Land and Cryosphere Future Missions

GeoSTARe is a Synthetic Aperture Radar concept placed in geosynchronous orbit and providing, for 80% of the time, a continuum of images where space resolution can be traded for image time.

The concept under study is a dual-beam-dual-frequency payload, where a common reflector is illuminated both both a L band, dual polarized feeder and an X band one, resulting in respectively in a WIDE and a SPOT beamwidth. The L band wide beam provides sub-continental coverage at coarse resolution, whereby X band provides fine resolution, high sensitivity to slight deformations and surface roughness. A C band system is also studied as backup solution providing a costeffective solution with more mature components and complementarity to Copernicus S1, but with some impact of applications.

The geostationary orbit will enable at one time the hosting of the payload on a telecommunication system and immediate data downloading for exploitation. It ensures access  over more than one continent, like Europe and Africa, limited in latitude by the incidence up to 60° north and south. Furthermore, the view point is fixed, although complementary with LEO-SAR (South-North), and wouldn’t image fast moving targets, like sea surface.

Nonetheless, not only will GeoSTARe be unique technically, as the first radar in geosynchronous orbit, but scientifically it will enable a variety of observations to be made that otherwise cannot be addressed. To do so we will need to achieve two main scientific objectives:

1. To generate a guaranteed sub-daily series of radar observations to measure rapidly developing surface events such as river floods, landslides, earthquake damage and lava flows.

2. To exploit the trade-off given by variable radar return signal integration times in various retrievals of water such as field-scale soil moisture and km-scale water vapour as an input to NWP.

The system will be able to generate Radar backscatter maps, interferometric surveys, with short interval (starting from 15’) but 12 hours revisit, and possibly tomographic stacks.

Last, but not least, it can evolve into a MIMO swarm where performances in terms of revisit and image quality scale roughly with the square of the number of cooperative sensors.

Some of the potentials will be discussed in the paper

Knowledge of properties of terrestrial snow, such as the extent and duration of snow cover, as well as snow mass or SWE (Snow Water Equivalent), are required for monitoring and modelling e.g. the water and energy balance of the surface of the Earth, as well as for many applications in hydrology. The scarcity of observation networks makes data collected in situ unreliable for arctic and boreal areas, while state-of-the-art methods for retrieving SWE from Earth observing satellites rely on passive microwave sensors [1]. Although these provide good global coverage and a long history of observations, the accuracy is limited due to the inherent coarse spatial resolution of the sensors and saturation of the signal for high values of SWE. Specifically, there is a clear need for timely, regular observations of global snow mass at an intermediate (500 m to 1 km) spatial resolution with 1-2 day revisit time. CoReH2O (Cold Regions Hydrology High-resolution Observatory), a candidate for ESA’s 7^th Earth Explorer [2], aimed to address some of these issues by providing information on SWE, as well as snow accumulation over glaciers, at a resolution ranging from 200 to 500 meters and a revisit time between 3 and 15 days. The sensor envisaged for CoReH2O was a dual polarization, dual frequency Synthetic Aperture Radar (SAR).

With the non-selection of CoReH2O, the snow science community has been investigating alternate options for global snow mass retrieval. Dedicated mission concept studies have been launched both within Europe and internationally e.g. at NASA Goddard Space Flight Centre, the Jet Propulsion Laboratory (JPL) and the Canadian Space Agency (CSA). At NASA, a dedicated multi-sensor campaign focused on snow cover are planned to address existing observational gaps. In this presentation, we provide the scientific justification for improved snow mass retrieval, compared to capabilities of present Earth Observing systems. We outline the main investigated mission concepts and sensor options which have the potential to address this urgent need. The investigated concepts include both active and passive microwave options. The drawbacks and benefits of the alternate concepts are discussed in terms of spatial and temporal coverage, spatial resolutions, technological maturity, scientific maturity (retrieval skill) as well as the potential of different concepts for retrieving secondary geophysical parameters, such as sea ice characteristics.

[1] Takala M., K. Luojus, J. Pulliainen, C. Derksen, J. Lemmetyinen, J-P. Kärnä, J. Koskinen, and B. Bojkov, 2011. Estimating northern hemisphere snow water equivalent for climate research through assimilation of space-borne radiometer data and ground-based measurements. Remote Sens. Environ., 115(12): 3517-3529.

[2] Rott, H., S.H. Yueh, D.W. Cline, C. Duguay, R. Essery et al., 2010. Cold Regions Hydrology High-resolution Observatory for Snow and Cold Land Processes. Proc. IEEE, 98(5): 752-765.

A reliable quantitative spatial assessment of crop parameters, such as LAI, biomass accumulation, nutrition status etc., is a prerequisite for optimized agricultural management. Remote sensing, due to its inherent spatial character, provides a perfect method for retrieving this kind of information.

Remote sensing of vegetation, however, is difficult due to the complex and not always unique interrelation between crop status and spectral signature. In addition, vegetation is a spatially heterogeneous and dynamically evolving land surface category, so that not only the spectral capabilities but also the spatial and temporal configurations of sensor systems determine the potential for the retrieval of vegetation parameters.

The launch of Sentinel-2 is considered a milestone for vegetation studies using optical remote sensing due to its high data quality, its high spatial resolution of up to 10m and – above all – due to its high revisit rate of five days (Sentinel-2A in combination with Sentinel-2B). This setting makes it possible to trace the dynamic development of agricultural crops during their growth cycle. Nonetheless, the operational character of the Sentinel-2 mission comes at the expense of a multispectral configuration instead of a contiguous spectral coverage.

Quite in contrast, the future German Hyperspectral Satellite Mission EnMAP (Environmental Mapping and Analysis Program) will provide full VNIR-SWIR spectral coverage with 249 narrow spectral bands and a high signal to noise ratio. EnMAP will provide data at 30m spatial resolution which is considered to be adequate for agricultural applications. However, due to the scientific character of the mission, no high revisit rates can be expected from EnMAP, making the mapping of seasonal vegetation growth and development a challenge yet to overcome.

This study therefore aims at assessing the differences and possible synergies between both missions with respect to the retrieval of crop parameters. For this purpose, results from an exhaustive field campaign conducted on Winter Wheat during the growing seasons of 2014 and 2015 in the vicinity of Munich, Southern Germany, are used. During the campaigns, a selection of bio-chemical and plant-physiological parameters like LAI, leaf pigment concentration, canopy architecture, dry matter and water content were measured in-situ at nearly weekly intervals. Since neither Sentinel-2 nor EnMAP were in operation during these campaigns, satellite data is simulated for a 30 x 30m plot – one EnMAP pixel or nine Sentinel-2 pixels respectively – based on about 1000 field spectroscopy measurements that were taken simultaneously to the parameter sampling. For this purpose, specific end-to-end simulators for Sentinel-2 (SeteS) and EnMAP (EeteS), developed at the GFZ German Research Centre for Geosciences in Potsdam, are applied which take the respective spatial, spectral and radiometric sensor properties as well as atmospheric influences into account.

Based on the resulting time series of simulated satellite data and the accompanying in-situ measurements, the capabilities of both sensors for the retrieval of vegetation parameters are compared. Since the study is based on simulated satellite data, the temporal frequency of observations is not limited by the actual capacities of the satellite systems. The results of the study thus also allow a glimpse into a possible future, where hyperspectral observations might operationally become available.

Understanding the behavior of polar ice sheets and predicting future changes in their volume and mass are critical to improve understanding of weather, climate, and the water cycle on Earth. Because of the extreme environmental conditions associated with polar ice sheets, satellite sensors are the most suitable tools for observing geophysical quantities characterizing  ice sheets and for the monitoring their temporal and spatial variations. Currently many of these quantities such as ice sheet surface topography, ice surface velocity, mass change, ice sheet thickness, surface accumulation rate, internal stratigraphy and basal geology can be retrieved, with an acceptable accuracy, from data acquired by airborne and spaceborne remote sensing instruments. Internal ice sheet temperature is absent from this list although it is a primary factor in determining internal deformation and ice flow, and thus is crucial for better understanding polar ice sheet dynamics.

Recent activities have demonstrated that microwave radiometry offers the potential to remotely sense internal ice sheet temperatures. In particular theoretical results, were obtained using an e.m. model (the DMRT –ML),  suggest that microwave radiometry at frequencies ~0.5 - ~ 2 GHz can probe sub-surface ice sheet emissions at depths up to a few km. Results indicate that brightness temperatures of ice sheets significantly change with frequency : higher brightness temperatures at lower frequencies show that at these frequencies deeper ice layers start to contribute to the overall thermal emission of ice sheets. At higher frequency bands on the other hand, their effects diminish and the resulting brightness temperature is lower.

This is similar in concept to atmospheric temperature profiling, in which multi-frequency measurements of brightness temperatures near an atmospheric gas absorption resonance are used to sense temperatures at altitudes that vary with distance in frequency from the absorption line. While sensing ice-sheet temperatures is complicated by the absence of a strong absorption resonance as well as the presence on inhomogeneities, the clear potential for obtaining temperature information at varying depths through multi-frequency measurements motivates the analyses performed.

To test this novel concept for cryospheric studies, the Ultra-Wideband Software-Defined Radiometer (UWBRAD) has been developed under the support of the NASA Instrument Incubator Program (IIP). The instrument will provide measurements of ice sheet thermal emission in 12 frequency channels over the range 0.5-2 GHz. The instrument and the retrieval approaches will be fully tested during an airborne campaign planned in Greenland for Spring 2016. Along with the instrument development, an important part of the study was devoted to the direct modelling of the brightness temperature of the polar ice caps with coherent and incoherent models, and to the development of retrieval algorithms for estimating the vertical distribution of the ice temperature.

In order to ground test the instrument concept and  retrieval approach, a prototype version of the radiometer having four channels at 540, 900, 1380, and 1740 MHz  has been developed. This UWBRAD prototype is being deployed in a pilot experiment at Dome-C in the East Antarctic Plateau (where the Italian-French Concordia base is located) in Austral summer 2015-2016. The instrument is being deployed on the Dome-C observation  tower at a height of ~12 m,  and will collect data on a pristine area of ice sheet at incident angles of 30 and 45 deg. Clear sky observations are also planned for calibration purposes.  The data collected by the prototype will also be compared to L-band (1413 MHz) brightness temperatures measured by the RADOMEX system operating from the same tower; the RADOMEX system has been operated from the tower in multiple measurements since December 2013 for calibrating and validating SMOS data.

The presentation will provide detailed information on the mission status, in particular on the deployed instruments and their performances, on the advanced forward models and the retrieval algorithms along with the first ultra-wideband microwave measurements which will be collected in Antarctica.

UrtheCast, a Canadian company which acquired Deimos Imaging (Spain) in 2015, is currently developing the world’s first fully-integrated, multispectral optical and Synthetic Aperture Radar (SAR) commercial constellation of Earth Observation satellites (the “UrtheCast Constellation”), to be deployed over multiple launches expected in 2019 and 2020.
The UrtheCast Constellation is expected to comprise a minimum of 16 satellites (8 optical and 8 SAR) flying in two orbital planes, with each plane consisting of four satellite pairs, equally-spaced around the orbit plane. Each pair of satellites will consist of a dual-mode, high-resolution optical satellite (video and pushbroom) and a dual-band high-resolution SAR satellite (X-band and L-band) flying in tandem.
The UrtheCast Constellation will provide unmatched space-imaging capabilities, including high collection capacity, optical and SAR data fusion, weather-independent high-resolution imaging using the SAR, target revisit, and imaging latency. By flying the satellites in tightly-paired SAR and optical tandem formations, the UrtheCast Constellation is expected to offer a number of innovative capabilities, including onboard real-time processing, cross-cueing between the satellites, and real-time cloud imaging on the leading SAR satellites that enables cloud avoidance in the trailing optical satellites. By employing two orbital planes, the UrtheCast Constellation will allow for maximum revisit rates in the mid-latitudes, while providing global coverage extending to the poles.
This presentation describes the details of the UrtheCast Constellation, its development status, and the vision to integrate this capability in the European Copernicus Programme.