Normal Mode Coupling of Broadband Acoustic Field in a Shallow Water Waveguide with a Sloping Bottom and Thermocline

The paper presents a theoretical and numerical study of the sound field mode structure in a wide frequency band (0.2–2 kHz) in a wedge-shaped waveguide with a gradient sound speed profile, associated with the presence of a thermocline. The acoustic track is directed towards increasing depth, so that the sound source and the vertical receiving array of hydrophones are located on different sides of the region where the thermocline touches the bottom. It is shown that in this region, due to mode coupling, the frequency dependences of the amplitudes of normal modes acquire an oscillating character, and the oscillation period depends on the depth of the thermocline. Analysis of the oscillation spectrum of lower mode amplitudes allows us to estimate the distance from the sound source to this region.