mm/km for the observation period over Turkey. Acknowledgments. TNPGN-Active RINEX data set is made available to IONO-LAB group for TUBITAK 109E055 project at http://www.ionolab.org/.This dataset can be accessed by the permission from TUBITAK and General Command of Mapping of Turkish Army ( http://www.hgk.msb.gov.tr/). This study is supported by the joint TUBITAK 112E568 and RFBR 13-02-91370-CTa and joint TUBITAK 114E092 and AS CR 14/001 projects.

We present an analysis of the electron temperature (Te) measured by the Swarm Langmuir Probes and their comparison with the IRI (International Reference Ionosphere) model. IRI includes two options for the electron temperature - TBT-2012 and Bil-1985 based on different sets of earlier satellite measurements. Both options are used in this study. We found that the variation patterns of Swarm-Te and IRI-Te are similar, however, they differ substantially in absolute values. The differences between Swarm-Te and IRI-Te vary with local time and latitude. The smallest differences are observed at high latitudes where Swarm-Te is higher than IRI by about 10%. The largest differences were found at low and equatorial latitudes during nighttime, where Swarm-Te is more than 100% higher than what IRI predicts. Complementary information about the electron concentration shows the opposite behavior (Swarm electron concentration is up to 60% lower at the geomagnetic equator than IRI predicts). We also present comparisons of the Swarm-Te data with quasi-simultaneous C/NOFS ion temperature (Ti) data at night and low latitudes where thermal equilibrium between electrons and ions can be assumed (Te=Ti). This comparison confirms that the Swarm-Te is about 100% higher than corresponding C/NOFS-Ti data. We will try to introduce a correction procedure for the Swarm-Te data to obtain a better agreement with IRI.

The gravity gradient data collected during the GOCE mission are extraordinary valuable, because they allow a stand-alone reconstruct of a high resolution gravity field model only by GOCE data, which are well defined and homogeneous. But these data have to be handled carefully, because the noise structure of the gradiometer and star sensor measurements causes high correlations in the gravity gradient measurements. Especially during the GOCE low orbit operation campaign (LOOC) changing correlations and outliers has to be taken into account because of the harsh environment in such a low orbit.

By a robust residual analysis especially large and rapid changes in the stochastic behaviour can be located and these conspicuous data sequences can be identified. For the further processing two questions arise immediately: 'Are these conspicuous data outliers or do they reflect an additional signal?' and 'How should we treat these data?'. At first glance it seams to be uncritically to neglect these data because of the highly overdetermined system. But a short look on the regional distribution of these conspicuous data unsettle this decision because of the regional accumulation of these data. Due to the harsh environment in the low orbit also the stationary of the measurement noise has to be scrutinized and a possible benefit of a time variable treatment of the correlations has to be investigated.

In the past the non-stationarity of the signal was taken into account in the GOCE-TIM models by individual (stationary) filters for the different data segments (for the whole mission around 90 segments are identified mainly caused by data gaps, calibration phases and manoeuvres). In this presentation we want to discuss the possible benefit of modelling the correlations by non-stationary stochastic processes with the aim to construct time variable decorrelation procedures to improve the stochastic model. On the one hand side to describe the conspicuous sequences in an appropriate form and on the other hand to allow for a continuous (small?) transition of the stochastic behaviour in time. As a main strategy we want to include almost all data into the model and use a complex stochastic model to represent the behaviour of the data.

As an appropriate mathematical description of these non-stationary stochastic processes we use an autoregressive representation with time variable coefficients. The time variability of the coefficients are parametrized by a B-spline representation in time. This representation allows a flexible description because both the choice of the intervals and the smoothness of the transition can be modelled data adaptive.

To study the impact of these time-variable representation of the stochastic process we perform a full gravity field reconstruction computed with the time-wise approach. Some special GOCE data sequences are selected and the results from the standard approach, which is used in the TIM5 model, are compared with this time-variable approach. As a third model we have also a look to the results of a robust approach, where all these conspicuous data sequences are treated as outliers and neglected during the computation.

The equatorial electrojet (EEJ) current system and the eastward electric
field which drives it, influence much of the ionospheric electrodynamics
at low-latitudes. The Swarm Level-2 operational equatorial electric field
(EEF) chain produces estimates of the EEF and equatorial electrojet (EEJ)
current flow for each dayside orbit for all three satellites. The EEJ
currents are derived from the absolute scalar magnetometer (ASM) data only.
In this talk, we will investigate improvements to the equivalent line
currents when using the full vector measurements. With the updated
current profiles, we will investigate the seasonal, local-time,
longitudinal and lunar dependence of the EEJ current system, and present
a quiet-time climatological model of the EEJ current.

The Mean Dynamic Topography (MDT), defined as the sea level above the geoid, represents the signal of interest for many oceanographic circulation applications and can be simply computed as the filtered difference between a given Mean Sea Surface (MSS) and the geoid. Nevertheless, its computation in the Mediterranean Sea, where the circulation is characterized by small details and sharp coastal gradients, still remains a critical issue mainly due to the lack of a sufficient accurate and high-resolution geoid.

The improvement given by GOCE in the knowledge of the geoid up to few centimeters at a resolution of about 100 km has been already demonstrated. This geoid has been used to improve the MDT estimate for open oceans, but its capability to get the major circulation patterns in semi-enclosed basin is still an open issue, although in the Mediterranean Sea some promising results have been already achieved, for example within the ESA STSE MEGG-C project.

In this work a GOCE-only MDT for the Mediterranean Sea has been computed using the CNES-CLS2011 MSS and one of the latest releases of the GOCE global gravity models (i.e. GOCE TIM R5). To this aim a standard collocation approach, adapting the MDT signal and error covariance functions to the local characteristics of this semi-enclosed basin, has been applied in order to get an optimal regional solution. The goal is not to estimate the best Mediterranean MDT, which inevitably requires to use other data sources like for example marine gravity and drifter observations, but to derive a solution that depending only on the GOCE geoid emphasizes the real contribution of this mission to the Mediterranean Sea stationary circulation. In particular in order to evaluate the actual GOCE contribution, a numerical assessment of the obtained circulation model has been performed by comparing the GOCE-only MDT with independent data; moreover some statistical tests have been defined to identify the circulation patterns that are visible by GOCE. This assessment is possible thanks to the availability of the MDT error covariance information. From preliminary studies based on a global Wiener filtered MDT developed in the framework of the MEGG-C project, it comes out that GOCE has a positive impact in the Mediterranean Sea circulation.

We present a comprehensive study of multi-wavelength auroral emissions, specifically that of green-line and red-line aurora.  Auroral arcs and pulsating aurora have been extensively studied using the THEMIS white light all-sky imaging array (assumed to be measuring predominantly green-line emissions during these types of events).  The newly deployed Redline Emission Ground-based Observatory (REGO) all-sky imaging array provides the first large-scale observations of the elusive 630.1 nm redline aurora.  In this study we look at a subset of redline emission aurora and examine their morphology and electromagnetic properties using the Swarm constellation of satellites.  The Swarm satellites provide a unique view of these phenomena, enabling multi-point observations of the electric and magnetic properties of the low energy component of the aurora.  In particular, we use in situ observations of field-aligned current derived from magnetometers on board swarm to determine if current magnitudes play a role in redline auroral luminosity (calibrated to Rayleighs) and orientation.  In addition, we explore the relationship between the auroral morphology of multiple auroral emission wavelengths and their relationship to geomagnetic activity levels and Poynting flux.

In 2009 GOCE satellite gravity mission was launched to measure gravity gradient with high spatial resolution and of high accurcy. It can give better understanding and modelling of earth's Interior and its dynamic process. Its data can be combined with other gravity data like Grace and terrestrial gravity data. Gravity gradient shows sensitiveness with earth's density structure and upper crust. It provides geological features' (like faults, lineaments and large instructions) edges in better resolution form.

I have taken satellite gravity data to prepare homogeneous gravity model for lithosheric modelling. To increase accuracy we can use combined model of satellite and land measured gravity data or two satellite data. By calculating tectonic subsidence and heat tectonic flow according to muturity we can define area of hydrocarbon exploration.

We utilize conventional tracking data to extend the record of polar ice sheet melt obtained by the Gravity Recovery And Climate Experiment (GRACE) mission. While the GRACE-based estimates only start in 2002, our reconstructed fields add at least a decade of coverage to the existing GRACE-based time series of polar ice sheet mass changes. The three different conventional tracking data fields consist of satellite laser ranging (SLR) measurements and one field also uses Doppler tracking (DORIS) measurements. For each solution, we reconstruct a single set of monthly, global gravity fields that has been augmented by GRACE. To do so, we combine these conventional tracking data and GRACE fields via an Empirical Orthogonal Function (EOF) analysis, whereby the conventional tracking data temporal modes are obtained by fitting the SLR Stokes coefficients to the GRACE spatial modes via linear least-squares adjustment. Combining those temporal modes with GRACE spatial modes yields the reconstructed global gravity fields. These reconstructed fields contain errors that are inherent to the models, the method, and the data. To assess the errors from the data, we compare the three reconstructions that are based on the three different SLR-based fields. First, we use the solution from the Goddard Space Flight Center (GSFC, Dr. Frank Lemoine), which utilizes GEODYN software and includes DORIS measurements. Second, we plan on using the solution from the Deutsches Geodaesie Forschungsinstitut (DGFI, Dr. Mathis Bloßfeld). Third, we plan on including the solution from the Astronomisches Institut Universität Bern (AIUB, Prof. Adrian Jäggi), which employs the Bernese software. Specifically, to determine the errors from these SLR-based data, we examine the propagated covariances and their influence on the melt estimates. Furthermore, we investigate the validity and consistency of the interannual behavior of each reconstructed melt estimates against estimates from GRACE and from independent Mass Balance methods. Moreover, we assess how various processing strategies from each research center (GSFC, DGFI, and AIUB) affect the reconstructed estimates. Finally, we determine a set of error bars to these reconstructions.

The three Swarm satellites carry Langmuir probes, LPs, which are part
of the electric field instrument, EFI. From the LP data the electron
density and temperature are estimated, with a spatial resolution of a
about 3.6 km. They are now available nearly continuously since the
launch in November 2013. The globally outstanding feature of the
density derived from Swarm is, as already seen by several earlier
missions, the equatorial anomaly developing during the day and
decaying after sunset. At Swarm altitudes, between about 450 and 510
km, the anomaly has the form of a double band of density maxima
roughly 10 degrees north and south of the magnetic equator. Mainly
after sunset density gradients are seen at the edges of plasma
bubbles. The density variations are relatively stronger at the equator
between the density maxima, but absolutely the variations are highest
in the double band. The on-board GPS is mainly affected near the
maximum of the background density and mostly when density gradients
are seen by the LPs. The geographic distribution of the on-board GPS
disturbances seems to be similar as seen on the ground, however, the
signal phase rather than the amplitude is disturbed. The proximity of
the receiver to the causing density variations could be an explanation
for this.

The LP controls also the bias of a faceplate masking the entrance of
ions into the EFI, and measures the current at a high resolution
corresponding to length scales of about 500 m. Plasma irregularities near
the equator are expected to be oriented according to the magnetic
field direction. Swarm orbits near the equator at angles parallel and
nearly parallel to the magnetic field and we show power spectra of
density variaiotns and their indices in these directions.

Observation and analysis of the ionospheric irregularities at the high latitudes using GPS measurements represent a very actual task for both scientific point of view and Global Navigation Satellite Systems (GNSS) applications. For representation of the high-latitude irregularities spatial evolutions and estimation of their linkage with the Earth’s magnetosphere we construct and analyze the maps of the GPS-based index: Rate of TEC index (ROTI). The ROTI maps allow us to estimate the overall fluctuation activity and auroral oval evolutions, in general, the ROTI values correspond to the probability of the GPS signals phase fluctuations. The Southern Pole is the region where a dense network of permanent GNSS stations is not established yet and existing ground-based datasets do not allow to estimate development of the ionospheric irregularities over the Southern polar region.  We present results of the implementation of the ROTI mapping approach to the space-borne GPS data from the three Swarm, GRACE and TerraSAR-X satellites to study the auroral irregularities simultaneously over the Northern and Southern polar regions and discuss the obtained features comparing with ground-based and in situ measurements.

In gravity field studies satellite-only models and terrestrial data may successfully complement each other. Potential theory forms the respective basis, but the problem considered is overdetermined by nature. In this paper, therefore, methods for solving boundary-value problems are used together with optimization concepts. The compatibility of the two data sources is examined and the representation of the optimized solution is investigated. In the first stage the solution is expressed by series of spherical harmonics and their summation is approached by numerical techniques directly. Subsequently, mathematical analysis aspects are given more attention. Properties of the series are discussed with the aim to find a way for their closed form representation. This results in the respective integral kernels (Green’s functions) for the problem discussed. The integral representation of the solution gives a better insight into the role, which the input data have in the global and the local modelling of the gravity field. Thus it also illustrates more clearly the contribution of the terrestrial data to the optimized solution. Numerical examples and real case studies are added. Terrestrial data and GOCE based models are used for this purpose.

Satellite gravity anomalies and gradients in marine environments have been commonly studied for a spatial description of tectonic features (trenches, ridges, oceanic and continental lithospheric boundaries, etc), crustal and lithospheric configuration and elastic properties, or to study the gravity signature of a mega-earthquake, but gave minimal attention to the temporal variability of these anomalies and gradients. 

Vertical gravity gradients (T_zz) have been commonly used for delineating the location of superficial anomalous masses, with better detail and accuracy than the gravity anomaly itself. Using the monthly solutions of GOCO05s, from November 2009 to October 2013,  we are in the process of identifiying a link between vertical gravity gradients and sea bed density anomalies (specially great mass movements) associated with sedimentation, erosion and volcanic processes  in the Intra-America seas, given the great variety of sea bed morphodynamic environments in this part of the world.

Even though this research is ongoing, we aim to identify the gravity gradient signature of geomorphic features such as Mississipi and Magdalena fans, and to better understand the sedimentary processes derived from Orinoco and Amazon supply rates, that configure the morphology of the southern Lesser Antilles region. We also want to test the ability of the GOCO gravity gradients to detect other signals related to active thermal processes in the oceans like volcanism and diapirism.

Equatorial ElectroJet (EEJ) is an intense eastward electric current circulating in the ionospheric magnetic equator band between 100 and 130 km of altitude in E region. In this paper, we present a study of the equatorial electrojet (EEJ) phenomenon by data of ground magnetic observations of African region. Recorded ground data is provided by IPGP (Institut de Physique du Globe de Paris (Français)) covering region situated in the African equatorial sector [Bakarywere (BAK), Samogossoni (SAM) and Korhogo (KOR)]. In addition, the satellite data used in this study are obtained with SWARM satellite vector magnetometer data respecting magnetically quiet days with Kp<2.

In this paper, we process to separate and extract the electrojet intensity signal from other recorded signal-sources interfering with the main signal and reduce considerably the signal to noise ratio during the SWARM recording phase and ground measurements. This pre-processing step allows removing all external contributions in regard to EEJ intensity value. EEJ current intensity is then extracted and examined the effects of the seasonal variation, daily variations of the horizontal and vertical components (H, Z), also we studied the local time and longitudinal dependence of EEJ. In order to enhance the quality of the magnetic signature of EEJ separated and increase signal to noise ratio influenced by the other source, we compare both ground magnetic measurements and SWARM satellite data in term of correlation.

This presentation will describe the latest update of the scientific geomagnetic field model Pomme (http://geomag.org/models/index.html), which includes main, crustal and external contributions. Furthermore, with two and a half years of measurements available, one can now begin to accurately resolve secular acceleration from Swarm data alone.      

The Earth's gravity acceleration is the dominant force which governs the satellite's orbital motion. The better the knowledge on the geopotential the more accurate the orbit is. Launching the gravity field dedicated missions, i.e.,  GRACE, has improved our knowledge and led to better dynamic orbits. In this article, we investigate the  GRACE models' contribution to Envisat satellite orbit and consequently on the accuracy of the products. A rich data set of altimeter crossovers and tracking observations from SLR (Satellite Laser Ranging) and PRARE stations has become available, enabling significant reduction of ENVISAT radial orbit error and thus improving the signal to noise ratio of many phenomena in the above mentioned research areas. This data has been used to develop an improved gravity field model for the ENVISAT satellites. Moreover, we analyze the effect of this improvement on the relative accuracy of the multi-satellite SAR mission from orbital geometry point of view. 

The most recent advances in the geoid determination, provided by the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) mission, together with the continuous monitoring of the sea surface height by the altimeters on board of satellites have made possible to obtain ocean geostrophy combining altimetry, GOCE and ArgoData. 
A new estimate of the North Atlantic geostrophic circulation from the surface down to 1500 m depth has been computed for the 2004-2014 period using an observation-based approach that combines altimetry with temperature and salinity through the thermal wind equation gridded at one degree longitude and latitude resolution. The geostrophic circulation was validated in the North Atlantic Ocean against in-situ observations.

In this work we study  the Mediterranean Sea Circulation observed from Mediterranean absolute surface geostrophic currents(SGC) using satellite data only. Nowadays it is possible to combine more than 21 years of altimetry data with a geoid model based on GOCE data to obtain the dynamic topography with an unprecedented precision and accuracy. In addition, the improved accuracy in satellite altimetry data has allowed us to determine ASL maps at weekly resolution.

 Mediterranean Sea’s circulation climatology and variability of the SGC is estimated for the period spanning 1993–2014, from weekly SGC maps gridded at one eighth degree longitude and latitude resolution resolving spatial scales as short as 70 km. For presentation, this data set is averaged monthly and the results are interpreted and validated with simulations from Mercator models.