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Evaluating the effects of antenna radiation pattern in processing coherent backscattering from rough surfaces Open Access

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Evaluating the Effects of Antenna Radiation Pattern in ProcessingCoherent Backscattering from Rough SurfacesThe research presented herein is an analytical and numerical investigation of the effects of spatial coherence of an irregular air/dielectric interface on the backscattered electromagnetic radiation when the interface is illuminated and received by an antenna beam with a surface footprint much larger than the correlation length of the irregularities. Even though the formulation is sufficiently general and, consequently, would be also applicable to scattering from any terrain, the focus of the proposed research will be the air/sea interface with an eventual specialization to radar clutter at low grazing angles. The formulation employed is based on the results of W. Wasylkiwskyj, (“A New Formulation for Coherent Backscattering from Distributed Targets,” 2007 IEEE Antennas and Propagation International Symposium, June 14, 2007) and W. Wasylkiwskyj and J. Alatishe, (“Coherent Scattering from Distributed Targets,” IEEE MRRS-2008 Symposium Proceedings, pp. 36-41). The received wave at the antenna port is computed in terms of a “generalized” scattering cross-section per unit area.Unlike the conventional scattering cross-section per unit area employed in radar clutter calculations, the generalized cross section depends on both the statistical properties of the surface and the antenna radiation field. In the special case of spatially uncorrelated surface irregularities this generalized cross-section becomes independent of the antenna characteristics and, indeed, reduces to the conventional “σ0 “cross-section per unit area. Thus the generalized cross-section can serve as a metric of the degree of the spatial correlation of the surface.The scattering matrix of the surface used in this formulation is derived under several different sets of approximating assumptions: small amplitude, small slope, physical optics, and a “two-scale” model. For the small amplitude approximation, numerical results indicate that correlation in the surface can give rise to significant deviations from the standard “σ0 “ results based on the Bragg Scattering model. The small slope approximation was implemented numerically and the results indicate that spatial coherence in the backscatter induces a noticeable effect in the detected response . The small slope approximation is particularly suitable to the study of scattering by the ocean, since small wave slopes represent the typical state of the ocean. Computations were carried out for a variety of ocean surface wave spectral models. The results of these computations, in conjunction with radar back-scattering data will be employed to validate the new numerical predictions with particular emphasis on small grazing angles

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