1. Introduction
With the realization of fully polarimetric synthetic aperture radar (PolSAR) imaging systems, polarization diversity has received a tremendous boost and becomes common in spaceborne SAR. A three-component scattering model was developed by Freeman and Durden [1], [2] for multi-look PolSAR data. Their model involves physical fitting of a combination of double-bounce, surface, and volume scattering mechanisms. Yamaguchi et al. [3] extended the Freeman-Durden model by adding helix scattering. One well-known problem associated with the model-based decomposition is the presence of negative scattering powers [3]–[8], which is inconsistent with the actual scattering phenomenon.