Assessment of the ASAR sensor radiometric quality in comparison to ERS-2 and RADARSAT-1 SAR data

The estimation of geophysical parameters from Synthetic Aperture Radar (SAR) data necessitates well-calibrated sensors with good radiometric precision. In this paper, the radiometric calibration of the new Advanced Synthetic Aperture Radar (ASAR-ENVISAT) sensor was assessed by comparing ASAR data with ERS-2 and RADARSAT-1 SAR data. By analysing the difference between radar signals of forest stands, the results show differences of varying importance between the ASAR on the one hand, and the ERS-2 and the RADARSAT-1 on the other. For recent data acquired at the end of 2005, the difference varies from -0.72 to +0.72dB, with temporal variations that can reach 1.1dB. 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 the European Space Agency (ESA) significantly improves the results of the radiometric calibration, where the difference between the ASAR and the other SARs will be lower than 0.5dB.