Polarimetric Calibration for a Ground-Based Radar, and Comparison of the Polarimetric Parameters with Air-Borne SAR Obtained from a Forest

A polarimetric ground-based radar (GB-radar) system operated in the L-band has been developed. The frequency range of GB-radar is 1.215 to 1.3 GHz, which is the same as that of Japanese satellite-borne SAR, PALSAR-2 (Phased Array type L-band Synthetic Aperture Radar), and Japanese L-band air-borne radar, i.e., Pi-SAR-L2 (Polarimetric and Interferometric Airborne Synthetic Aperture Radar L2). Polarimetric calibration was carried out twice in the field to calibrate and validate the GB-radar data. Cross-talk and channel imbalance are improved for the both experiments, and are from −13.3 dB to −30.7 dB, and from 1.06 to 1.00, respectively for the first experiment, after calibration. The calibrated cross-talk and channel imbalance values were comparable to −31.7 dB and 1.013, which were obtained using PALSAR. Radiometric calibration and antenna pattern correction were also carried out in the second experiment. Forest observations were also carried out simultaneously by GB-radar and Pi-SAR-L2 in the second experiment. The range profiles obtained by GB-radar and Pi-SAR-L2 were compared for several polarimetric parameters, namely, radar backscattering coefficient, polarimetric coherence, eigenvalue-decomposition parameters, and four-component-decomposition parameters. Both range profiles matched moderately well and showed good performance that could compensate for the limited possibility of satellite/air-borne SAR observation.