Sentinel-1A Calibration Support during Routine Operation

Inhalt:
Sentinel-1A (S-1A) is the first of two satellites for global Earth monitoring in C-band in the frame of the COPERNICUS program of the European Commission and the European Space Agency (ESA). After launch in April 2014, the calibration of the SAR instrument was performed by ESA and their partners during the commissioning phase. Additionally an independent verification of the Sentinel-1A instrument calibration was undertaken by the German Aerospace Center (DLR) on behalf of ESA. However, as the commissioning phase was executed under non-ideal conditions the strong requirement for the absolute radiometric accuracy of 1 dB (3sigma) could not be achieved. In order to improve the radiometric and polarimetric performance of S-1A, further support has been given by the DLR for additional calibration activities executed during routine operation. Based on the DLR SAR calibration facility and rainforest acquisitions, the paper describes the different effects observed and gives recommendations to solve the outstanding issues. Furthermore, it is shown, that the strong radiometric requirement of Sentinel-1A is achievable.