The PolSAR response of a surface depends of multiple parameters, amongst which the variation of radar backscatter with the incidence angle and its roughness. To investigate the coupling between these parameters, we model the terrain as a layer of scatterers, defined by their position, their normal and a complex RCS. The SAR image is computed from the coherent sum of the scatterers directly in the SAR geometry. We show that a difference in backscattered energy between the polarimetric channel can be rendered by this simple modeling, and that some terrains lead to a decorrelation between the polarimetric channels.