SIMPLE MODELING 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 developme nt of simple backscattering soil models which can account for the vari ations of incidence angle observed in the same picture or in multiangl e systems. A correction factor for the variations of incidence angle i s therefore coupled with a classical linear model of the variation of backscattering coefficient with surface soil moisture in a four-parame ter model. The correction factor is based on the cosine-type behaviour of the backscattering coefficient as a function of incidence angle, w hich is observed for rough agricultural surfaces. This simple model is tested on radar measurements performed over a large range of radar co nfigurations. The model is shown to reproduce correctly the observed v ariations of the radar signal with incidence angle and soil moisture. Its parameters have a physical sense and vary as expected, from litera ture, with frequency and polarization. When tested on data simulated b y the analytical Integral Equation Model, the results of the cosine mo del are confirmed, as well as the variation of its calculated paramete rs with frequency and polarization. The inversion of the model with th e angular correction factor shows that the cosine model allows the ret rieval of soil moisture with a precision of about 20 per cent of the v alue at C band and at HV and HH polarization.