The development and first results from the ESTEC ERS-1 active radar calibration unit

The specification and development of a microwave active radar calibration unit (ARC) used as a ground calibration reference standard for the European Remote Sensing Satellite ERS-1 imaging synthetic aperture radar are described. The first results obtained from its use as a calibration standard from the processed satellite image are given. Three such units are placed across the swath giving point target returns with a known radar return. The units have been designed for maximum stability with temperature (<0.1 dB), for absolute calibration the ARC is referenced to a flat plate using a novel technique of multiple transmission in its self-calibration mode, achieving an absolute calibration error of <0.14 dB. First results obtained from the calibration validation exercise are presented and discussed