A phenomenological model for radar signal propagation in evaporation ducts

A phenomenological model is proposed for the propagation of wideband radar pulses through an evaporation duct. The proposed model extends the previous models in two directions: (i) it presents a wideband characterization, thus removing the continuous wave hypothesis of most previous models; (ii) it fully considers the random characteristic of the geometric parameters by providing a statistical model. In particular, a statistical approach is used for the description of the rough sea surface due to the presence of wind and sea swells. The resulting model describes the duct as a random Gaussian fading channel with statistical parameters related to the surface geometrical characteristics. Both the single point statistic of the received signals and the spectral distortion of the transmitted pulses are studied by the proposed model. In particular, the coherence bandwidth is shown to depend essentially on the ratio between the surface standard deviation and the correlation length, i.e., on the local surface slope. As expected, the channel bandwidth decreases as either the sea roughness increases (larger standard deviation) or the surface decorrelates. These results apply both to TE and TM modes and both to exponential and Gaussian models assumed to describe the spatial correlation function of the surface heights.