Electromagnetic forward scattering from two-dimensional rough sea surfaces at low grazing angles.

摘要

Low grazing, forward scattering from rough surfaces in the Radio Frequency (RF) regime is a poorly quantified phenomenon because there is limited experimental data available to aid in model development. Early rough surface, forward scattering models employed Geometric Optics (GO) theory with two rough surface reflection coefficients: one coherent and the other diffuse. The coherent is generally derived using statistical scattering arguments while the diffuse coefficient is traditionally determined experimentally. Later efforts invoked Physical Optics (PO) for high grazing angles. However, the GO and PO models are unable to capture the effects of shadowing and multiple interactions that occur near grazing and for very rough surfaces. With the advent of more powerful digital computers, modeling efforts shifted towards rigorous integral methods to determine the forward scattering. However, the large memory requirements and computation times associated with these methods make them impractical for full-scale applications.; The primary goal of this research is to develop viable, general, and validated rough surface forward scattering models at low grazing. Secondary goals are (1) to observe and understand forward scattering phenomena at low grazing, (2) to construct an experimental, forward scattering validation database, and (3) to accelerate rigorous modeling methods useful in rough surface scattering calculations. These goals are accomplished by experimental observation of forward scattering, theoretical development of 2D, rough surface scattering models, and the numerical simulation of conditions within the experimental database.; The experimental portion consists of a unique, low grazing, forward scattering measurements for a variety of controlled two-dimensional, scaled sea surfaces. This measurement was the first to include simultaneous, detailed profiling of the water's surface. Two high frequency models are developed to account for shadowing effects observed in the experiment. An additional model, based on the rigorous Method of Moments (MoM) utilizing specialized basis functions, is applied to solve the scattering problem. To increase the efficiency of the integral method, I developed the Moments via Integral Transform Method (MITM) to significantly reduce matrix fill times. Lastly, validation of the forward scattering models is done via comparisons between the measured and simulated results.