Evaluation of Gaofen-3 C-Band SAR for Soil Moisture Retrieval Using Different Polarimetric Decomposition Models

Soil moisture is a key parameter affecting crop growth. Gaofen-3 satellite is the first C-band synthetic aperture radar produced by China, which provides full-polarization data sources for soil moisture estimation. This article evaluated the potential of estimating soil moisture via GF-3 SAR over agricultural area using different polarimetric decomposition models, namely, the modified Freeman–Durden model (MFDM), the An model and the FDM. Among them, the MFDM is the first attempt to be used for soil moisture retrieval. After removing the volume scattering, the surface and dihedral scattering component were used complementarily to estimate soil moisture. The results show the performance of each polarimetric decomposition models for soil moisture estimation depends on the crop type, crop growth stages and soil moisture conditions. Soil moisture retrievals exhibit an overall underestimation with a root mean square error of 8–11vol. %. This is mainly because of the random orientation assumption in the volume scattering model, which cannot accurately describe the variability of the crop structure. Due to the application of de-orientation process and power constraint, the MFDM shows the best performance both for corn and wheat, with inversion rates of 39%–45%.