A review of models for scattering from rough surfaces

The objective of this report is to present results from a literature search of models for scattering of light from random rough surfaces in the IR, visible and UV wavelengths. The literature search was performed with signature management applications in mind. We have focused on methods for calculating the bidirectional reflectance distribution function (BRDF), which is an important input parameter in IR signature simulation software. The influence of surface roughness on optical signatures can therefore be studied using the scattering models. We have studied four analytical methods in more detail. These methods have been found to be amongst the most common in the literature: The Kirchhoff Approximation Method, The Method of Small Perturbations, The Integral Equation Method (IEM) and The Small Slope Approximation (SSA). Of these models, the IEM and the SSA have the largest ranges of validity. However, they are more complex and therefore more difficult to implement. The literature search also shows that all models are less accurate for grazing incidence. Another limitation is that the results have been derived for rough surfaces with Gaussian height distribution. Rather few comparisons between models and measurements have been found in the literature. Such comparisons are vital for the use of rough surface scattering models in signature modelling, which is our main interest. One important conclusion of the present study is therefore that the models should be implemented, mutually compared and validated against measured data of low signature materials.