Impacts of Small Scale Ocean Dynamics on Sound Energy Propagation in Areas of Strong Stratification

Emanuel F Coelho, Applied Ocean Sciences, LLC, New Orleans, LA, United States, Kevin D Heaney, Applied Ocean Sciences, LLC, Fairfax Station, United States and Martha Schonau, Scripps Institution of Oceanography, La Jolla, United States
Abstract:
Strong gradients between water masses in the ocean, when subject to complex dynamics and forcing like those produced by tides, wind forcing and large-scale dynamical instabilities, can trigger inhomogeneities that can produce small-scale (range of 1 kilometer to 10thskilometers) fronts. These features can trigger critical horizontal grazing angles for sound energy propagation larger than 10deg, suggesting that sound could be strongly refracted and produce areas of stronger and weaker sonification, along with changes in the bearings, time delays of acoustic arrivals and change multi-path characteristics. Thus, these small-scale processes introduce complex acoustic propagation prediction challenges like 3-dimensional effects and sharp loss/gain changes along levels and directions. At present, most of the operational ocean forecast systems and data assimilation solutions do not have the skill to deterministically resolve these processes. When present, these features may cause inaccuracies in Navy tactical decision tools and severely impact the accuracy of algorithms using sound propagation to estimate ocean volumes states (e.g. ocean tomography or data assimilation). This work outlines and proposes a framework to diagnose these processes, following an operational risk management approach. It uses real-time ocean data and ocean model forecasts, to build diagnostic variables estimating the possible acoustic impacts of local small-scale frontal systems and instabilities. This framework can either be used to select numerical solution approaches and/or sampling strategies to characterize the ocean-acoustic environments in areas of strong dynamics.