Development of the ERS-1 active radar calibration unit

The development of a microwave active radar calibration unit (ARC) to be used as a ground calibration reference standard for the European Remote Sensing Satellite ERS-1 imaging synthetic aperture radar is described. Three such units are placed across the radar swath, giving point target returns with a known signal strength, and are used to calibrate the radar image. The units have been designed for maximum stability with temperature (<0.1 dB over the temperature range of -15 degrees C to +35 degrees C). 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.<>