Observation and modeling of three-dimensional sound propagation along a nonlinear internal gravity wave at a shelfbreak

Underwater sound propagation can be influenced by strong sound speed gradients generated by nonlinear internal gravity waves (NIWs). Additionally, the seafloor slope plays a crucial role in controlling the direction of acoustic reflections. Experimental data collected at a shelfbreak in the northeastern area of the South China Sea were analyzed to investigate the joint acoustic effects of these two environmental factors. Both two-dimensional (2D) and three-dimensional (3D) numerical sound propagation models were employed to study the observed acoustic signal variations on a hydrophone vertical line array. Comparisons between 2D and 3D sound propagation were conducted to examine changes in ray tracing paths and transmission loss associated with approaching NIWs over the sloping seafloor. 3D sound ducting between the NIW front and the bottom slope was observed to cause a significant increase in acoustic intensity, up to 9.5 dB, over a propagation distance of 4.8 km.