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dc.contributor.authorHolmes, Jason David
dc.date.accessioned2010-11-19T03:49:47Z
dc.date.available2010-11-19T03:49:47Z
dc.date.issued2007
dc.identifier.urihttp://hdl.handle.net/2144/1376
dc.description.abstractSound propagation in shallow water is characterized by interaction with the oceans surface, volume, and bottom. In many coastal margin regions, including the Eastern U.S. continental shelf and the coastal seas of China, the bottom is composed of a depositional sandy-silty top layer. Previous measurements of narrow and broadband sound transmission at frequencies from 100 Hz to 1 kHz in these regions are consistent with waveguide calculations based on depth and frequency dependent sound speed, attenuation and density profiles. Theoretical predictions for the frequency dependence of attenuation vary from quadratic for the porous media model of M.A. Biot to linear for various competing models. Results from experiments performed under known conditions with sandy bottoms, however, have agreed with attenuation proportional to f1.84, which is slightly less than the theoretical value of f2 [Zhou and Zhang, J. Acoust. Soc. Am. 117, 2494]. This dissertation presents a reexamination of the fundamental considerations in the Biot derivation and leads to a simplification of the theory that can be coupled with site-specific, depth dependent attenuation and sound speed profiles to explain the observed frequency dependence. Long-range sound transmission measurements in a known waveguide can be used to estimate the site-specific sediment attenuation properties, but the costs and time associated with such at-sea experiments using traditional measurement techniques can be prohibitive. Here a new measurement tool consisting of an autonomous underwater vehicle and a small, low noise, towed hydrophone array was developed and used to obtain accurate long-range sound transmission measurements efficiently and cost effectively. To demonstrate this capability and to determine the modal and intrinsic attenuation characteristics, experiments were conducted in a carefully surveyed area in Nantucket Sound. A best-fit comparison between measured results and calculated results, while varying attenuation parameters, revealed the estimated power law exponent to be 1.87 between 220.5 and 1228 Hz. These results demonstrate the utility of this new cost effective and accurate measurement system. The sound transmission results, when compared with calculations based on the modified Biot theory, are shown to explain the observed frequency dependence.en_US
dc.description.sponsorshipNational Defense Science and Engineering Graduate Fellowship through the American Society for Engineering Education, the Office of Naval Research, and the Woods Hole Oceanographic Institution.en_US
dc.language.isoen_USen_US
dc.publisherBoston Universityen_US
dc.rightsAttribution 3.0 Unported*
dc.rights.urihttp://creativecommons.org/licenses/by/3.0/*
dc.subjectAcousticsen_US
dc.subjectOcean sedimenten_US
dc.subjectUnderwater autonomous vehicleen_US
dc.subjectBiot mediumen_US
dc.subjectPower law attenuationen_US
dc.titleINVESTIGATION OF OCEAN ACOUSTICS USING AUTONOMOUS INSTRUMENTATION TO QUANTIFY THE WATER-SEDIMENT BOUNDARY PROPERTIESen_US
dc.typeThesisen_US


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Attribution 3.0 Unported
Except where otherwise noted, this item's license is described as Attribution 3.0 Unported