A further study of the IEM surface scattering model

The IEM surface scattering model was developed based on an approximate solution of a pair of integral equations governing the surface current. Among the assumptions leading to the approximation is the use of a simplified expression for the Green's function in spectral form. In particular, it was argued that the absolute value of the difference in the surface heights at two surface points appearing in the phase of the Green's function can be ignored. This argument was arrived at by noting that (i) if the two points are close together, the difference in heights should be small and (ii) if the two surface points are far apart, there should be a negligible amount of correlation between the two points and hence will not contribute significantly to the scattered power. Mathematically, there is no reason to make this assumption and it is also questionable whether the contribution from two surface points that are neither near or far can always be ignored. In this paper the authors want to remove this assumption by keeping this phase term and examine the difference in scattering calculations with and without it. It is found that in all cases considered the existing IEM model gives satisfactory predictions in single scattering. However, in multiple scattering calculations it is not possible to ignore this phase especially for surfaces with large roughness. An application of this model to scattering from known rough dielectric surfaces acquired at the EMSL of the JRC at Ispra is shown and good agreements are realized. Further application to a large slope surface that causes backscattering enhancement also gives good agreement with data.