Assessment of the ASAR sensor radiometric quality in comparison to ERS-2 and RADARSAT-1 SAR data
Résumé
The estimation of geophysical parameters from SAR (Synthetic Aperture Radar) 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 ASAR on the one hand and ERS-2 and RADRASAT-1 on the other. 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. Consequently, it is currently necessary to remain prudent when interpreting ASAR images calibrated for the estimation of geophysical parameters.
