Observations of upper ocean sound-speed structures in the North Pacific and their effects on long-range acoustic propagation at low and mid-frequencies

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Authors
Colosi, John A.
Rudnick, Daniel L.
Subjects
Advisors
Date of Issue
2016
Date
Publisher
ASA
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Abstract
Three 1000-km long, high resolution conductivity, temperature, depth sections in the North Pacific Ocean obtained by the ship towed vehicle SeaSoar are analyzed to quantify 2005 March/April upper-ocean sound-speed structure and determine the effects on low to mid-frequency transmission loss (TL) through numerical simulation. The observations reveal a variable mixed layer acoustic duct (MLAD) with a mean sonic layer depth of 91-m, and an even higher variability, 80-m-average-thickness transition layer connecting the mixed layer (ML) with the main ther- mocline. The sound-speed structure is hypothesized to be associated with thermohaline processes such as air-sea fluxes, eddies, submesoscale, fronts, internal waves, turbulence, and spice, but the analysis does not isolate these factors. Upper-ocean variability is quantified using observables of layer depth, ML gradient, and sound speed to compute low order moments, probability density functions, horizontal wavenumber spectra, and empirical orthogo- nal function decomposition. Coupled mode acoustic propagation simulations at 400 and 1000 Hz were carried out using the sound-speed observations from the upper 400-m appended to climatology, which reveal propagation phys- ics associated with diffraction, random media effects, and deterministic feature scattering. Statistics of TL reveal important energy transfers between the MLAD and the deep sound channel.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.1121/10.0002174
Series/Report No
Department
Oceanography
Organization
Naval Postgraduate School (U.S.)
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NPS Report Number
Sponsors
This work was supported by the Office of Naval Research (ONR) code 32 Ocean Acoustics section, as well as support from the ONR Task Force Ocean initiative.
Funder
This work was supported by the Office of Naval Research (ONR) code 32 Ocean Acoustics section, as well as support from the ONR Task Force Ocean initiative.
Format
21 p.
Citation
Colosi, John A., and Daniel L. Rudnick. "Observations of upper ocean sound-speed structures in the North Pacific and their effects on long-range acoustic propagation at low and mid-frequencies." The Journal of the Acoustical Society of America 148.4 (2020): 2040-2060.
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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