TECHNOLOGY AREA(S): Battlespace
OBJECTIVE: Replace the empirical Naval Oceanographic High Frequency Bottom Loss (HFBL) curves with new parameterization for the seabed that includes an improved basis in physics.
DESCRIPTION: The High Frequency Bottom Loss (HFBL) database is generated and managed by the Naval Oceanographic Office (NAVOCEANO). The HFBL is based on a series of nine curves derived by the Marine Geological Survey (MGS) that describe acoustic bottom loss for frequencies ranging between 1.5 “ 4 kHz. HFBL database entries for a given geographic location of the seafloor are determined by the curve, that when used as the input parameters for a model, minimizes the difference between modeled and measured transmission loss (TL). To refine the match between model and measurements for inclusion in the database, curves are interpolated to the nearest 1/10th. This inverse process is carried out independently at each of the 1/3 octave frequencies over the HFBL range. Although the process for generating HFBL data is well established, very high variability in the derived curves from area surveys has been noted. The variability is most prominent in the higher frequency bands and has not been shown to correlate with bottom sediment type. In addition to sediment type, recent work indicates that roughness at the seafloor and sub-bottom interfaces also contribute to bottom loss but are not accounted for in generating the MGS curves. The Navy thus seeks an alternative parameterization of the seafloor to represent BL for frequencies between 1 “ 10 kHz and that accounts for the acoustic properties, layering, and interface scattering of the seabed. The parameterization should also consider variability of sediments and sub-bottom structure as it related to TL variability for both forward and inverse problems.
Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by DoD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Security Service (DSS). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this project as set forth by DSS and ONR in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advanced phases of this contract.
PHASE I: Define and develop concepts to determine feasibility for new parameterization for the seabed to replace the HFBL model that is based on MGS bottom loss curves. Identify the physical properties of the seabed and physical phenomena and perform sensitivity studies to determine relative contributions affecting bottom loss and transmission loss. Identify relevant databases from which parameters can be obtained and/or describe measurements required to obtain them either directly or by inference. Demonstrate utility of new parameterization/model as input to TL models for comparison with predictions based on HFBL.
PHASE II: Based upon the Phase I effort, further validate the proposed parameterization with data representing a variety of different environments. Identify relevant data sets and/or refine the measurement plan developed in Phase I to collect data. Develop a methodology for inverting measured TL data to infer the required parameters for the proposed replacement to the HFBL database. Document the mathematical development of the physics underlying the new parameterization in technical reports. Document and provide algorithms for the inversion process. Extend the sensitivity studies in Phase I to include the effects of spatial variability in parameters on BL and modeled TL. Further extend to include temporal effects that may be relevant at daily and/or seasonal time scales. Develop a scheme for including spatial and temporal variability of parameters for the replacement of the HFBL model. Document the proposed scheme in reports including any algorithms developed.
PHASE III: A successful development will result in the total replacement of the current HFBL model used by NAVOCEANO. Validation and verification of the HFBL replacement will be carried out by the Oceanography and Atmospheric Master Library (OAML) process. Phase III may require security clearance for the contracted team. Private Sector Commercial Potential: The specific application would have primary application in the military. There is some potential for the technology to spin off to scientific and geotechnical applications that require knowledge of the seafloor tailored to their applications.
REFERENCES: 1. P.C. Etter, Underwater Acoustic Modeling and Simulation, 4th Edition, (CRC Press, Boca Raton, FL 2013).2. R.P. Hodges, Underwater Acoustics: Analysis, Design and Performance of Sonar, (J. Wiley & Sons, Chichester, U.K. 2010).3. J. George, D.W. Harvey, A Lowrie, and L.S. Conner, Environmental factors that contribute to high frequency bottom loss variability, J. Acoust. Soc. Am., Vol. 138, pp. 1897 (2015).4. J. Yang, D.R. Jackson, and D. Tang, Mid-frequency geoacoustic inversion using bottom loss data from the Shallow Water 2006 Experiment, J. Acoust. Soc. Am, Vol. 131, pp. 1711 (2012). -
KEYWORDS: Acoustic Propagation; Transmission Loss; Geoacoustic Inversion; Bottom Loss; High-frequency Acoustics; Seabed Characterization
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