Space-frequency Correlations in Multistatic Acoustic Reverberation Due to a Wind-driven Sea Surface

Space-frequency Correlations in Multistatic Acoustic Reverberation Due to a Wind-driven Sea Surface
Author: R. F. Gragg
Publisher:
Total Pages: 60
Release: 1999
Genre: Seawater
ISBN:

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Analytic methods are used to assess the impact of the two-dimensional (2-D) wave spectrum of a wind-driven sea on multistatic low-frequency surface reverberation. The problem is initially posed with a narrowband source beneath a time-dependent sea surface in an ocean that can have depth dependence and bottom layering. The propagated signal interacts with the slower moving surface waves to produce a narrowband scattered field. The small-waveheight approximation is applied to a deterministic sea surface to express the scattered field in terms of the surface elevation and the Green's function for a perfectly calm sea. Randomness is then incorporated into the surface description, and its impact is formulated for an arbitrarily placed pair of receivers. The three-dimensional (3-D) cross-spectral density (CSD) of the reverberation is reduced to a sum of baseband and sideband terms formulated as multiple mean-sea-surface integrals. The sideband result is identified as an active scattering generalization of the van Cittert-Zernike theorem from partial coherence theory. The focus is then narrowed to shallow deployment in a homogeneous ocean, and stationary-phase estimates are used to produce analytic expressions for the CSD. The zero-Doppler component and Bragg-Doppler sidebands are expressed in terms of the power spectrum of the source, the power spectrum and directionality of the surface waves, and the multistatic source/receiver geometry. Sample sideband calculations are provided to illustrate the results, and system implications are considered.

Ocean Reverberation

Ocean Reverberation
Author: Dale D. Ellis
Publisher: Springer Science & Business Media
Total Pages: 424
Release: 1993
Genre: Technology & Engineering
ISBN:

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This volume comprises over 50 contributions resulting from the Ocean Reverberation Symposium, held 25-29 May 1992 in La Spezia, Italy. The contributions are presented in eight sections: Scattering Mechanisms, High Frequency Measurements and Mechanisms, Reverberation Modelling, ARSRP Mid-Atlantic Ridge Experiment, Low Frequency Measurements, Volume Scattering, Signal Processing Issues and Applications.

Acoustic Reverberation at the Sea Surface: Surface and Sublayer Spectra Vis-a-Vis Scattering and Reflection

Acoustic Reverberation at the Sea Surface: Surface and Sublayer Spectra Vis-a-Vis Scattering and Reflection
Author: John J. Martin
Publisher:
Total Pages: 38
Release: 1968
Genre:
ISBN:

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The paper combines previously developed theories of surface and volume scattering and reflection with published and previously unpublished acoustic reverberation data to develop a composite theory for reverberation strength as a function of acoustic frequency, incidence or grazing angle, and sea-surface wind speed. In passing, spectra of sea-surface roughness and of the surface sublayer turbulence are developed, these spectra being consonant with theoretical and experimental estimates. (Author).

Doppler Spectra of Sea-Surface Backscatter at High Acoustic Frequencies

Doppler Spectra of Sea-Surface Backscatter at High Acoustic Frequencies
Author: W. L. Konrad
Publisher:
Total Pages: 14
Release: 1982
Genre:
ISBN:

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The initial transfer of energy from atmospheric wind to the ocean surface, which would be a significant factor in ambient noise, may occur via the so-called Cat's Paw phenomena. To study this effect, an experiment was conducted at Seneca Lake for a moderately disturbed (no whitecaps) air-water interface. Doppler spectrum measurements of high-frequency acoustic waves backscattered from the wind-driven water surface indicate the presence of small-scale roughness that is convected downward by surface drift. For a slightly rippled surface, there is a sharp resonant peak corresponding to a convection velocity of approximately 0.4 m/s which is nearly independent of wind speed. The spectrum is broadened by phase modulation due to the orbital motion of large-scale gravity waves but remains skewed in the downwind direction. (Author).

Frequency Spreading in Underwater Acoustic Signal Transmission

Frequency Spreading in Underwater Acoustic Signal Transmission
Author: Henti Tung
Publisher:
Total Pages: 211
Release: 1980
Genre: Doppler effect
ISBN:

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The scattering of acoustic waves from a randomly varying wind-driven water surface is known to introduce both time and frequency spreading of the received signal. The frequency spreading is thought to be related to surface statistics and water wave motion. Therefore, knowledge of this relation leads to the possibility of predicting surface statistics by analysis of the received acoustic signal. One important feature of the frequency spreading function is that the Doppler sidebands are not equal in magnitude on both sides of the carrier. Unequal sidebands are predicted if the acoustic source and receiver are not located at the same depths below the water surface and if the direction of the surface wave motion is not perpendicular to the vertical plane containing both the source and the receiver. Experimental results from a model tank operated under various wind conditions have verified the existence of unequal Doppler sidebands under these conditions. However, strong asymmetries in sidebands were also observed under conditions under which the previous theory would have predicted no asymmetries at all. For example, strong asymmetries have been observed in the crosswind direction. This research is to explain the asymmetries not predicted in previous theory but discovered under laboratory operations, and to predict other asymmetries not yet found in either the experimental or the theoretical phase.

Springer Handbook of Acoustics

Springer Handbook of Acoustics
Author: Thomas Rossing
Publisher: Springer Science & Business Media
Total Pages: 1179
Release: 2007-06-21
Genre: Science
ISBN: 0387304460

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This is an unparalleled modern handbook reflecting the richly interdisciplinary nature of acoustics edited by an acknowledged master in the field. The handbook reviews the most important areas of the subject, with emphasis on current research. The authors of the various chapters are all experts in their fields. Each chapter is richly illustrated with figures and tables. The latest research and applications are incorporated throughout, including computer recognition and synthesis of speech, physiological acoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. An accompanying CD-ROM contains audio and video files.

Applied Underwater Acoustics

Applied Underwater Acoustics
Author: Thomas Neighbors
Publisher: Elsevier
Total Pages: 982
Release: 2017-01-19
Genre: Science
ISBN: 0128112476

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Applied Underwater Acoustics meets the needs of scientists and engineers working in underwater acoustics and graduate students solving problems in, and preparing theses on, topics in underwater acoustics. The book is structured to provide the basis for rapidly assimilating the essential underwater acoustic knowledge base for practical application to daily research and analysis. Each chapter of the book is self-supporting and focuses on a single topic and its relation to underwater acoustics. The chapters start with a brief description of the topic’s physical background, necessary definitions, and a short description of the applications, along with a roadmap to the chapter. The subtopics covered within individual subchapters include most frequently used equations that describe the topic. Equations are not derived, rather, assumptions behind equations and limitations on the applications of each equation are emphasized. Figures, tables, and illustrations related to the sub-topic are presented in an easy-to-use manner, and examples on the use of the equations, including appropriate figures and tables are also included. Provides a complete and up-to-date treatment of all major subjects of underwater acoustics Presents chapters written by recognized experts in their individual field Covers the fundamental knowledge scientists and engineers need to solve problems in underwater acoustics Illuminates, in shorter sub-chapters, the modern applications of underwater acoustics that are described in worked examples Demands no prior knowledge of underwater acoustics, and the physical principles and mathematics are designed to be readily understood by scientists, engineers, and graduate students of underwater acoustics Includes a comprehensive list of literature references for each chapter

Adaptive Methods in Underwater Acoustics

Adaptive Methods in Underwater Acoustics
Author: H.G. Urban
Publisher: Springer Science & Business Media
Total Pages: 763
Release: 2012-12-06
Genre: Science
ISBN: 9400953615

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The NATO Advanced Study Institute on Adaptive Methods in Underwater Acoustics was held on 30 July - 10 August 1984 in LLineburg, Germany. The Institute was primarily concerned with signal processing for underwater appl ica tions. The majority of the presentations, when taken together, yield a definite picture of the present status of understanding of adaptive and high resolution processing, setting out the progress achieved over the past four years together with the major problem areas remaining. Major effort was made to obtain a commensurate contribution of tutorial and advanced research papers. It is my hope that the material in this volume may be equally well suited for students getting an introduction to some of the basic problems in underwater signal processing and for the professionals who may obtain an up-to-date overview of the present state of the art. This might be especially useful in view of the controversy and lack of adequate interrelationships which have marked this rapidly expanding field in the past. Practical reinforcement of this picture is provided by the material concerning digital and optical processing technology, giving some guidance to achievable adaptive and high resolution techniques with current processing devices. The formal programme was extended and detailed by a series of six evening work shops on specific topics, during which informal discussions took place among the participants. Summaries of these workshops are also included in these Proceedings.

Underwater Acoustic Data Processing

Underwater Acoustic Data Processing
Author: Y. T. Chan
Publisher: Springer Science & Business Media
Total Pages: 642
Release: 2012-12-06
Genre: Science
ISBN: 9400922892

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This book contains the papers that were accepted for presentation at the 1988 NATO Advanced Study Institute on Underwater Acoustic Data Processing, held at the Royal Military College of Canada from 18 to 29 July, 1988. Approximately 110 participants from various NATO countries were in attendance during this two week period. Their research interests range from underwater acoustics to signal processing and computer science; some are renowned scientists and some are recent Ph.D. graduates. The purpose of the ASI was to provide an authoritative summing up of the various research activities related to sonar technology. The exposition on each subject began with one or two tutorials prepared by invited lecturers, followed by research papers which provided indications of the state of development in that specific area. I have broadly classified the papers into three sections under the titles of I. Propagation and Noise, II. Signal Processing and III. Post Processing. The reader will find in Section I papers on low frequency acoustic sources and effects of the medium on underwater acoustic propagation. Problems such as coherence loss due to boundary interaction, wavefront distortion and multipath transmission were addressed. Besides the medium, corrupting noise sources also have a strong influence on the performance of a sonar system and several researchers described methods of modeling these sources.