Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 20 for “"Sound speed profile"”.
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A tomographic ocean sound speed profile from a long veritcal acoustic array
An average sound speed profile over a 1000 km section of the northeast Pacific ocean is obtained using Ocean Acoustic Tomography, from data acquired during the 1987 SVLA experiment on a long (900 m) 120 hydrophone vertical acoustic array. In particular, we pulse compress the received signal with a …
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A matched field processing approach to long range acoustic navigation
… The system uses a ray tracing model of sound propagation in a horizontally stratified ocean to associate each multipath arrival with a particular ray path through the ocean. This ray path identification allows an inversion for both vehicle position and sound speed profile parameters. …
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A modal/WKB inversion method for determining sound speed profiles in the ocean and ocean bottom
Two approaches to determining the ocean sound speed profile using measured acoustic modal eigenvalues are examined. Both methods use measured eigenvalues and mode dependent assumed values of the WKB phase integral as input data and use the WKB phase integral as a starting point for relating the …
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A modal analysis of acoustic propagation in the changing Arctic environment
… look at acoustic propagation through double duct sound speed profiles in the Arctic. While the traditional Arctic sound speed profile has a single surface duct, some portions of the Arctic have a sound speed profile which includes a second, lower duct. These double duct systems are seen through …
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Theoretical and numerical studies of wave propagation and scattering in inhomogeneous media
… medium with the linear refractive index profile is obtained. The technique is extended to treat the three-dimensional and range-dependent media with or without turning points. Two analytical expressions of the Green's functions are also obtained for such media. For a line source in the …
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A numerical method for solving for normal modes with impedance bottom
… given the depth of source and receiver, the sound speed profile of the water, the frequency of the source, and the impedance and sound speed in the bottom. The program does this by computing the sum of normal modes for a specified set of boundary conditions. At the surface perfect pressure …
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SOFAR signal shaping : influence of topography and relative source depth
… depth of the source relative to the axis of the sound channel is investigated. Eight shot signals from five different sites near Cape Town were received at three widely spaced hydrophones at Ascension over a number of 4.4 Megametre lines. These signals show the effects of (1) sources at different …
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Efficient inversion methods in underwater acoustics
… and implemented for source localization and sound speed and bottom depth estimation using sound propagation in the ocean. The proposed inversion techniques are based on the linearization of the generally non-linear inverse problem of parameter estimation in underwater acoustics. These …
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Geoacoustic inversion in laterally varying shallow-water experiments using high-resolution wavenumber estimation
Sound propagation in shallow water is highly dependent on the interaction of the sound field with the bottom. In order to fully understand this problem, it is necessary to obtain reliable estimates of bottom geoacoustic properties that can be used in acoustic propagation codes. In this thesis, …
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An inverse method for obtaining the attenuation profile and small variations in the sound speed and density profiles of the ocean bottom
… have a direct effect on the propagation of sound in the ocean. In the frequency range of interest (50 - 500 Hz) the sediment can be modelled as a fluid. Assuming horizontal stratification of the ocean bottom, the acoustic parameters of interest are the compressional wave speed, the …
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Ambient acoustics as indicator of environmental change in the Beaufort Sea: experiments & methods for analysis
… changes are reflected in its underwater ambient soundscape as its origin and propagation are primarily dependent on properties of the ice cover and water column. The first component of this work examines the effect on ambient noise characteristics due to changes to the Beaufort Sea sound speed …
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Ambient Acoustics as Indicator of Environmental Change in the Beaufort Sea: Experiments & Methods for Analysis
… changes are reflected in its underwater ambient soundscape as its origin and propagation are primarily dependent on properties of the ice cover and water column. The first component of this work examines the effect on ambient noise characteristics due to changes to the Beaufort Sea sound speed …
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Inverse methods for sound speed estimation in the ocean
… and computational approaches for estimating sound-speed in the ocean under different conditions. The first part of the dissertation discusses a fast approach for solving the inverse problem of estimating sediment sound-speed based on the Deift-Trubowitz trace formula. Under certain …
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A Virtual Ocean framework for environmentally adaptive, embedded acoustic navigation on autonomous underwater vehicles
… underwater navigation employ a deterministic sound speed to convert recorded travel time into range. In acoustically complex propagation environments, however, accurate navigation is predicated on how the sound speed structure affects propagation. The Arctic’s Beaufort Gyre provides an …
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Understanding and utilizing waveguide invariant range-frequency striations in ocean acoustic waveguides
… the acoustic properties of the seafloor and the sound speed profile (SSP), which limits their applicability. The range-frequency waveguide invariant describes striations that often appear in plots of acoustic intensity versus range and frequency. These range-frequency striations have properties …
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A Virtual Ocean framework for environmentally adaptive, embedded acoustic navigation on autonomous underwater vehicles
… underwater navigation employ a deterministic sound speed to convert recorded travel time into range. In acoustically complex propaganda environments, however, accurate navigation is predicated on how the sound speed structure affects propagation. The Arctic's Beaufort Gyre provides an …
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Understanding and utilizing waveguide invariant range-frequency striations in ocean acoustic waveguides
… the acoustic properties of the seafloor and the sound speed profile (SSP), which limits their applicability. The range-frequency waveguide invariant describes striations that often appear in plots of acoustic intensity versus range and frequency. These range-frequency striations have properties …
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Geoacoustic inversion in laterally varying shallow-water environments using high-resolution wavenumber estimation
Sound propagation in shallow water is highly dependent on the interaction of the sound field with the bottom. In order to fully understand this problem, it is necessary to obtain reliable estimates of bottom geoacoustic properties that can be used in acoustic propagation codes. In this thesis, …
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An experimental study of air entrainment by breaking waves
… is developed. Simultaneous measurements of the sound-speed (and thus the void-fraction) at several depths are conducted during two field experiments. Time-series of sound-speed and attenuation show dramatic fluctuations over time periods on the order of minutes or less. These are attributed to …
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Underwater sound propagation and acoustic communication in a time-varying shallow estuarine environment
… which can significantly influence the underwater sound propagation and moreover, underwater acoustic communications. In order to perform reliably and effectively in such complex time-varying shallow-water ocean environments, next-generation underwater acoustic communication systems need an all new …