Extraction and analysis of three-dimensional sound scattering characteristics by body-generated internal waves

Abstract

The motion of an object submerged in a stratified fluid generates surface wakes, and simultaneously induces internal waves at the interface where there is a change in sound speed, known as the thermocline. As a result, spectral-temporal fluctuations occur in both the surface height and the distribution of sound velocity. While surface wakes primarily contribute to geometric acoustic scattering, the internal waves generated by the underwater object's motion can have diverse effects on sound propagation, leading to a prolonged acoustic impact that may have practical applications in underwater acoustic detection. This paper investigates the impact of body-generated internal waves on underwater acoustic propagation through the establishment of an “unfrozen field,” range-dependent model using the approximated Kelvin wake theory. The model allows numerical simulations to demonstrate the spatial-temporal coherence, time-frequency modulation and directional characteristics of the three-dimensional sound field scattered by the body-generated internal wave. By analyzing the influences of thermocline depth, target motion velocity and source depth, the results presented in this study indicate that the long-range acoustic propagation, modulated by the body-generated internal waves, can provide additional information for detecting moving targets.