On the composite model for rough-surface scattering

The Kirchhoff method and the small perturbation method are usually used in combination in the composite model of rough-surface wave scattering. They are shown to be identical to the first order for scattering by a perfectly conducting body of a circularly polarized incident wave into a scattered wave polarized in the expected sense of circular polarization. Thus for this case, a single application of the Kirchhoff method is as accurate as the composite model and is simpler to apply. The identity remains valid for arbitrary directions of incidence and scattering, but not for other polarizations. Statements in the literature at variance with these results appear to be based on derivations which neglect some part of the complete solution.