Studying Sound Propagation over South China Sea Upper-slope Sand Dunes Using Parabolic Equation Models

There are many underwater sand dunes caused by the internal wave located in the depth of 160 meters to 600 meters in northern South China Sea. The largest amplitude of these sand dunes is about 16m. Underwater acoustic transmission is affected by this topographic feature, and also has three dimensional effects. In this research the 2-D and 3-D underwater acoustic propagation models (RAM and FOR3D respectively), are used to simulate acoustic propagation in the region. There is starter issue to be resolved for the high-impedance, low-loss ocean bottom of the region. RAM with self-starter is overly initialized, thus the initial field is produced to match with the source beam-pattern. A tunable Gaussian starter is then used to avoid over initialization, which is a proper starter for the moored source. The acoustic field received at VLA emitted from the moored source is simulated with the proper starter. Results show temporal variations with respect to that of water column, and three dimensional effects over sand dunes.