Study of Three-Dimensional Underwater Acoustic Propagation in the Continental Slope of South North China Sea with Sand Dunes

On the continental slope of Northern South China Sea, there are many special terrain, Sand dune. Because of this special topography, when the sound conducts underwater, it will be affected by these sand dunes and cause strong scattering and coupling effects. In this study, three different acoustic models (2D: RAM, Nx2D, 3D: FOR3D) are used to investigate the acoustic characteristic on seabed-dune terrain, and analyze coupling effect caused by the conduction under South China Sea within the coherence time. In numerical simulation, we use three-dimensional value(r, z, θ) that based on three-dimensional parabolic equation to observe the coupling effect (θ-coupling), which produced by horizontal acoustic transformation. We used mobile sound source (EMATT) during the experiments, found that the phase perturbation will make significant impact on the variation of sound pressure level (SPL). To observe the phase perturbation need to notice the complex of sound pressure and the coherence time, which defined as the duration when SPL decreases 1dB. From the comparison of simulation and experimental data. First, we found the topography of sand dunes will affect the TL and coherence time a lot. Second, the model and experiment display that there has significant difference in TL along with change of topography. Third, when the propagating way vertical with the sand dune, the coherence time is longer and can’t be find coupling effect. Forth, when the propagating way parallels with the sand dune, there has significant coupling effect from the simulation of FOR3D, In the future, plus more ocean environment, improving the initial condition in FOR3D, updating the software, correspond the actual situation of the ocean more.