Acoustic Fluctuations in Shallow Water Due to Nonlinear Internal Waves PDF Download
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Author: Georges Albert Dossot
Publisher:
ISBN:
Category : Nonlinear acoustics
Languages : en
Pages : 394
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Author: Georges Albert Dossot
Publisher:
ISBN:
Category : Nonlinear acoustics
Languages : en
Pages : 394
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Book Description
Author: Jason Derek Sagers
Publisher:
ISBN:
Category :
Languages : en
Pages : 430
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Book Description
Many problems in shallow water acoustics require accurate predictions of the acoustic field in space and time. The accuracy of the predicted acoustic field depends heavily on the accuracy of the inputs to the propagation model. Oceanographic internal waves are known to introduce considerable temporo-spatial variability to the water column, subsequently affecting the propagation of acoustic waves. As a result, when internal waves are present, errors in model inputs can significantly degrade the accuracy of the predicted acoustic field. Accurate temporo-spatial predictions of the acoustic field in the presence of internal waves therefore depend largely on one's ability to accurately prescribe the water column properties for the acoustic model. This work introduces a data-driven oceanographic model, named the evolutionary propagated thermistor string (EPTS) model, that captures the temporo-spatial evolution of the internal wave field along a fixed track, thereby permitting prediction of temporal fluctuations in the acoustic field. Simultaneously-measured oceanographic and acoustic data from the Office of Naval Research Shallow Water 2006 experiment are utilized in this work. Thermistor measurements, recorded on four oceanographic moorings spaced along the continental shelf, provide the data from which the EPTS model constructs the internal wave field over a 30 km track. The acoustic data were acquired from propagation measurements over a co-located path between a moored source and a vertical line array. Acoustic quantities computed in the model space, such as received level, depth-integrated intensity, and scintillation index are directly compared to measured acoustic quantities to evaluate the fidelity of the oceanographic model. In addition, a strong correlation is observed between the amplitude of the internal wave field and acoustic intensity statistics at a distant receiving array. It is found that the EPTS model possessed sufficient fidelity to permit the prediction of acoustic intensity distributions in the presence of nonlinear internal waves.
Author: D. E. Weston
Publisher:
ISBN:
Category :
Languages : en
Pages : 24
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Book Description
Oscillations of up to 20 dB in level with total duration about 1 1/2 hours have been extensively seen in acoustic propagation experiments, and are due to internal waves. The transmission distances varied from 2 to 23 km in water 35 m deep, with frequency typically about 2 kHz. The internal waves and their acoustic effects were virtually switched on and off through the tidal cycle. This is due to the delicate and varying balance between the vertical density gradient and the shear gradient which together determine the Richardson number. The oceanographic structure was complicated, and included strong horizontal temperature gradients. For 1964 and 1965 experiments in the eastern part of the working area the effects tended to occur near slack water (+ 2 hours relative to local high water) with periods of about 5 min and wavelengths apparently about 50 m. For 1967-1969 experiments in the western part the effects tended to occur near times of maximum flow ( -1 and +5 hours) with periods of about 20 min and wavelengths apparently about 500 m. Measurements from five other indicators of internal waves are included. (Author).
Author: Boris Katsnelson
Publisher: Springer Science & Business Media
ISBN: 1441997776
Category : Science
Languages : en
Pages : 549
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Book Description
Shallow water acoustics (SWA), the study of how low and medium frequency sound propagates and scatters on the continental shelves of the worlds oceans, has both technical interest and a large number of practical applications. Technically, shallow water poses an interesting medium for the study of acoustic scattering, inverse theory, and propagation physics in a complicated oceanic waveguide. Practically, shallow water acoustics has interest for geophysical exploration, marine mammal studies, and naval applications. Additionally, one notes the very interdisciplinary nature of shallow water acoustics, including acoustical physics, physical oceanography, marine geology, and marine biology. In this specialized volume the authors, all of whom have extensive at-sea experience in US and Russian research efforts, have tried to summarize the main experimental, theoretical, and computational results in shallow water acoustics, with an emphasis on providing physical insight into the topics presented.
Author: Lei Fu
Publisher:
ISBN:
Category : Internal waves
Languages : en
Pages : 98
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Book Description
This thesis investigates the amplitude fluctuation effects in acoustic scattering due to shallow water internal waves. Theoretically, it uses the adiabatic approximation and perturbation methods to statistically evaluate acoustic transmission fluctuations caused by internal waves in the ocean; it also investigates acoustic mode coupling effect due to internal waves. Numerically, this thesis simulates the shallow water internal wave(IW) field using the Garrett-Munk internal wave spectrum model and then evaluates acoustic transmission in the simulated internal wave field with the Kraken normal mode program. Theoretical calculations are also performed using the theory developed in this thesis. Comparisons are made between theory and numerical calculations. The results presented and discussed in this thesis are related to the following issues: coherent and incoherent intensity fluctuations for adiabatic approximation, acoustic mode coupling due to IW's, transmission loss difference between adiabatic and coupled mode methods, and their dependence on range, IW amplitude and frequency.
Author: Jing Luo
Publisher:
ISBN: 9781369353761
Category : Fluctuations (Physics)
Languages : en
Pages : 65
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Book Description
Fluctuations of low frequency sound propagation in the presence of nonlinear internal waves during the Shallow Water 2006 experiment are analyzed. Acoustic waves and environmental data including on-board ship radar images were collected simultaneously before, during, and after a strong internal solitary wave packet passed through a source-receiver acoustic track. Analysis of the acoustic wave signals shows temporal intensity fluctuations. These fluctuations are affected by the passing internal wave and agrees well with the theory of the horizontal refraction of acoustic wave propagation in shallow water. The intensity focusing and defocusing that occurs in a fixed source-receiver configuration while internal wave packet approaches and passes the acoustic track is addressed in this thesis. ☐ Acoustic ray-mode theory is used to explain the modal evolution of broadband acoustic waves propagating in a shallow water waveguide in the presence of internal waves. Acoustic modal behavior is obtained from the data through modal decomposition algorithms applied to data collected by a vertical line array of hydrophones. ☐ Strong interference patterns are observed in the acoustic data, whose main cause is identified as the horizontal refraction referred to as the horizontal Lloyd mirror effect. To analyze this interference pattern, combined Parabolic Equation model and Vertical-mode horizontal-ray model are utilized. A semi-analytic formula for estimating the horizontal Lloyd mirror effect is developed.
Author: John A. Colosi
Publisher: Cambridge University Press
ISBN: 1316684032
Category : Science
Languages : en
Pages : 443
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Book Description
The ocean is opaque to electromagnetic radiation and transparent to low frequency sound, so acoustical methodologies are an important tool for sensing the undersea world. Stochastic sound-speed fluctuations in the ocean, such as those caused by internal waves, result in a progressive randomisation of acoustic signals as they traverse the ocean environment. This signal randomisation imposes a limit to the effectiveness of ocean acoustic remote sensing, navigation and communication. Sound Propagation through the Stochastic Ocean provides a comprehensive treatment of developments in the field of statistical ocean acoustics over the last 35 years. This will be of fundamental interest to oceanographers, marine biologists, geophysicists, engineers, applied mathematicians, and physicists. Key discoveries in topics such as internal waves, ray chaos, Feynman path integrals, and mode transport theory are addressed with illustrations from ocean observations. The topics are presented at an approachable level for advanced students and seasoned researchers alike.
Author: John A. Colosi
Publisher: Cambridge University Press
ISBN: 1107072344
Category : Mathematics
Languages : en
Pages : 443
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Book Description
In this book, key discoveries in the field of statistical ocean acoustics over the last 35 years are addressed with illustrations from ocean observations.
Author: Boris G. Katsnelson
Publisher: Springer Science & Business Media
ISBN: 9783540426448
Category : Science
Languages : en
Pages : 296
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Book Description
The objective of this book is to present the main theoretical approaches and models in shallow water acoustics as well as different experimental results. The focus is primarily concentrated on physical results describing the sound field in wave length. The authors show dynamic phenomena (tides, internal waves) from the perspective of acoustic influence as well as the scattering of sound over the macroscopic body in shallow water waveguide. The method of acoustic probing can be used by physicists, geophysicists, geologists and oceanographers.
Author: Fred Tudor Erskine
Publisher:
ISBN:
Category : Naval research
Languages : en
Pages : 188
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Book Description
