An Adaptive PolSAR Trilateral Filter Based on the Mechanism of Scattering Consistency

Polarimetric synthetic aperture radar (PolSAR) can record the backscattering information of ground objects by capturing the phase difference of echo signal in different polarization combinations. Due to the characteristics of coherent imaging, there is a lot of coherent speckle noise in PolSAR images. However, most of the current PolSAR image despeckling algorithms are difficult to balance the ability in aspects of speckle suppression, polarization information retention, and edge structure preservation. This article proposes an adaptive PolSAR trilateral filter (PTF) based on the mechanism of scattering consistency, which consists of the following three steps: 1) the marker map of ground object scattering category is first obtained based on the dominant scattering mechanism determined by Freeman decomposition of the polarization covariance matrix; 2) next, the neighborhood pixels with the same scattering mechanism as the center pixel are screened out within an adaptive filtering window; and 3) a PTF is established through integration of the spatial proximity, polarization similarity, and local structural characteristics of the center pixel and the screened pixels to effectively suppress the speckle noises. Experimental results upon the data of Radarsat-2 and airborne synthetic aperture radar (AirSAR) demonstrate that PTF can not only suppress coherent speckle noise effectively without sacrificing the edge structure information but also retain the unique polarization information of PolSAR image. In particular, compared with the traditional six widely used PolSAR despeckling algorithms, PTF has been significantly improved in terms of equivalent number of looks (ENLs) and degree of difference (Dod) indexes by 2.49 times and 6 orders of magnitude, respectively.