Abstract
A description is given of an over-sea radio-wave propagation model involving strongly shadowed parts of the sea surface. This model is of great practical consequence, since the present-day imperative of the fundamental science is to explore physical processes occurring during the wave propagation. The currently used calculation of e.m. field over the sea surface with wind-generated waves at low grazing angles are based on the hypothesis that surface roughness (sea waves) results from the perturbation (on the average) of the planar interface and exhibit minor slopes. However, in practice these radio-wave propagation conditions do not occur ever so often. We have investigated an alternative incident that is clearly indicate of strong shadowings. The shadowed surface areas preclude the reflection from quasi-planar near-horizontal, surface elements. The received data provide a totally new insight into the physical processes (mechanisms) during radio-wave scattering under strong shadowing conditions. We have made use of the numerical simulation method to determine the coordinates and the curvature of unshadowed elements which represent the wave crests. The field being reradiated by these elements is shows to be the result of the Fresnel diffraction effect and the reflections from the convex cylindrical surfaces (in the 2-D case under study). As far as Ka-band radio waves (8-mm-wavelength), we have assessed the reradiation-power path-length distribution, angular spectra of waves arriving at the receiving-antenna aperture. The knowledge of these parameters is required to analyze the direction finder operation. The authors of the present paper have revealed and analyzed the characteristic features of path length distribution and the distribution of angles of arrival (at a receiving point) of coherent and noncoherent sea surface-reradiated field components, the latter significantly affecting the accuracy of systems for measuring the angular coordinates of radiation sources, including the new modern methods of spectral evaluation.
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