Retrieval of fully polarimetric mueller matrix under Faraday rotation effect at P band in space-borne polarimetric SAR observation

Spaceborne microwave observation of subcanopy and subsurface requires the SAR (polarimetric synthetic aperture radar) technology at lower microwave frequencies, such as P band. However, SAR observation at P band is remarkably influenced by Faraday rotation (FR) effect through ionosphere. An example in this paper illustrates why the measured polarimetric data with FR at P band cannot be directly applied to terrain surface classification. We further present that the parameters u, v, H, a, A for terrain surface classification derived from the polarimetric data without FR, which are recovered from the data with FR, can be applied to the surface classification, even there is a plusmn pi/2 ambiguity error unresolved. Based on gradual change of FR degree along geographical location, a method to eliminate the plusmn pi/2 ambiguity error is designed. Thus, the polarimetric scattering vector and Mueller matrix without FR and plusmn pi/2 ambiguity can be fully inverted from the measured polarimetric data with FR.