Modeling evaporation duct propagation above the rough sea surface with the aid of the parabolic equation and ray optics methods

The problem of propagation above the rough sea surface in an evaporation duct environment has been received considerable attention. The current propagation model above the rough sea can lead to an overestimation of the radar detection range. An alternative method is the boundary integral equation (BIE) method. However, the BIE is not an efficient computationally. In this paper, a fast hybrid modeling technique is presented to model the evaporation duct propagation above Gaussian rough sea surface. The technique uses a combination of Fourier split-step (FSS) parabolic equation (PE) method and ray optics (RO). In this technique, the Ament boundary condition with shadowing effect is used at grazing angle. The examples analyze the influence of the shadowing effect of rough Gaussian surfaces on the evaporation duct propagation. The results indicate that the propagation modeling with the shadowing effect reduce this overestimation, when the wind speed exceed 5 m/s, the shadowing effect will influence the propagation, the propagation loss will become larger with the wind speed increasing, and when the duct height is between 10 m and 20 m, the influence of shadowing effect on the propagation will be the most obvious. Furthermore, for combinations of high frequencies, high duct heights and high wind speeds, models indicate that wind-driven surface roughness can reduce the effectiveness of the evaporation duct.