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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Analysis of temperature variability between Davidson Seamount and Sur Ridge : the tomographic inverse problem /

Neander, David O. January 2002 (has links) (PDF)
Thesis (M.S.)--Naval Postgraduate School, 2002. / Thesis advisor(s): Ching-Sang Chiu, Curtis A. Collins. Includes bibliographical references (p. 55-57). Also available online.

Variational assimilation of acoustic tomography

Liu, Ming, January 1995 (has links)
Thesis (Ph. D.)--Florida State University, 1995. / Typescript. Includes bibliographical references.

Acoustic modeshape inversion using deep water ambient noise measurements

AlMuhanna, Khalid A., January 2008 (has links)
Thesis (M.S.)--George Mason University, 2008. / Vita: p. 69. Thesis director: Kathleen E. Wage. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering. Title from PDF t.p. (viewed Aug. 27, 2008). Includes bibliographical references (p. 67-68). Also issued in print.

A measurement of ocean-bottom slope

Newman, Howard S. January 1900 (has links)
Originally presented as the author's thesis (master's, University of Rhode Island). / Cover title. "27 April 1967." Includes bibliographical references (leaf 54).

Effects of internal waves and turbulent fluctuations on underwater acoustic propagation

Wojcik, Stefanie E. January 2006 (has links)
Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: ray chaos, eikonal equations, turbulence. Includes bibliographical references. (p.98-102).

A two-stage matched-field tomography method for estimation of geoacoustic properties

Corré, Vanessa 16 August 2018 (has links)
Knowledge of the geoacoustic properties of the ocean bottom is essential for accurate modeling of acoustic propagation in shallow-water environments. Estimates of these properties can be obtained through geoacoustic inversion. Among the various inversion methods, the ones based on matched-field processing (MFP) have been increasingly used due to their relatively easy implementation and their good performance. In matched-field inversion (MFI), the objective is to maximize the match between the measured acoustic pressure field and the modeled field calculated for trial sets of geoacoustic parameters characterizing the environment. This thesis investigates the technique of matched-field tomographic inversion, a recent application of MFI that takes advantage of a multiple array-multiple source configuration to estimate range-dependent geoacoustic parameters. A two-stage inversion method based on the ray approach adopted to calculate the modeled pressure fields is developed to increase the efficiency of the estimation. The first stage consists of matching measured and modeled amplitudes of waterborne rays propagating between each source-array pair to estimate the parameters at the seafloor. The second stage consists of matching measured and replica pressure fields corresponding to rays that penetrate the sediment to estimate deeper parameters. In the first stage, the match is quantified using a least-squares function whereas in the second stage the robust pairwise processor is used. Both stages use a simplex genetic algorithm to guide the search over the parameter space. The inversion method is first applied to the two-dimensional (2-D) problem of vertical-slice tomography where four sets (2 sources x 2 vertical line arrays) of multi-tone pressure fields are used to estimate the depth and range variations of geoacoustic parameters. The method is validated via simulation studies that show its good performance in the ideal case where every model parameter except the ones to be estimated are exactly known, and quantify its limitations in non-ideal cases where noise in the data or errors in the array positions are present. The inversion results show that the parameters to which the pressure field is the most sensitive are well estimated for signal-to-noise ratios greater than or equal to 5 dB or for array position uncertainties less than two wavelengths of the source wavelet. The inversion method is then applied to a 3-D environment problem. From the different array configurations studied, it is found that the accuracy of the parameter estimates increases with decreasing propagation range. Finally, the method is applied to experimental data for a vertical-slice configuration. The relatively poor match obtained between the replica and measured data is attributed to the large uncertainty in the array position and the simplistic parameterization of the environment. / Graduate

Three-Dimensional Inversion Technique in Ocean Acoustics Using the Parabolic Equation Method

Unknown Date (has links)
A three-dimensional parabolic equation (PE) and perturbation approach is used to invert for the depth- and range-dependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known range-independent profile and an unknown depth- and range-dependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the range-independent profile, and a scattered field, which is due to the range-dependent perturbation. When the Born approximation is applied to the resulting integral equation, it can be solved for the range-dependent profile using linear inverse theory. Although the method is focused on inverting for the sound speed profile in the bottom, it can also invert for the sound speed profile in the water column. For simplicity, the sound speed profile in the water column was assumed to be known with a margin of error of ± 5 m/s. The range-dependent perturbation is added to the index of refraction squared n2(r), rather than the sound speed profile c(ro). The method is implemented in both Cartesian (x,y,z) and cylindrical (r,q,z) coordinates with the forward propagation of the field in x and r, respectively. Synthetic data are used to demonstrate the validity of the method [1]. Two inversion methods were combined, a Monte Carlo like algorithm, responsible for a starting approximation of the sound speed profile, and a steepest descent method, that fine-tuned the results. In simulations, the inversion algorithm is capable of inverting for the sound speed profile of a flat bottom. It was tested, for three different frequencies (50 Hz, 75 Hz, and 100 Hz), in a Pekeris waveguide, a range-independent layered medium, and a range-dependent medium, with errors in the inverted sound speed profile of less than 3%. Keywords: Three-dimensional parabolic equation method, geoacoustic inversion, range-dependent sound speed profile, linear inversion, Born approximation, Green’s functions. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

Doppler processing of phase encoded underwater acoustic signals

Eldred, Randy Michael. January 1990 (has links) (PDF)
Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 1990. / Thesis Advisor(s): Miller, James H. Second Reader: Tummala, Murali. "September 1990." Description based on title screen as viewed on December 17, 2009. DTIC Identifier(s): Acoustic tomography, inverse problems, Fast Hadamard Transforms, theses. Author(s) subject terms: Acoustic tomography, Fast Hadamard Transform, maximal-length sequences, Doppler processing. Includes bibliographical references (p. 95-96). Also available in print.

A methodology to detect and classify underwater unexploded ordnance in DIDSON sonar images

Unknown Date (has links)
High-resolution sonar systems are primarily used for ocean floor surveys and port security operations but produce images of limited resolution. In turn, a sonar-specific methodology is required to detect and classify underwater unexploded ordnance (UXO) using the low-resolution sonar data. After researching and reviewing numerous approaches the Multiple Aspect-Fixed Range Template Matching (MAFR-TM) algorithm was developed. The MAFR-TM algorithm is specifically designed to detect and classify a target of high characteristic impedance in an environment that contains similar shaped objects of low characteristic impedance. MAFR-TM is tested against a tank and field data set collected by the Sound Metrics Corp. DIDSON US300. This thesis document proves the MAFR-TM can detect, classify, orient, and locate a target in the sector-scan sonar images. This paper focuses on the MAFR-TM algorithm and its results. / by Lisa Nicole Brisson. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

Effects of Internal Waves and Turbulent Fluctuations on Underwater Acoustic Propagation

Wojcik, Stefanie E 09 March 2006 (has links)
A predictive methodology for received signal variation as a function of ocean perturbations is developed using a ray-based analysis of the effects of internal waves and ocean turbulence on long and short range underwater acoustic propagation. In the present formulation the eikonal equations are considered in the form of a second-order, nonlinear ordinary differential equation with harmonic excitation due to an internal wave. The harmonic excitation is taken imperfect, i.e., with a random phase modulation due to Gaussian white noise, accounting for both chaotic and stochastic behavior. Simulated turbulence is represented using the potential theory line vortex approach. Simulations are conducted for long range propagation, 1000km, containing internal wave fields with added deterministic effects and are compared to those fields with non-deterministic properties. These results show that long range acoustic propagation has a very strong dependence on the intensity of deterministic fluctuations. Numerical analysis for short range propagation, 10km, was constructed for sound passage through the following perturbation scenarios: simulated turbulence, an internal wave field, and a field of internal waves and simulated turbulence combined. Investigation over varied initial conditions and perturbation strengths suggests internal wave environments supply the majority of spatial variation and turbulent eddy fields are primarily responsible for delay fluctuation. Spectra of the variations in mean travel velocity reveal internal wave dominance to be dependent on the intensity of the wave.

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