Simple modelling of radar backscattering coefficient over a bare soil: variation with incidence angle, frequency and polarization

As a basis for inversion algorithms, there is a need for the development of simple backscattering soil models which can account for the variations of incidence angle observed in the same picture or in multiangle systems. A correction factor for the variations of incidence angle is therefore coupled with a classical linear model of the variation of backscattering coefficient with surface soil moisture in a four-parameter model. The correction factor is based on the cosine-type behaviour of the backscattering coefficient as a function of incidence angle, which is observed for rough agricultural surfaces. This simple model is tested on radar measurements performed over a large range of radar configurations. The model is shown to reproduce correctly the observed variations of the radar signal with incidence angle and soil moisture. Its parameters have a physical sense and vary as expected, from literature, with frequency and polarization. When tested on data simulated by the analytical Integral Equation Model, the results of the cosine model are confirmed, as well as the variation of its calculated parameters with frequency and polarization. The inversion of the model with the angular correction factor shows that the cosine model allows the retrieval of soil moisture with a precision of about 20 per cent of the value at C band and at HV and HH polarization.