Sentinel 3

The OLCI instrument, an imaging spectrometer in the continuity of the ENVISAT/MERIS instrument with numerous improvements, is embarked on-board Sentinel-3, planned for launch on December the 10^th, 2015. The instrument is designed to incorporate extremely sensitive and stable radiometry, dedicated on-board calibration and a large number of spectral channels.

The OLCI radiometric calibration, as for MERIS, is based on in-flight measurements of sun-lit diffusers. Calibration relies on the diffusers on-ground characterisation, acting as on-board secondary reflectance standards: known diffuser BRDF and viewing/illumination geometry during acquisitions allow predicting spectral radiance at instrument entrance and, together with measured numerical counts appropriately corrected from instrumental effects, deriving radiometric calibration coefficients.

Data and methodology to obtain Radiometric Calibration Coefficients and monitor their stability will be presented. The results from the first months of in-flight calibration of the instrument will be presented and discussed.

The Copernicus Programme, being Europe’s Earth Observation and Monitoring Programme led by the European Union, aims to provide, on a sustainable basis, reliable and timely services related to environmental and security issues. The Sentinel-3 mission forms part of the Copernicus Space Component. Its main objectives, building on the heritage and experience of the European Space Agency’s (ESA) ERS, ENVISAT and CryoSat2 missions.  The main objectives of the Sentinel-3 Mission are to provide a sustained operational capability to measure surface temperature, surface topography, ocean- and land surface colour/reflectance and provide products with excellent accuracy and reliability in support of Copernicus services. Services include the Copernicus Marine Environmental Monitoring Service (CMEMS), the Copernicus Global Land Service (CGLS), the Copernicus Atmospheric Monitoring Service  (CAMS), Emergency Management Service and Climate Service (3CS). Sentinel-3 will serve this broad scope of application areas using a unique suite of instruments and data products to allow European environmental policies to be administered with confidence. Developed by ESA, the overall systems architect and technical coordinator of the Copernicus Space Component, Sentinel-3 is a “workhorse” mission providing information for all Copernicus operational services. Carrying a medium-resolution (300m) multi-spectral visible imager, a precision multi-view, multi-channel infrared radiometer and a powerful synthetic-aperture radar altimeter, Sentinel-3 will be in service delivering qualified data products within 3 hours of sensing 24/7, 360 days a year. The series of Sentinel-3 satellites will ensure global, frequent and near-real time ocean, ice and land monitoring, with the provision of observation data in a routine, long-term (up to 20 years of operations) and continuous fashion, with a consistent quality and a high level of reliability and availability.

The Sentinel-3 missions will be jointly operated by ESA and EUMETSAT. ESA will be responsible for the operations, maintenance and evolution of the Sentinel-3 ground segment on land related products and EUMETSAT for the marine products. All facilities supporting the Sentinel-3 operations are in place:

The data acquisition and near real time (NRT) product generation, including data downlink and processing (NRT and offline) will be performed at Svalbard station,

ESA’s Processing and Archiving Centres (PAC), which will perform the Sentinels’ systematic non-time-critical data processing, the on-the-fly data processing for specific cases and the reprocessing in case of processing algorithms or calibration parameters upgrades:

OLCI processing and archiving will be performed at DLR,

SRAL processing and archiving will be performed at CLS,

SLSTR and Sentinel-3 synergy products processing and archiving will be performed by ACRI,

EUMETSAT’s marine centre which will perform the Sentinel-3 systematic NRT and off-line data processing as well as reprocessing of the marine data and products.  In addition, EUMETSAT’ Flight Operations Segment will take care of the routine operations during phase E2.

The Missions Performance Centre (MPC) which comprises the Operational Quality Control, the Expert Support Laboratories (ESL) and Calibration and Validation activities.

Then Sentinels’ POD Service, which generates the orbit products for the Sentinels-1, -2 and -3 missions and performs the performance monitoring of the GNSS sensors.

The ESA Post Launch Support Office taking care of the in-orbit performance monitoring of the platform and payload of Sentinel-3.

The Sentinel-3 ground segment systematically acquires, processes and distributes a set of pre-defined core data products to the users. For a detailed description of the core data products please see https://earth.esa.int/web/sentinel/missions/sentinel-3/data-products. On request from the European Commission ESA and EUMETSAT are presently assessing the possibility to include further core data products, in particular on aerosol optical depth, fire monitoring and synergistic products over land.

This paper will provide an update on the status of the ground segment operations for the Sentinel-3 mission after launch and commissioning phase, including an outlook for the data provision in the mission’s ramp-up phase.

The Sentinel-3 Mission (S-3) is part of the Global Monitoring for Environment and Security (GMES/Copernicus) European initiative. For oceanic applications, the S-3 mission will deliver continuity to existing ones ESAs ERS, Envisat and CryoSat missions. The S-3 mission will provide ocean/land colour data, sea/land surface temperature estimates and sea surface and land ice topography at least at the level of corresponding Envisat instruments, the Medium Resolution Imaging Spectrometer (MERIS) and the Advanced Along-Track Scanning Radiometer (AATSR) and the Envisat Radar Altimeter (RA). The topography payload consists in a Doppler altimeter SRAL, a microwave radiometer MWR, and 3 instruments for precise orbit computation purposes (GNSS, DORIS and laser reflector). The Sentinel-3 satellites (A and B) will fly on a new orbit with a 27-days cycle.

The SRAL instrument is a nadir Ku/C altimeter, with two operating modes: the low resolution mode (LRM), used on all past oceanographic missions and the high resolution mode (SAR) used for the first time on CryoSat. The SAR (also called Doppler) mode provides a better along track resolution (around 300m) with respect to the LRM mode.

The Sentinel-3A satellite shall be launched in December 2015, and CNES (with the support of CLS) provides a strong support to ESTEC project for the topography calibration and validation during the commissioning phase.

In this paper, we will present a full assessment of the SRAL instrument performances, both in LRM and SAR modes. The main results obtained during the commissioning phase will be discussed going through the analysis of calibrations (CAL1, CAL2), the tracking modes performances, range and SWH measurements performances and accuracy. 

The instrument and mission teams have prepared a detailed plan for evaluating and optimizing the in-orbit performance of the Sea and Land Surface Temperature Radiometer. Level-0 and level-1 data products will be used to characterize the performance of the signal channel noise, dynamic range, and calibration; scan mechanism performance, instrument thermometry, blackbodies and visible calibration system at the start of the mission.  Importantly the results will be compared against the pre-flight calibration data to determine any changes from ground-to-orbit.

 In this paper the authors present the available results of the early in-orbit characterization of the instrument performance and the impact on the calibration.

The Sentinel-3 Mission Performance Centre provides an environment to perform the calibration and validation of the Sea and Land Surface Temperature Radiometer data. In this paper the authors present the initial results of the evaluation of the first SLSTR level-1 and 2 products generated during the early mission phase.

Comparisons against in-situ buoy measurements; ship borne radiometers and other satellite datasets will give an early evaluation of the accuracy of the SST and LST measurements.

The validation work will also investigate the response of the SLSTR channels over active fires, gas flares and volcanoes