干旱区生态环境知识资源中心

The recently launched SENTINEL-3A (S3A) satellite measures sea surface topography, sea/land surface temperature, and ocean/land surface colour with high accuracy as part of the Sentinel 3 mission. The mission provides data continuity with the ENVISAT mission through acquisitions over a long duration making use of four identical satellites each equipped with multiple sensing instruments. Two of them, OLCI (Ocean and Land Colour Imager) and SLSTR (Sea and Land Surface Temperature Radiometer) are optical sensors designed to provide continuity with Envisat's MERIS and AATSR instruments. During the S3A commissioning phase, in-orbit calibration and validation activities are conducted. Instruments are in-flight calibrated and characterized primarily using on-board devices which include diffusers for the reflective and black bodies for the thermal spectral channels. Vicarious calibration methods are used in order to validate the OLCI and SLSTR radiometry for the reflective bands. These methods make use of earth observation data over dedicated natural targets such as Rayleigh scattering, sunglint, desert sites, Antarctica, and tentatively deep convective clouds. Tools have been developed and/or adapted (S3ETRAC, MUSCLE) to extract and process Sentinel-3 data. Based on these matchups, it is possible to provide an accurate checking of many radiometric aspects such as the absolute and interband calibrations, the trending correction, the calibration consistency within the field-of-view, and more generally it provides an evaluation of the radiometric consistency for various type of targets. Another important aspect is the check of cross-calibration between many other instruments such as MERIS and AATSR (consistency between ENVISAT and Sentinel-3), MODIS (consistency with the GSICS radiometric standard), as well as Sentinel-2 (consistency between Sentinel missions). The early results, based on the available OLCI and SLSTR data, are presented and discussed.