Assessment of Tropospheric Effects for Calibrating precisely Space-borne SAR Systems

Abstract

For space-borne SAR systems operating in X-band and beyond, the propagation media along the propagation path may distort SAR measurements. In order to meet the high demand on radiometric accuracy, tropospheric attenuation effects have to be taken into account during the external calibration procedure. Especially in X-band it is well known that the attenuation caused by heavy precipitation events may reach values up to about 30 dB. In this contribution it is shown how the calibration of SAR-systems is influenced by weather (precipitation) and how the radiometric accuracy can be improved by taking the atmospheric conditions into account. A concept is introduced that has been applied during the commissioning phase of the German TerraSAR-X satellite. By acquiring simultaneously ground-based weather radar data and the SAR acquisitions it was possible to flag affected SAR images and to exclude them from the procedure to derive the absolute calibration factor. Thus, the precision of calibrating TerraSAR-X could be improved yielding a high radiometric accuracy of 0.31 dB in strip-map mode acquisition.