1. Introduction
PolSAR is a multi-dimensional imaging system with all-day, all-weather and high-resolution. PolSAR backscattering returns can be represented as HH, VV and HV polarizations for distributed targets. Due to the correlations of polarimetric channels, speckle effect affects not only three intensities, but also three phases [1]. To reliably interpret PolSAR, the speckle must be reduced.