Improving the Physics of Applied Reverberation Models

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OBJECTIVE: Produce higher fidelity acoustic reverberation solutions for complex shallow and deep water environments by incorporating important physical effects into applied Navy models/codes used in mission planning tools, TDAs and school house training. DESCRIPTION: Modeling acoustic propagation and boundary scattering in complex shallow water environments requires numerical modeling. Research level models incorporate high fidelity physics (e.g., surface, bottom and sub-bottom roughness, bottom and volume discrete scatterers) at the cost of slow processing speeds. Current applied codes, that need several orders of magnitude increases in processing speeds relative to research codes, increase speed by both using ray (GRAB/CASS) and energy flux (ASTRAL/ASPM) approximations and incorporating"clutter"as an extra step not based on fundamental scattering physics but on the desired character of the signature at the output of the signal processing algorithms. Recent advances in research modeling hold the promise of adding scattering physics to applied codes with minimal cost in processing speed. PHASE I: Identify treatment of physical phenomena within high fidelity reverberation codes that are mature enough and efficient enough to add to applied codes that use rays or energy flux as the basis of calculation. Identify steps required and/or perform initial integration, of one or more of the physical phenomena identified, into ray and energy flux based codes, demonstrate increased fidelity in those codes and develop processing speed and memory utilization metrics. PHASE II: Complete integration of physical phenomena identified in Phase I into ray and energy flux based codes and perform initial validation and verification studies of the updated codes and document the expanded applications and increased fidelity of the new models. Document the associated mathematical development and implementation in technical reports. Include details on processing speed and memory utilization with and without these increases in fidelity. PHASE III: A successful development will be directly applicable to current Navy applied codes (GRAB/CASS, ASTRAL/ASPM). The increases in fidelity developed in Phase I and II will be integrated into those codes. Validation and verification of new versions of GRAB/CASS and ASTRAL/ASPM will be carried out via the OAML process. Phase III may require security clearance for those involved. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The specific application would have primary application in the military. There is some potential for the technology to spin off to scientific and fisheries applications that involve detection of fish or marine mammals. REFERENCES: 1.H. Weinberg, R. Keenan,"Gaussian ray bundles for modeling high-frequency propagation loss under shallow water conditions,"J. Acoust. Soc. Am, Vol. 100, pp. 1421-1431 (1996). 2. R. Keenan,"An Introduction to GRAB Eigenrays and CASS Reverberation and Signal Excess,"OCEANS 2000 MTS/IEEE Conference Proceedings, Providence, RI, Sept. 11-14, 2000. 3. J. X. Zhou,"The analytical method of angular power spectrum, range and depth structure of echo-reverberation ratio in shallow water sound field,"J. Med. Lab Technol., Vol. 5, pp. 86-99 (1980). 4. C. W. Holland,"Propagation in a waveguide with range-dependent seabed properties,"J. Acoust. Soc. Am, Vol. 128, pp. 2596-2609 (2010).

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