Evidence of Doppler-shifted Bragg scattering in the vertical plane by ocean surface waves

A set of narrowband tones (280, 370, 535, and 695Hz) were transmitted by an acoustic source mounted on the ocean floor in 10m deep water and received by a 64-element hydrophone line array lying on the ocean bottom 1.25km away. Beamformer output in the vertical plane for the received acoustic tones s...

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Bibliographic Details
Published in:The Journal of the Acoustical Society of America 2012-03, Vol.131 (3), p.2011-2022
Main Authors: Lynch, Stephen D., D'Spain, Gerald L.
Format: Article
Language:English
Subjects:
Acoustics
Exact sciences and technology
Fundamental areas of phenomenology (including applications)
Physics
Underwater sound
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Summary:A set of narrowband tones (280, 370, 535, and 695Hz) were transmitted by an acoustic source mounted on the ocean floor in 10m deep water and received by a 64-element hydrophone line array lying on the ocean bottom 1.25km away. Beamformer output in the vertical plane for the received acoustic tones shows evidence of Doppler-shifted Bragg scattering of the transmitted acoustic signals by the ocean surface waves. The received, scattered signals show dependence on the ocean surface wave frequencies and wavenumber vectors, as well as on acoustic frequencies and acoustic mode wavenumbers. Sidebands in the beamformer output are offset in frequency by amounts corresponding to ocean surface wave frequencies. Deviations in vertical arrival angle from specular reflection agree with those predicted by the Bragg condition through first-order perturbation theory using measured directional surface wave spectra and acoustic modes measured by the horizontal hydrophone array.
ISSN:0001-4966
1520-8524
DOI:10.1121/1.3683247