Introduction to the Sentinel-2 radiometric calibration activities during commissioning phase

In partnership with the European Commission and in the frame of the Copernicus program, the European Space Agency (ESA) is developing the Sentinel-2 optical imaging mission devoted to the operational monitoring of land and coastal areas. The Sentinel-2 mission is based on a satellites constellation deployed in polar sun-synchronous orbit. Sentinel-2 will offer a unique combination of global coverage with a wide field of view (290km), a high revisit (5 days with two satellites), a high spatial resolution (10m, 20m and 60m) and multi-spectral imagery (13 spectral bands in visible and shortwave infra-red domains). The first satellite is planned to be launched in mid-2015. In this context, the Centre National d’Etudes Spatiales (CNES) supports ESA to insure the calibration/validation commissioning phase during the first six months in flight. This paper provides first an overview of the Sentinel-2 system and a description of the products delivered by the ground segment associated to the main radiometric specifications to achieve. Then the paper will focus on the description of the Sentinel-2 Technical Expertise Center which is in charge of the radiometric and geometric activities during the commissioning phases of the Sentinel-2 satellites. The paper will finally address the radiometric methods and calibration sites used in this CNES image quality center to reach the specifications of the sensors, in term of absolute calibration, pixel to pixel relative sensitivity, MTF estimation and level 2 products accuracy.