Mode Coupling Due to a Local Inhomogeneity in a Shallow-Water Acoustic Waveguide in a Broad Frequency Band

Analytically and by numerical simulation, we consider the effect of a local inhomogeneity on a broadband (50–250 Hz) sound field formed in a shallow-water (40 m) waveguide on a stationary track at a range of up to 5 km. Analytical estimates are obtained using mode coupling theory, and numerical simulation is carried out using the wide-angle parabolic equation. It is assumed that the sound source is a single omnidirectional emitter, and the receiving system is a vertical array spanning the entire waveguide over depth. As an inhomogeneity, a local change in thickness of the water layer or a internal wave soliton is chosen, the presence of which causes mode coupling. Analytical estimates and numerical simulation show that when there is a local inhomogeneity on the acoustic track, the frequency dependence of the mode amplitudes acquires a characteristic modulation, the period of which decreases in frequency domain with increasing of the distance from the sound source to the inhomogeneity. This effect can be used to determine the position of a local inhomogeneity on a stationary track.