Fluctuations of High-Frequency Acoustic Pulses in Three Shallow-Water Experiments PDF Download
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Languages : en
Pages : 0
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High-frequency acoustic propagation and scattering experiments were conducted near Panama City, Florida, in August of 1991 and 1993, and in Eckernforde Bay, Germany in May 1993. Environmental measurements were made in conjunction with acoustic measurements. The water depth at all sites was approximately 30 m. Sources and receiver arrays were mounted 6 to 8 m from the bottom and were separated by about 80 m. Data were obtained from 20 to 180 kHz. Means, standard deviations, and coefficients of variation of 100 to 150 direct path pulses for each frequency characterize two scales of temporal variability in the data. The short term variability with a period of several seconds was attributed to wind waves while the larger scale changes with a period of several minutes were related to internal waves. The amplitude of the fluctuations depended on a combination of factors including the depth and slope of the thermocline, turbulence from internal waves, wind waves, tides, and current interactions, and whether or not multipath arrivals interacted at the receiver array. Spatial variability was noted among several closely spaced hydrophones. Differences among frequencies depended on environmental factors that were changing with time of day when data were collected, as well as wavelength and beam pattern effects.
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Languages : en
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Book Description
High-frequency acoustic propagation and scattering experiments were conducted near Panama City, Florida, in August of 1991 and 1993, and in Eckernforde Bay, Germany in May 1993. Environmental measurements were made in conjunction with acoustic measurements. The water depth at all sites was approximately 30 m. Sources and receiver arrays were mounted 6 to 8 m from the bottom and were separated by about 80 m. Data were obtained from 20 to 180 kHz. Means, standard deviations, and coefficients of variation of 100 to 150 direct path pulses for each frequency characterize two scales of temporal variability in the data. The short term variability with a period of several seconds was attributed to wind waves while the larger scale changes with a period of several minutes were related to internal waves. The amplitude of the fluctuations depended on a combination of factors including the depth and slope of the thermocline, turbulence from internal waves, wind waves, tides, and current interactions, and whether or not multipath arrivals interacted at the receiver array. Spatial variability was noted among several closely spaced hydrophones. Differences among frequencies depended on environmental factors that were changing with time of day when data were collected, as well as wavelength and beam pattern effects.
Author: D. E. Weston
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Languages : en
Pages : 24
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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).
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Category : Music
Languages : en
Pages : 764
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Author: Paul C. Etter
Publisher: CRC Press
ISBN: 1351831984
Category : Technology & Engineering
Languages : en
Pages : 557
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Underwater Acoustic Modeling and Simulation, Fourth Edition continues to provide the most authoritative overview of currently available propagation, noise, reverberation, and sonar-performance models. This fourth edition of a bestseller discusses the fundamental processes involved in simulating the performance of underwater acoustic systems and emphasizes the importance of applying the proper modeling resources to simulate the behavior of sound in virtual ocean environments. New to the Fourth Edition Extensive new material that addresses recent advances in inverse techniques and marine-mammal protection Problem sets in each chapter Updated and expanded inventories of available models Designed for readers with an understanding of underwater acoustics but who are unfamiliar with the various aspects of modeling, the book includes sufficient mathematical derivations to demonstrate model formulations and provides guidelines for selecting and using the models. Examples of each type of model illustrate model formulations, model assumptions, and algorithm efficiency. Simulation case studies are also included to demonstrate practical applications. Providing a thorough source of information on modeling resources, this book examines the translation of our physical understanding of sound in the sea into mathematical models that simulate acoustic propagation, noise, and reverberation in the ocean. The text shows how these models are used to predict and diagnose the performance of complex sonar systems operating in the undersea environment.
Author: Boris Katsnelson
Publisher: Springer Science & Business Media
ISBN: 1441997776
Category : Science
Languages : en
Pages : 549
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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: Renhe Zhang
Publisher:
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Category : Underwater acoustics
Languages : en
Pages : 660
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Category : Mechanics, Applied
Languages : en
Pages : 686
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Author: Robert J. Urick
Publisher:
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Category : Sound
Languages : en
Pages : 268
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Category : Aeronautics
Languages : en
Pages : 704
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Category : Science
Languages : en
Pages : 212
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