Effect of Rough Sea Surface on Electromagnetic Wave Propagation in Evaporation Duct Environment

Atmospheric duct is a unique condition at sea that enables over-the-horizon detection by radio equipment. However, the ocean waves caused by sea breezes on the ocean surface significantly diminish this effect. In this paper, the influence of a rough sea surface on the propagation of electromagnetic (EM) waves is analyzed using the parabolic equation (PE) model. The analysis considers the rough sea surface model with and without accounting for the wave shadowing effect. Firstly, the study employs the Shadowed model, which considers the effect of shadowing, along with the Ament model, which neglects the effect of shadowing. These models are used to analyze the impact of grazing angle and wind speed (WS) on the roughness reduction factor and the Fresnel reflection coefficient of smooth surfaces. Secondly, the measured meteorological gradient data obtained from a research vessel in the South China Sea are utilized to analyse the effects of smooth sea surface and two types of rough sea surface on the one-way propagation loss under different WS conditions. The results show that as the WS increases, the influence of a rough sea surface on EM wave propagation within the evaporation duct becomes more pronounced, which will cause higher propagation loss. The rough sea surface on the propagation loss up to an increase of nearly 27.39 dB compared to a smooth sea surface.