Polarimetric decomposition of C-band SAR data for soil moisture retrieval over agricultural fields

Considering the surface roughness at C-band which is beyond the physically validity range of Bragg and X-Bragg scattering model, this study investigates the extension of polarimetric decomposition from L- to C- band for soil moisture retrieval over vegetated agricultural fields. The volume scattering component is first removed from the full polarimetric SAR data, then the Oh 1992 model is used to retrieve the soil moisture from the remaining coherency matrix, instead of Bragg or X-Bragg model. The proposed method is evaluated using the time series of RADARSAT-2 data and simultaneous ground measurements collected in the framework of SMAPVEX12 (Soil Moisture Active Passive Validation Experiment in 2012). A low dihedral scattering mechanism less than 5% was found for the whole investigated period due to the weak penetration depth of microwave at C-band. Thus the remaining ground matrix is mainly dominated by the surface scattering mechanism. Finally, the proposed method can retrieve the soil moisture of the fields covered by canola, corn and soybean, except for the wheat fields. An overall RMSE of 0.07 m
³
/m
³
is obtained, indicating the potential of C-band polarimetric decomposition for soil moisture retrieval.