On the use of the specular direction copolarised ratio for the retrieval of soil dielectric constant

In this paper we propose a soil dielectric constant retrieval scheme based on the use of the ratio of power densities scattered at hh and vv polarisations along the specular direction for different incidence angles and/or frequencies. The method relies on the minimum squares technique, and is based on the observation that, at variance with the backscattering case, in the specular case the small perturbation method (SPM) and the Kirchhoff approach (KA), both under the scalar approximation (SA) and under the stationary phase approximation (SPA), lead to the same expression of the copolarised ratio, that should hold under a wide range of surface roughness. We present method of moments (MoM) simulations that confirm this expectation, and we test the validity of the overall retrieval scheme.