LONG TERM GOALS

The long-term goal is to better understand fluctuating sound propagation in two distinct ocean acoustic regimes: Stratified shallow water, where sound is highly bottom interacting, and the temperate deep-ocean sound channel. Acoustic field fluctuations have time scales varying from less than a minute to hours, and horizontal spatial scales from tens of meters to kilometers, comparable to processing time scales and system spatial scales, and thus impact exploitation of underwater sound. With proper understanding, reliable predictions of temporal and spatial variability of received underwater sound may be possible, thus improving processing and handling of signals of interest. Processing could include remediation of signal degradation and exploitation of available sonic information. OBJECTIVES An objective is to explain underwater sound fluctuation behavior that has been observed in both shallow and deep regimes. For shallow water, we seek to understand the mean and variability of transmission loss and phase at frequencies from 50 to 3000 Hz. For the deep-ocean sound channel, the objective is to better characterize coupled-mode propagation at 50 to 100 Hz over 100’s to 1000’s of kilometers. Propagation and forward scattering models, theoretical and computational, will be used to generate and to test hypotheses. Therefore, making better models is a second (enabling) objective. APPROACH The planned approach for the three-year project includes analysis of acoustic propagation variability signatures in preexisting datasets and comparison of these signatures with expectations derived from theory and models. Part of the final year will be dedicated to the planning of a potential future experiment to address questions that remain unanswered by this effort. Data from multiple recent field exercises have been analyzed. For shallow water studies, data ar