ENVISAT-1 advanced synthetic aperture radar system calibration

An Advanced Synthetic Aperture Radar (ASAR) operating at C-band has been selected for the Envisat-1 payload ensuring continuity with ERS-1 and 2 AMI SAR and featuring enhanced capability in terms of coverage, range of incidence angles, polarisation, modes of operation. This enhanced capability is provided by significant differences when compared to AMI in the instrument design: a full active array antenna equipped with distributed transmit/receive modules which provides distinct transmit and receive beams, a digital waveform generation for pulse chirp generation, a block adaptive quantisation scheme and a scansar mode of operation by beam scanning in elevation. This paper will present the calibration concept proposed for ASAR and detail the different steps to derive the end to end system transfer function to allow the end user to derive locally the backscattering coefficient of the target of interest.