An improved IEM model for bistatic scattering from rough surfaces

In the development of the IEM model for surface single scattering a simplifying assumption was applied to the phase of the Green's function in the average power calculation leading to a surface scattering model in algebraic form. In this paper we remove this simplifying assumption yielding a more complex model but still in algebraic form. We shall show that the assumption used in the past does not cause an appreciable difference when the incident and scattered angles are close to each other. However, for different incident and scatter angles there is a noticeable difference especially when the surface roughness is small and scattering is weak. For surfaces with large scale roughness the difference between the original IEM and the improved IEM is generally negligible. Bistatically, the improved IEM is in good agreement with the standard small perturbation model in the low frequency region and with the standard Kirchhoff model in the high frequency region. A recent publication extending the original IEM model along a different direction is shown to be a more restrictive surface scattering model in terms of applicability to moist rough surfaces.