Assessment of the Asar Sensor Radiometric Quality in Comparison to Ers-2 and Radarsat-1 Sar Data

The estimation of geophysical parameters from SAR data necessitates well calibrated sensors with good radiometric precision. In this paper, the radiometric calibration of ASAR/ENVISAT sensor was assessed by comparing ASAR data with ERS-2 and RADARSAT-1 SAR data. With regard to recent data, acquired at the end of 2005, the difference varies from -0.72dB to +0.72dB, with temporal variations that can reach 1.1dB. As for older data, acquired in 2003 and 2004, we observe a sharp decrease in the radar signal in the range direction, which can attain 3.5dB. The use of revised calibration constants provided recently by ESA (European Space Agency) significantly improves the results of the radiometric calibration, where the difference between ASAR and other SARs will be lower than 0.5dB.