High-Frequency Seafloor Acoustics

High-Frequency Seafloor Acoustics

Author: Darrell Jackson

Publisher: Springer Science & Business Media

Published: 2007-08-02

Total Pages: 634

ISBN-13: 0387369457

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This book is a research monograph on high-Frequency Seafloor Acoustics. It is the first book in a new series sponsored by the Office of Naval Research on the latest research in underwater acoustics. It provides a critical evaluation of the data and models pertaining to high-frequency acoustic interaction with the seafloor, which will be of interest to researchers in underwater acoustics and to developers of sonars. Models and data are presented so as to be readily usable, backed up by extensive explanation. Much of the data is new, and the discussion in on two levels: concise descriptions in the main text backed up by extensive technical appendices.


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:

Published: 1982

Total Pages: 14

ISBN-13:

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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).


High-Frequency Acoustic Backscatter from the Sea Surface

High-Frequency Acoustic Backscatter from the Sea Surface

Author: W. I. Roderick

Publisher:

Published: 1984

Total Pages: 39

ISBN-13:

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This document contains the slide presentation entitled 'High-Frequency Acoustic Backscatter From the Sea Surface, ' given at the 107th meeting of the Acoustic Society of America on 8 May 1984 in Norfolk, Virginia. A high resolution scattering experiment was conducted in the shallow waters of the North Atlantic. A narrow beam parametric array, which was rotatable in both azimuth and elevation, was utilized as a broadband high-frequency acoustic projector. Acoustic surface scattering data were obtained at normal incidence and low grazing angles (less than 10 deg) as a function of acoustic transmit frequency and sea state conditions. Meteorologic and oceanographic data were obtained in concert with the acoustic measurements and included wind speed and direction, ocean surface wave spectra and currents, and ocean sound speed. Surface backscattering strength, Doppler spectra (shift and spread), and envelope statistics were some of the measured parameters. It will be shown that the Doppler spectra are approximately Gaussian and the spectral shift could be predicted from Bragg diffraction theory modified by the induced Doppler due to surface currents. The measured Doppler spreads, however, were greater than those predicted by composite roughness theory.


Sounds in the Sea

Sounds in the Sea

Author: Herman Medwin

Publisher: Cambridge University Press

Published: 2005-07-21

Total Pages: 682

ISBN-13: 9780521829502

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Sea Surface Sound

Sea Surface Sound

Author: B.R. Kerman

Publisher: Springer Science & Business Media

Published: 2012-12-06

Total Pages: 629

ISBN-13: 9400930178

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In its relentless pursuit of further knowledge, science tends to compartmentalize. Over the years the pursuit of What might be called geophysical acoustics of the sea-surface has languished. This has occured even through there are well-developed and active research programs in underwater acoustics, ocean hydrodynamics, cloud and precipitation physics, and ice mechanics - to name a few - as well as a history of engineering expertise built on these scientific fields. It remained to create a convergence, a dialogue across disciplines, of mutual benefit. The central theme of the Lerici workshop, perhaps overly simplified, was 'What are the mechanisms causing ambient noise at the upper surface of the ocean?' What could hydrodynamicists contribute to a better understanding of breaking wave dynamics, bubble production, ocean wave dynamics, or near-surface turbulence for the benefit of the underwater acoustics community? What further insights could fluid dynamicists gain by including acoustic measurements in their repertoire of instrumentation? While every attendee will have his or her percep tions of details, it was universally agreed that a valuable step had been taken to bring together two mature disciplines and that significant co-operative studies would undoubtedly follow. The scope of the workshop was enlarged beyond its original intent to also include the question of ice-noise generation. The success of this decision can be seen in high quality of the presentations. the contribution of its disciples in the other workshop discussions and the heightened awareness and interest of we other novices.


Ocean Seismo-Acoustics

Ocean Seismo-Acoustics

Author: T. Akal

Publisher: Springer Science & Business Media

Published: 2013-03-09

Total Pages: 898

ISBN-13: 1461322014

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Seafloor investigation has long been a feature of not only seismology but also of acoustics. Indeed it was acoustics that produced depth sounders, giving us the first capability of producing both global and local maps of the seafloor. Subsequently, better instrumentation and techniques led to a clearer, more quantitative picture of the seabed itself, which stimulated new hypotheses such as seafloor spreading through the availability of more reliable data on sediment thickness over ocean basins and other bottom features. Geologists and geophysicists have used both acoustic and seismic methods to study the seabed by considering the propagation of signals arising from both natural seismic events and man-made impulsive sources. Although significant advances have been made in instrumentation, such as long towed geophysical arrays, ai r guns and ocean bot tom seismometers, the pic ture of the seafloor is still far from complete. Underwater acoustics concerns itself today with the phenomena of propagation and noise at frequencies and ranges that require an understanding of acoustic interaction at both of its boundaries, the sea surface and seafloor, over depths ranging from tens to thousands of meters. Much of the earlier higher frequency (>1 kHz) work included the characterization of the seafloor in regimes of reflection coefficients which were empirically derived from surveys. The results of these studies met with only limited success, confined as they were to those areas where survey data existed and lacking a physical understanding of the processes of reflection and scattering.