An inversion algorithm for retrieving soil moisture and surface roughness from polarimetric radar observation

A semi-empirical polarimetric scattering model for bare soil surfaces is developed. This scattering model is constructed based on the existing theoretical models in conjunction with an extensive experimental data collected with polarimetric scatterometer systems at microwave frequencies. The backscattering coefficients as well as parameters of phase difference statistics, degree of correlation (α) and polarized phase difference (ζ), are expressed in terms of both surface parameters (rms height, correlation length, and dielectric constant) and radar parameters (frequency and incidence angle). The semi-empirical model is used as a basis for an inversion algorithm to estimate the surface parameters from the polarimetric backscatter response of a surface when the radar parameters are known. By performing a sensitivity analysis, a set of optimum parameters are chosen for the inversion algorithm. It is shown that the co-polarized ratio (σ⁰ _hv/σ⁰ _vv ) the cross-polarized ratio (σ⁰ _hv/σ⁰ _vv), and the degree of correlation for co-polarized phase difference are most sensitive to the surface parameters and least affected by the measurement errors