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Real-time Probabilistic Coupled Ocean Physics-Acoustics Forecasting and Data Assimilation for Underwater GPS

Mirabito, C., P.F.J. Lermusiaux, P.J. Haley, Jr., W.H. Ali, E. Dorfman, A. Laferriere, A. Kofford, G. Shepard, M. Goldsmith, K. Heaney, E. Coelho, J. Boyle, J. Murray, L. Freitag, and A. Morozov, 2020. Real-time Probabilistic Coupled Ocean Physics-Acoustics Forecasting and Data Assimilation for Underwater GPS. In: OCEANS '20 IEEE/MTS, 5-30 October 2020, sub-judice.

The POSYDON program aims to develop a Global Positioning System (GPS) for underwater assets. The primary goals of our MIT effort are to: (1) Employ and develop our regional ocean modeling, data assimilation, and uncertainty quantification for the estimation of sound speed variability, coupled oceanographic-acoustic forecasting and inversion relevant to the POINT effort; (2) Apply our theory and schemes for optimal placement, path planning, and persistent ocean sampling with varied assets and acoustic source platforms; and (3) Further quantify the ocean dynamics and variability of the regional areas of interest, utilizing our multi-resolution data-assimilative ocean modeling and process studies.

As part of this program, we completed regional ocean modeling and forecasting for the Middle Atlantic Bight. Our realistic data-assimilative modeling involved real-time forecasting and data-driven simulations and analyses of the sound speed variability. To do so, we built on our experiences, especially on large and collaborative research initiatives. Our methods and software were used and further developed for POINT.

For this project, we also characterized and forecasted the oceanographic variability and uncertainty. Our MIT-MSEAS PE model of the temporal and spatial evolution of physical features and circulations has been validated through extensive measurements, and analysis in many regions. However, due to the uncertain initial and boundary conditions, and sub-grid-scale parameters, the variability of the environmental propagating medium is uncertain. Just as we now utilize probabilities for rain or bad weather on a daily basis, the proposed underwater communication and global positioning system for deep ocean navigation can also utilize and benefit from such information. Real-time integrated oceanographic-acoustic predictions must account for and forecast these uncertainties and their effects on sound propagation and communications.

For this “Precision Ocean Interrogation, Navigation, and Timing (POINT)” effort, we utilized our MIT Multidisciplinary Simulation, Estimation, and Assimilation System (MSEAS) (MSEAS, 2013; Haley et al., 2010, 2015). The MSEAS software is used for fundamental research and for realistic simulations and predictions in varied regions of the world’s ocean, including monitoring, ecosystem prediction and environmental management and, importantly for the present project, real-time oceanographic-acoustic predictions and coupled ocean-acoustic data assimilation. For this exercise, we mainly employed our MIT-MSEAS hydrostatic PE code with a nonlinear free surface, based on second-order structured finite volumes.