Polarimetric Calibration Scheme Combining Internal and External Calibrations, and Experiment for Gaofen-3

The parameters for polarization distortion of spaceborne polarimetric synthetic aperture radar (SAR) have range-dependence (or look-angle-dependence), which requires a polarimetric calibration to be performed at any look-angle. It is a huge endeavor to rely solely on ground experiments to obtain a polarimetric calibration at all look-angles. For SAR with phased array antennas we deduce, based on the model for the general polarimetric system, the model for fine polarization distortion described by the parameters of the radar device under the condition of high polarization isolation. We point out the mechanism that causes both variable and constant polarization distortions, and we deduce the correction algorithms for the two types of polarization distortion. Then we propose a polarimetric calibration scheme combining internal and external calibrations to calibrate the two types of polarization distortions for SAR with phased array antennas. The scheme uses the internal calibration data of the radar and the model of the antenna pattern established before satellite launch to invert the in-orbit antenna patterns to correct for the variable polarization distortion, and it needs only a small amount of calibration equipment to solve for the parameters for constant polarization distortion. The scheme no longer depends on the distributed target and improves the polarization precision of the data. It is applied to the calibration experiment for the data processing of the GaoFen-3 satellite and has achieved good results in applications.