Maximization of the degree of polarization to estimate the polarization orientation angle from PolSAR data: An insight into the real and complex rotation of the coherency matrix

Abstract

The angle of rotation of any target about the radar line of sight (LOS) is known as the polarization orientation angle. The orientation angle is found to be non-zero for undulating terrains and man-made targets oriented away from the radar LOS. This effect is more pronounced at lower frequencies (eg. L- and P- bands). The orientation angle shift is not only induced by azimuthal slope but also by range slope. This shift increases the cross-polarization (HV) intensity and subsequently, the covariance or the coherency matrix becomes reflection asymmetric. Compensating this orientation angle prior to any model-based decomposition technique for geophysical parameter estimation or classification is crucial. In this paper, a new method is proposed to estimate the orientation angle based on the maximization of the degree of polarization. The proposed method is then used to infer the change in the degree of polarization with the associated orientation angle.