Ocean Acoustic Tomography (Cambridge Monographs on Mechanics)
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New material has been added throughout for this third edition. New topics covered include: - inter-thermocline lenses and their effect on sound fields - weakly divergent bundles of rays - ocean acoustic tomography - coupled modes - sound scattering by anisotropic volume inhomogeneities with fractal spectra - Voronovich's approach to sound scattering from the rough sea surface. In addition, the list of references has been brought up to date and the latest experimental data have been included. Toon meer Toon minder. Recensie s From the reviews of the third edition: This is a small book with a wide scope and great intensity.
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In summary, this book is for those wishing to use mathematics to gain insight into the underlying physics behind underwater acoustics. Betrokkenen Auteur L. Lysanov Co-auteur Yu. Reviews Schrijf een review. Bindwijze: Paperback.
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Verwacht over 7 weken Levertijd We doen er alles aan om dit artikel op tijd te bezorgen. Verkoop door bol. In winkelwagen Op verlanglijstje. Gratis verzending 30 dagen bedenktijd en gratis retourneren Ophalen bij een bol. Anderen bekeken ook. Leonid M. Brekhovskikh Fundamentals of Ocean Acoustics , For measuring the average temperature of ocean basins, therefore, the acoustic measurement is quite cost effective.
Ebook Ocean Acoustic Tomography Cambridge Monographs On Mechanics
Tomographic measurements also average variability over depth as well, since the ray paths cycle throughout the water column. A "transceiver" is an instrument incorporating both an acoustic source and a receiver. The slight differences in travel time between the reciprocally-traveling signals are used to measure ocean currents, since the reciprocal signals travel with and against the current.
The average of these reciprocal travel times is the measure of temperature, with the small effects from ocean currents entirely removed. Ocean temperatures are inferred from the sum of reciprocal travel times, while the currents are inferred from the difference of reciprocal travel times. In the ocean, large-scale temperature changes can occur over time intervals from minutes internal waves to decades oceanic climate change. Tomography has been employed to measure variability over this wide range of temporal scales and over a wide range of spatial scales. Indeed, tomography has been contemplated as a measurement of ocean climate using transmissions over antipodal distances.
Tomography has come to be a valuable method of ocean observation, exploiting the characteristics of long-range acoustic propagation to obtain synoptic measurements of average ocean temperature or current. One of the earliest applications of tomography in ocean observation occurred in A collaboration between groups at the Scripps Institution of Oceanography and the Woods Hole Oceanographic Institution deployed a six-element tomographic array in the abyssal plain of the Greenland Sea gyre to study deep water formation and the gyre circulation.
Other applications include the measurement of ocean tides, and the estimation of ocean mesoscale dynamics by combining tomography, satellite altimetry, and in situ data with ocean dynamical models. In addition to the decade-long measurements obtained in the North Pacific, acoustic thermometry has been employed to measure temperature changes of the upper layers of the Arctic Ocean basins, which continues to be an area of active interest. Acoustic thermometry was also recently been used to determine changes to global-scale ocean temperatures using data from acoustic pulses sent from one end of the earth to the other.
Acoustic thermometry is an idea to observe the world's ocean basins, and the ocean climate in particular, using trans-basin acoustic transmissions. Prototype measurements of temperature have been made in the North Pacific Basin and across the Arctic Basin. Starting in , John Spiesberger of the Woods Hole Oceanographic Institution, and Ted Birdsall and Kurt Metzger of the University of Michigan developed the use of sound to infer information about the ocean's large-scale temperatures, and in particular to attempt the detection of global warming in the ocean.
These experiments demonstrated that changes in temperature could be measured with an accuracy of about 20 millidegrees. Spiesberger et al. Instead they discovered that other natural climatic fluctuations, such as El Nino, were responsible in part for substanstial fluctuations in temperature that may have masked any slower and smaller trends that may have occurred from global warming. The measurements terminated when agreed-upon environmental protocols ended.
The decade-long deployment of the acoustic source showed that the observations are sustainable on even a modest budget. The transmissions have been verified to provide an accurate measurement of ocean temperature on the acoustic paths, with uncertainties that are far smaller than any other approach to ocean temperature measurement.
The ATOC project was embroiled in issues concerning the effects of acoustics on marine mammals e.
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Public discussion was complicated by technical issues from a variety of disciplines physical oceanography, acoustics, marine mammal biology, etc. Many of the issues concerning acoustics in the ocean and their effects on marine mammals were unknown. Finally, there were a variety of public misconceptions initially, such as a confusion of the definition of sound levels in air vs. If a given number of decibels in water are interpreted as decibels in air, the sound level will seem to be orders of magnitude larger than it really is - at one point the ATOC sound levels were erroneously interpreted as "louder than 10, airplanes".
In fact, the sound powers employed, W, were comparable those made by blue or fin whales, although those whales vocalize at much lower frequencies.
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The ocean carries sound so efficiently that sounds do not have to be that loud to cross ocean basins. Other factors in the controversy were the extensive history of activism where marine mammals are concerned, stemming from the ongoing whaling conflict, and the sympathy that much of the public feels toward marine mammals.
After six years of study the official, formal conclusion from this study was that the ATOC transmissions have "no significant biological impact". Other acoustics activities in the ocean may not be so benign insofar as marine mammals are concerned. Various types of man-made sounds have been studied as potential threats to marine mammals, such as airgun shots for geophysical surveys, or transmissions by the U. Navy for various purposes. The actual threat depends on a variety of factors beyond noise levels: sound frequency, frequency and duration of transmissions, the nature of the acoustic signal e.
In the case of the ATOC, the source was mounted on the bottom about a half mile deep, hence marine mammals, which are bound to the surface, were generally further than a half mile from the source.
Tomographic transmissions consist of long coded signals e. With precise timing such as from GPS, travel times can be measured to a nominal accuracy of 1 millisecond. While these transmissions are audible near the source, beyond a range of several kilometers the signals are usually below ambient noise levels, requiring sophisticated spread-spectrum signal processing techniques to recover them.