Calibration of a polarimetric synthetic aperture radar using a known distributed target

Existing methods for external calibration of polarimetric synthetic aperture radars (SAR) are all based on point calibration targets. The quantity of interest in radar measurement of distributed targets is the backscattering coefficient which is different from the radar cross section (RCS) formulated for point targets. Therefore, in order to infer the backscattering cross section of a distributed target from a point target rigorously, the polarimetric ambiguity function of the SAR is needed. In the paper a calibration algorithm is proposed that circumvents all problems associated with the point target calibration methods. It is shown that the radar distortion parameters and calibration constant can be obtained from a distributed target with known differential Mueller matrix. The distortion parameters are then used to provide the calibrated differential Mueller matrix for the other homogeneous targets in the image. This algorithm is tested for the JPL L- and C-band SAR using four different distributed targets measured with polarimetric scatterometers