Bathymetric and oceanic variability effects on acoustic propagation metrics in a shelf-break environment

Abstract

The interaction of oceanographic variability and bathymetry on acoustic propagation in the littoral is quite complex, and the relative importance is not readily quantified, especially for data-model comparisons. Sound speeds derived from ocean models could be compared directly to experimental sound-speed data, but this is a crude measure of environmental impact on acoustics. Instead, a 300-Hz source in a three-dimensional parabolic equation (PE) acoustic propagation model provides input to proposed acoustic metrics, especially related to array performance, to assess the effects of experimentally derived bathymetry and tide. The metrics can also be used for comparison of an ocean model and experimentally derived sound-speed profiles. Other acoustic mode metrics can be derived and compared to the more computationally intensive three-dimensional PE derived measures. As an example, the Navy Coastal Ocean Model (NCOM), a mesoscale oceanographic model, predicts sound-speed gridded on the order of 5 m in depth and 200 m in range at 6-h updates for the ASIAEx South China Sea site. This can then be used for metric calculations and data-model comparison. [This research is sponsored by the ONR.]