A Reflection Symmetry Approximation for Freeman-Durden Decompostion of Polsar Data

Freeman-Durden decomposition is a frequently used technique to analyze the scattering characteristics of multilook Polarimetric Synthetic Aperture Radar (POLSAR) data. When it is applied to real POLSAR data, two problems emerge, which are the volume scattering overestimation and negative powers. Many researchers think these two problems are caused by the insufficient decomposition algorithm, and several improvements are proposed. However, the improved decomposition algorithms become more and more complicated, and some new problems such as the decomposed component is not model-based also emerge. In this article, we try to solve the two problems through another way. We think they are caused by the dogmatic input rather than the insufficient decomposition algorithm. Freeman-Durden decomposition explicitly assumes reflection symmetry. Its input is a direct truncation of the measured coherency matrix. The truncation can be regarded as a Reflection Symmetry Approximation (RSA) of the measured coherency matrix. We firstly show some reasons why we think the truncation is not a good RSA. Then a new RSA is proposed based on the sum of three reflection symmetry components derived from the measured coherency matrix. Experimental results with several real POLSAR images show that, if the new RSA is used as the input of Freeman-Durden decomposition, the abovementioned two problems no longer exist.