Calibration experiments of ERS-1 SAR with active radar calibrator in Japan

The authors carried out calibration experiments of the C-band synthetic aperture radar (SAR) of the first European Remote-Sensing Satellite (ERS-1) with its three passes over Japan in June, July, and August 1993, employing an active radar calibrator (ARC) and a corner reflector (CR) both located in the site of Kashima Space Research Center (140°40´E, 35°57´N) of the Communications Research Laboratory. The ARC has a large radar cross section (RCS) of over 60 dBm², with a function to shift the frequency of signals when retransmits that makes the position of the ARC shift in the SAR image. Frequency shifts of the ARC were set to 0, 200, 400 Hz for the three passes each, so that the ARC echo should appear at 0, 640, 1280 m shifted in the azimuth direction from its actual location in each SAR image. Received power by the ARC was recorded during the overpasses, which shows an antenna pattern of the SAR. The authors also used a corner reflector of 1.1 m square trihedral (RCS=42.4 dBm²) as a landmark, as well as another calibration target. Obtained SAR image data processed by National Space Development Agency of Japan (NASDA), the authors have examined image amplitude (data numbers) and locations of both of the ARC and the CR. It is seen in the SAR images, as expected, that the positions of the ARC are shifted depending on the shift of frequency