Characteristics of the elevation angle in shallow-water negative thermocline waveguide

The modal elevation angle structure model constructed based on the Pekeris waveguides is no longer applicable since the vertical wavenumber varies with depth in the negative thermocline waveguide. According to the beam-displacement ray-mode theory, a modal elevation angle structure model suitable for the shallow water with a negative thermocline is constructed. The distribution characteristics of the elevation angle are revealed based on the model. The peak of the elevation angle structure for the surface source sound field is in the free mode region, while it is in the trapped mode region for the submerged source. The concentration of elevation angle structure distribution increases along with the frequency, while the peak position of the elevation angle structure hardly varies with range. These conclusions are verified by the simulation and sea trial results. The reliability of using elevation angle characteristics for target classification is confirmed using sea trial data.