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.
Results
Showing 1 to 20 of 20 for “"Ray Theory"”.
-
Offset vertical seismic profiling : two-dimensional forward modeling with asymptotic ray theory
Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1984.
-
Underwater simulation and mapping using imaging sonar through ray theory and Hilbert maps
… environments. The simulation relies on a ray theory based method and explanations of how this theory follows from first principles under short-wavelegnth assumption are provided. In the second part of this dissertation, the simulator is combined to a continous map algorithm based on …
-
Prediction of the beamformed acoustic ray arrival structure for the 1992 Barents Sea coastal tomography test
… bottom sound source to a vertical hydrophone array was simulated based on three-dimensional ray theory. based on three- dimensional ray theory. Through numerical raytracing, followed by eigenray searches and estimations of ray amplitudes, searches and estimations of ray amplitudes, phases and …
-
Wavefront Healing and Tomographic Resolution of Mantle Plumes
… delay measurements with calculations based on ray theory and show that an anti-correlation between bulk sound speed and S-wave speed could be produced as an artifact. This is caused by different wavefront healing effects between P waves and S waves in thermal plume models. The bulk sound speed …
-
Stochastic acoustic ray tracing with dynamically orthogonal equations
… implementations of the Parabolic Equation, Ray Theory, and Level Sets methods for ocean acoustic computation. We investigate methods for evolving stochastic fields using direct Monte Carlo, Empirical Orthogonal Functions, and adaptive Dynamically Orthogonal (DO) differential equations. As we …
-
APPROXIMATE VS. PURELY NUMERICAL APPROACHES FOR FULL WAVEFORM MODELLING OF GLOBAL EARTH STRUCTURE
… with weak heterogeneity; and, (ii) the full ray theory approach, which should be valid for smooth media. We find that the Born approximation has a very limited domain of validity. It only models accurately surface waveforms with wave periods longer than T»80 s–90 s in existing earth models, …
-
Stochastic acoustic ray tracing with dynamically orthogonal equations
… implementations of the Parabolic Equation, Ray Theory, and Level Sets methods for ocean acoustic computation. We investigate methods for evolving stochastic fields using direct Monte Carlo, Empirical Orthogonal Functions, and adaptive Dynamically Orthogonal (DO) differential equations.
-
A tomographic ocean sound speed profile from a long veritcal acoustic array
… long (900 m) 120 hydrophone vertical acoustic array. In particular, we pulse compress the received signal with a phase-only matched filter. The signal, centered at 80Hz, is phase-modulated by a maximal length sequence. A fast m-sequence cross-correlation algorithm based on the Hadamard transform …
-
A contribution to the jet noise installation problem
… and validated using experimental data. A new 3D ray theory jet propagation method for sources in a steady inhomogeneous moving medium is presented. This method is benched marked using an analytical solution of the Lilley equation. The 3-D method is further enhanced by combing it with realistic …
-
Efficient inversion methods in underwater acoustics
… intensive. For the inversion, select ray paths are taken into account: the direct, first surface bounce, and first bottom bounce. Ray travel time derivatives with respect to parameters that affect path arrival times are obtained analytically. These derivatives and a first order …
-
Surface wave propagation in 3-D anelastic media
… period surface waves. In tomography studies, ray theory breaks down and finite frequency effects become important when the length scale of heterogenities are smaller than seismic wavelength. Finite frequency effects in 3-D earth models are investigated by comparing theoretical predictions of …
-
Imaging Resolution of the 410-km and 660-km Discontinuities
… waves is about 50% of what predicted by ray theory when the topography length scale is in the order of 400 km. The observed arrival anomaly further reduces to 10-20% when the topography length scale reduces to about 200 km. We calculate 2-D boundary sensitivity kernels for direct P waves …
-
Surface wave, internal wave, and source motion effects on matched field processing in a shallow water waveguide
… a shallow water waveguide. We utilize a modified ray theory, based on the work of Tindle, to calculate the acoustic pressure field. This allows us to simply incorporate range dependent environmental conditions as well as to generalize our work to deeper waveguides. In general, the conventional …
-
Seismic Imaging of Earth’s Core-Mantle Boundary using Diffracted Waves
… observations, numerical synthetics, asymptotic theory, and use it as a tool to resolve the fine-scale structure close to the core- mantle boundary. We present seismic observations of rare core-diffracted signals sensitive to the interior of the Hawaiian ULVZ at the highest frequency yet …
-
The acoustics of curved and lined cylindrical ducts with mean flow
… interesting characteristics are explained using ray theory. This analysis is applied to a hard-walled RAE 2129 duct, and frequency-domain solutions are convolved to give a time-domain example of a pulse propagating along this duct. Finally, some numerical work on the nonlinear propagation of a …
-
The Analysis and Prediction of Jet Flow and Jet Noise about Airframe Surfaces
… is found numerically using a newly developed ray tracing method. The variation of the aerodynamics, acoustic source, and far- field acoustic intensity are examined as a large flat plate is moved relative to the nozzle exit. Steady RANS solutions are used to study the aerodynamic changes in the …
-
Ray Tracing Confirms the Optical Properties of the Bovine Lens Are Actively Maintained by the Microcirculation System
… this hypothesis, I have developed a novel laser ray tracing (LRT) system that allows the optical properties of isolated bovine lenses maintained in organ culture to be measured. A fully automated LRT system capable of passing multiple rays at different projection angles through bovine lenses …
-
Interference and resonance of internal gravity waves
… physical insight through the application of ray theory. Thereafter, we proceed to consider smoothly varying stratifications, demonstrating that these resonance and diminution features persist beyond simple models. We conclude by considering the relevance of the results to geophysical …
-
Long-range Propagation, Interaction, and Dissipation of Small-Scale Gravity Waves in the Mesosphere and Lower Thermosphere
… Pasko, </em> 2008] is used in conjunction with ray-theory to investigate the long-range propagation, dissipation and interaction of small-scale gravity waves in the Mesosphere and Lower Thermosphere (MLT) region. The research in this thesis is made up of three distinct studies which build upon …
-
Seismic structure beneath Southeast Asia from adjoint waveform tomography
… tomographic methods are based on seismic ray theory and hence do not fully account for the true physics of wave propagation. Recent computational advances allow us to embrace the full complexity of seismic wave propagation by accurately solving the 3-D seismic wave equation numerically. …