Phase II year
2018
(last award dollars: 2023)
Phase II Amount
$3,499,778
We propose development of an improved bottom database suitable for use in the frequency range of 1-10 kHz. Measured transmission loss (TL) and reverberation level (RL) will be jointly processed in building the database. The influence of the rough sea surface, rough seafloor, as well as subbottom heterogeneity will be accounted for during database generation. The rough sea surface will be characterized by wind speed and wind direction, and the seafloor by a layered sediment where each interface is allowed to be rough and each layer allowed to be heterogeneous. A suite of models (e.g., rough surface PE, rough surface transport equation, or rough surface ray tracing, the GABIM model for characterization of bottom backscatter, and reverberation models based on perturbation theory) will be jointly applied to process measured wideband data in order to populate the database. Numerical simulations and field data with companion environmental data (TREX13) will be used to test the procedure, parameterization, and resulting database. The new procedure will then be applied to existing and new NAVOCEANO data sets to check consistency of the data basing results across regions with similar sediment types.
Benefit: The products resulting from this work will be both a new procedure to build bottom databases and ta a greatly improved database for use in tactical decision aids and mission planning tools.
Keywords: Propagation, bottom-loss database, Reverberation, High-Frequency, forward scattering ---------- The existing HFBL (High-Frequency Bottom Loss) database has been recognized to be unsatisfactory due to its lack of physical underpinning and inability to provide consistent performance across frequency and space. The aim of the project is to replace the HFBL database with a geoacoustic model that leads to a smooth transition to the LFBL (Low-Frequency Bottom Loss) model at 1 kHz. To this end, this project has been focusing on analyzing the extensive dataset provided by NAVOCEANO to understand its physical nature. While this project is focused on applications, work so far has shown that the effort touches on almost all aspects of basic ocean acoustics for mid-frequencies (1-10 kHz). Work under this effort will 1) develop and document the software tools that read the NAVO database of measured transmission loss and environment information; set up the acoustic models for particular runs; and do an inversion for geoacoustic parameters. 2) analyze in detail specific subsets of the data where the model/data agreement is good to demonstrate the capability 3) analyze data from the Seabed Characterization Experiments in the New England Shelf area to demonstrate the processes in a new area. Based on work to date, we expect to show that different 'objective functions' (matching TL in third-octave bands, time-series matching, etc.) will work best for different areas. For instance, near-field and/or deep-water measurements are more amenable to matching the full time-series. Further, in deep water complicated sub-bottom layering will be present only in some areas and require particular techniques. The work will address these issues and make recommendations for a general process.
Benefit: The products resulting from this work will be both a new procedure to build bottom databases and ta a greatly improved database for use in tactical decision aids and mission planning tools. Bottom-loss databases are also of importance in commercial and/or civilian applications. For instance, they supply critical information for modeling acoustic communication networks. They are also used in studies of effects of sound on the marine environment and for tracking marine mammals.
Keywords: Reverberation, Bottom-Loss, forward scattering, Propagation, high frequency
