|dc.description.abstract||Sound 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