Forward Radar propagation over a rough sea surface: a numerical assessment of the Miller-brown approximation using a horizontally polarized 3-GHz line source

In order to reliably predict long-range radar coverage within an ocean environment, one must accurately account for the effects of ocean roughness on radar propagation. The method known as the Miller-Brown approximation is a widely used technique for computing the coherent field reflected by a rough sea surface and it is often incorporated into sophisticated numerical propagation models such as the Fourier split step algorithm of the parabolic wave equation. Nevertheless, the accuracy of the Miller-Brown approximation has not been systematically or rigorously assessed for realistic scenarios of interest to shipboard radars. We present here a first step toward this assessment by using a method of moments solution to compute the propagation factor, η, for an ensemble of one-dimensional (1-D) rough sea surface realizations having dielectric properties and roughness profiles that are consistent with a wind roughened ocean surface. The particular method of moments (MoM) technique used combines an accelerated spectral method and a multigrid iterative approach (MGIA). The MGIA results for the propagation factor η_MGIA are compared to the corresponding predictions η_MB obtained via the Miller-Brown approximation. In addition, the well-known Ament approximation is used to compute results for the propagation factor, η_A, and the results predicted by η_A are compared with those of η_MB. A heuristic numerical fitting scheme is also presented that improves the agreement between η_MGIA and η_MB and is used to facilitate the comparison between η_MB and η_A.