Average irregularity representation of a rough surface for ray reflection

A new ray model is presented for the reflection of electromagnetic radiation from the rough air-material interface of a randomly rough surface. Unlike previous derivations that modeled the rough interface as consisting of microareas randomly oriented but flat (facets), this derivation models it as consisting of microareas not only randomly oriented but also randomly curved. Physically, the models are the same, but this new derivation leads to some new results. (1) For any given rough surface, there exists a single, optically smooth, curved surface of revolution of very restricted shape that will reflect radiation in the same distribution as that reflected by the rough interface. (2) Modeling that surface as an ellipsoid of revolution gives a surface-structure function that appears more accurate and useful than existing ones. (3) Unlike the facet derivations, this derivation lends itself to a normalization that gives the absolute, instead of just a comparative, reflectance-distribution function.