Three Dimensional Underwater Acoustic Propagation in Continental Slope Regions with Sand Dunes in South China Sea

There are many underwater sand dunes in the upper continental slope at the depth of 160m to 600m in northern South China Sea. These sand dunes are special as they are the largest sand dunes observed with amplitude up to 16m. Underwater acoustics transmission will be affected by these sand dunes and in turn produce the three dimensional effects. Due to the variation of topography in this area, if we use the 2-D (r,z) model, it will ignore the variation of horizontal direction and cause the θ-coupling disappear, causing us unable to describe the three-dimensional effects of the sand dunes completely. So, the 3-D underwater acoustic propagation model, FOR3DW (based on the cylindrical coordinates, the wide-angle version of FOR3D) is used to analyze the 3D effects caused by the sand dunes in South China Sea. In order to identify the causes generating 3D effects, ideal sinusoidal topography of different amplitudes, crest-to-crest intervals, and angles between the propagation direction and the orientation of dunes are studied. Then the actual environmental inputs from the experimental sites in the northern South China Sea are used to do the 3D calculations, which are used to plan for 3D acoustic propagation in the experiment conducted in June 2014. The 3D simulation is compared with the experimental data. Good match of data and simulation are found in some periods, while there are discrepancies in other time which demands future investigation.