Oceanographic Component of Joint Acoustics/Oceanography Experiment on the Washington Shelf for Mid-Frequency Sonar Applications
Abstract
Approved for Public ReleaseWe propose a joint ocean-acoustics collaboration, combining interconnected efforts in separate proposalsfrom APL/UW Ocean Physics and APL/UW Acoustics, Scripps MPL Acoustics and from NRLSSC Oceanography, and building upon recent TFO advances in understanding and predicting mid-frequency acoustic propagation in the Washington (WA) coastal ocean. The 2022 TFO field experiment over the WA outer shelf demonstrated the strong impacts of secondary subsurface ducts, internal waves, and coastal ocean dynamics on mid-frequency sound propagation, and posed stringent tests to both regional prediction and assimilation methods in operational ocean models. This expanded joint study targets testing and further development of improvements in measurement and modeling techniques in this region, where subsurface ducts with reliably-high seasonal prevalence impact transmission loss (TL) and are modulated by a wide range of coastal ocean dynamic scales. This study will include coordinated observational components to further advance our joint ocean-acoustic modeling capabilities, focusing on closing identified knowledge deficits and reducing weaknesses in measuring and predicting both the deterministic and probabilistic impacts on mid-frequency sound propagation in this coastal ocean environment, including:#Targeted additions and enhancements of oceanic and acoustic measurement capabilities#Accurate modeling of ocean processes key to seasonal duct formation and evolution#Optimized techniques for model assimilation of observed ducts from real-time data#Mechanisms contributing to the high scintillation of mid-frequency TL observed in 2022#Predicting modulation of TL by O(10) day coastal trapped waves, O(10) hr internal tide-generated nonlinear waves, and up to O(10) min internal waves#Convolved impacts of geoacoustic variability and range-dependent sound speed profiles#Systematic quantification of uncertainty for environmental and acoustic predictions The goals for this APL/UW Ocean Physics component of the collaborative effort are to further improve our understanding ofand capacity to predict coastal ocean sound speed variability, focusing on the physical processes responsible for the acoustic environmental features for which ocean models can have deterministic skill. This includes the formation of mid-frequency subsurface ducts, and the impact of internal waves upon variability of their acoustic effects at seasonal, intermediate (~10 day), and tidal forcing timescales. We will also quantify uncertainty in acoustic transmission from sound speed variability that ocean models can typically only represent stochastically: (1) internal waves at inertial, tidal, and buoyancy frequencies, as well as across intervening spectral cascades, (2) submesoscale dynamics, and (3) thermohaline fine structure. The physics of mid-frequency sound propagation makes these objectives particularly challenging in that small (~1 m/s) sound speed fluctuationsover relatively thin (~10 m) vertical layers persist over long times and lateral distances, with a much larger impact on mid-frequency transmission loss (TL) than their negligibly weak effects on low-frequency propagation might mislead one to expect. With primary goals of quantifying environmental sound speed uncertainty and improving joint ocean-acoustics model predictive skill, our collaborative objectives are to: (1) provide continuous, comprehensive oceanographic measurements to support a ~3-week acoustics field study and guide subsequent model development, and(2) carry out focused acoustic modeling based on validated ocean modeling using the non-assimilating, ROMS-based UW LiveOcean model, the assimilating Navy NCOM models, and subset nonhydrostatic ocean models resolving small scale linear and nonlinear internal wavephenomenal over the
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412781
Entities
People
- Ramsey Harcourt
Organizations
- Office of Naval Research
- United States Navy
- University of Washington