In this paper, we propose a fine scale partially coherent patch model (FPCP) for GNSS-R land applications for soil moisture retrieval. The land surface is divided into coherent planar patches on which microwave roughness is superimposed. The scattered waves of the coherent patch are decomposed into the coherent specular reflection and diffuse incoherent scattering. A fine scale of 2 meter patch size is chosen for the coherent patch to be applicable to complex terrain with large varieties of topographical elevations and with small to large topographical slopes. The summation of scattered fields over patches is carried out using physical optics. The phase term of the scattered wave of each patch is kept so that correlation scattering effects among patches are accounted for. Results are illustrated for power ratio for areas near the specular point and areas far away from the specular point. Comparisons are made with the radiative transfer geometric optics model. DDM simulations are performed with good agreement with CYGNSS data.
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