Theory of HF and VHF Propagation Across the Rough Sea, 1, The Effective Surface Impedance for a Slightly Rough Highly Conducting Medium at Grazing Incidence

Abstract

One method of analyzing radiation and propagation above a surface is to employ an effective surface impedance to describe the effect of the boundary. In this paper an expression is derived for the effective impedance at grazing incidence of a slightly rough interface between air and a finitely conducting medium for which the Leontovich boundary condition is applicable. The perturbation technique of Rayleigh and Rice is employed, and attention is restricted to vertical polarization. The resulting effective surface impedance consists of two terms, the impedance of the lower medium when the surface is perfectly smooth and a term accounting for roughness. The latter term can be complex in general and depends on the strengths of the roughness spectral components present. The result is applicable to either deterministic periodic surfaces or random rough surfaces. Various alternate definitions of the effective surface impedance are examined and are seen to be equivalent. The analysis of power flow at the surface permits the interpretation of the interaction process in terms of scattered fields.

Propagation and scattering in MF/HF groundwave radar

“…Note also that the predicted attenuations are for a smooth sea. Barrick [10] has computed values of oversea loss due to sea roughness (see also Millman [11]). An extra two-way attenuation of 2 dB at 5 MHz and 12 dB at 10 MHz would be expected at 100 km for a sea state of 6 (wind speed 11 m/s" 1 ).…”

The Use of HF Surface Wave Propagation to Support a Data Link from an Expendable Buoy

“…E i£(band idge)I£(band center) (5) Assuming optimal impedance transformation as given by (3), equation (5) reduces to…”

“…In addition to falling at the lower end of the HF band where surface wave propagation is generally superior, these specific frequencies were chosen because at these values, Barrick [3,5,61 has estimated the propagation loss from various sea state conditions in addition to the smooth surface propagation loss for a spherical earth. Barric6's analysis of the effect of sea state is based on the use of two height-spectrum models for wind driven ocean waves: a directional Neumann-Pierson model and an isotropic Phillips model.…”

Apparent Radar Cross Section of a Large Target Illuminated by a Surface Wave Above the Sea

“…So the small perturbation method can be applied to compute the surface impedance of the rough surface. The formula of the modified impedance surface has been derived by Barrick [18,19] applying the second order small perturbation method with the Leontovitch approximation.…”