Characterization of coastal environments for acoustic models

Accurate modeling of the propagation of acoustic energy in coastal waters is essential to many military and commercial applications, but unique challenges exist. The shallow water depths ensure significant boundary interactions, and the spatial/temporal variability of the water column places further demands on model capabilities. Physics-based acoustic models are evolving to allow for inputs that bring increased fidelity in the representation of the complex physical environments characteristic of littoral areas. Characterizing the environment in 4D must be accomplished as the first essential step in achieving accurate acoustic modeling. Historical databases managed by the Naval Oceanographic Office offer global coverage for parameters required for acoustic model calculations. However, the spatial and temporal resolution cannot dependably represent instantaneous conditions, and modeled acoustic propagation can be very different from actual measurements. Synoptic products generated from remote sensors or assemblages of point observations can represent a significant improvement in the fidelity of the environmental inputs to acoustic models. These products have some shortcomings, as well. The spatial resolution is often considerably lower than the environmental variability, product senescence can be a factor for dynamic characteristics, remote sensors may have observations obscured, and synoptic oceanographic parameters are often derived indirectly from parameters with complex associations. In-situ measurements provide the most accurate, and direct, measurement of environmental parameters for acoustic modeling, but resource costs are high relative to the data gathered, and there may be overwhelming political and physical constraints to on-scene surveys. Climatology, synoptic products, and in-situ measurements represent an increasing fidelity in characterization of the environment, but with a steep collection, management, and distribution cost relative to coverage. Military applications are considered