Determination of vertical antenna pattern of high-resolution airborne SAR and radiometric calibration

An external calibration experiment was held for an airborne SAR. The paper describes the calibration experiment that uses a series of trihedral corner reflectors to calibrate the high-resolution SAR images, including antenna pattern correction and absolute radiometric calibration. In this paper, we specifically address the determination of vertical antenna pattern with multi-flight SAR imaging geometry, and discussion of the absolute calibration methods. First, three images acquired with variable off-nadir angle from 67.9~78.3, 70.9~78.4, and 72.5~79.8 degree respectively are combined to measure the antenna pattern with off-nadir angle from 67~80 degree. And then three images were relatively calibrated on the uniform standard based on the uniform antenna pattern. Secondly, the absolute calibration factor is inferred with two methods called average method and linear regression method, and the result is compared and analyzed. The experimental results show that our calibration method with several images together to acquire the large antenna pattern is feasible. And these images achieve a uniform relative calibration even though the different images have different imaging geometry and radiometric characteristics. After absolute calibration, the estimated RCS of each corner reflector basically reached agreement with the actual RCS, and the estimated error from the calibrated image for most of corner reflectors is less than 1.0dB.