Measurement and calibration of differential Mueller matrix of distributed targets

A rigorous method is presented for calibrating polarimetric backscatter measurements of distributed targets. By characterizing the radar distortions over the entire mainlobe of the antenna, the differential Mueller matrix is derived from the measured scattering matrices with a high degree of accuracy. It is shown that the radar distortions can be determined by measuring the polarimetric response of a metallic sphere over the main lobe of the antenna. The radar distortions are categorized as distortions caused by the active devices or distortions caused by the antenna structure (passive). Since passive distortions are immune to changes once they are determined, they can be used repeatedly. The active distortions can be obtained by measuring the sphere response only at boresight, reducing the time required for calibration under field conditions. The calibration algorithm was applied to backscatter data collected from a rough surface. The results indicate that removal of the radar distortions from the cross products of the scattering matrix elements cannot be accomplished with traditional calibration methods