ASA 125th Meeting Ottawa 1993 May

1pAO9. The issue of time-varying oceanographic conditions as related to acoustics in shallow water.

Peter J. Stein

Scientific Solutions, Inc., 47 Aster Ct., Nashua, NH 03062

James K. Lewis

Atlantic Applied Research Corp., Longbeach, MS 39560

Here evidence is shown that time-varying oceanographic conditions are an important consideration in shallow water acoustic propagation. In most shallow water conditions there can be substantial temperature and salinity variations. Coastal jets and freshwater outflows can effect regions out to 40--50 km offshore. Sound-speed profiles, and thus the acoustic propagation conditions, can be highly variable in both space and time. This is shown by looking at a few examples. Oceanographic modeling was conducted using a three-dimensional numerical model for predicting the time- and range-varying conditions. The results from the oceanographic model were input into the Navy standard PE model to predict the acoustic propagation through these model test regions. The results show substantial differences in the transmission loss over time changes on the order of hours. Other issues such as bottom absorption, surface roughness effects, and reflections from a sloping bottom will also be addressed. Further modeling efforts that couple advanced oceanographic models to advanced range-dependent acoustic models are suggested.