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May 1983

Volume 73, Issue S1, pp. S1-S106

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back to top Session F. Underwater Acoustics II: Stochastic Ocean II
Invited Papers
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Review of the path‐integral theory of ocean acoustic fluctuations (A)

Stanley M. Flatté

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S12-S12 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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The path‐integral theory of ocean acoustic fluctuations was systematically introduced in a book, Sound transmission through a fluctuating ocean, by S. M. Flatté, R. Dashen, W. H. Munk, K. M. Watson, and F. Zachariasen (Cambridge U. P., Cambridge, 1979). The theory establishes three regions of fluctuation behavior for acoustic fluctuations along a single deterministic ray caused by internal waves: unsaturated, partially saturated, and fully saturated. Emphasis in this talk will be placed on the saturated regions. A review of progress in comparison of the theory with experiment will be given. Discussion will include results involving second moments (the coherence function of space and time separations, and appropriate Fourier transforms thereof), fourth moments (the scintillation index and spectra of intensity), higher moments (corrections to Rayleigh statistics for the intensity p.d.f.), as well as spectra of phase and log intensity. [Work supported by ONR, Code 425UA.]
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Transport of acoustic radiation along curved rays (A)

F. D. Tappert

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S12-S12 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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A distinguishing feature of sound propagation in the ocean is the existence of the deep sound channel. In consequence ray paths are curved, multipath propagation is prevalent, and caustics abound. This causes severe difficulties in the theory of stochastic wave propagation that have not been fully resolved even on the level of second‐order statistics. We shall discuss two approaches to this problem based on radiation transport theory. The first uses ray coordinates to reformulate the wave equation yielding a parabolic equation valid near a single specified ray. After applying a statistical closure (weak Markov) approximation, we obtain a radiation transport equation along a curved ray. It is shown that when the strong Markov approximation is additionally applied, then this equation may be solved analytically and the results of Flatte et al. are recovered. In other limiting cases, our equation yields different results. The second approach begins with a derivation of a general multipath radiation transport equation. When this equation is expanded near a single specified ray, we obtain results comparable to the first approach but with a shift in the position of the mean ray. Thus the mean intensity on a single arrival is not equal to the unperturbed intensity, as predicted by Flatte et al. In addition, this approach allows calculation of the mean intensity and coherence at a caustic insofar as stochastic effects dominate diffraction.
Contributed Papers
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A generalized stochastic propagation channel characterization (A)

Stanley L. Adams and Fred D. Tappert

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S12-S12 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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Recent work by the authors has led to an elegant generalized propagation channel characterization. The underwater propagation channel is treated as a transformation of space‐time images into space‐time images. Propagation of three‐dimensional space‐time images through random media leads to eight variables, each with independent spreads (or coherencies) in a second‐order moment characterization. From this point of view, generalized system input‐output equations are developed and generalized ambiguity functions are defined. Examples are drawn from several disciplines to qualitatively demonstrate the characterization.
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Acoustic field probability density functions for the canonical sound channel (A)

Susan M. Bates and Bruce J. Bates

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S12-S13 (1983); (2 pages)

Online Publication Date: 12 Aug 2005

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The canonical deep ocean sound channel is parametrized by the sound‐speed minimum, buoyancy frequency scale, and adiabatic fractional sound‐speed gradient. Variations in the sound‐speed parameters depend on spatial and temporal variations in temperature and salinity. These variations are described by probability density functions. The sound channel near the sound‐speed minimum is approximated by a Hirsch sound‐speed profile, and the low‐frequency acoustic field is derived. Analytic field density functions for received frequency, intensity, wave vector, and arrival time are derived by the application of the transformation of random variables, assuming the sound‐speed parameters are uncorrelated Gaussian random variables. The resulting field density functions are non Gaussian. Estimates for the sound‐speed parameters and associated variances are used to evaluate the field density functions.
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Fluctuations of sound propagating vertically through the ocean (A)

Yves Desaubies

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S13-S13 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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We consider internal wave induced fluctuations of sound propagating vertically through the ocean. Expressions are derived for the acoustic phase structure function, variance and spectra. In a number of important oceanic applications sound propagates essentially along the vertical, from the surface (or some depth) to the bottom, as for instance in acoustic depth sounding or tracking of moving objects by bottom mounted hydrophones. The limits imposed by ocean variability on the accuracy of such systems are discussed and are found to be generally small.
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A comparison of the quasi‐Rytov and smoothing methods (A)

Alan R. Wenzel

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S13-S13 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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Two techniques for studying wave propagation in random media, the quasi‐Rytov method and the smoothing method, have been applied to a problem involving radiation by a point source in a one‐dimensional random medium. Each method was used to calculate the mean field, and the results have been compared. It is found that the results are in substantial agreement outside a small region surrounding the source, but that inside this region they disagree. Some technical difficulties which are associated with the smoothing method, and which are related to this discrepancy, are discussed. It is concluded that, although the two methods yield essentially equivalent results (apart from the discrepancy in the near‐source region, which is generally not of practical importance), the quasi‐Rytov method is easier to apply than is the smoothing method. [Work supported by NORDA.]
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Spectral distribution versus propagation path from deep ocean test data (A)

Diana F. McCammon

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S13-S13 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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The distributions of energy across the spectra received during a deep ocean sea test were determined using an unorthodox application of standard statistical analysis. These distributions have been grouped by their principle type of propagation path, e.g., convergence zone or bottom bounce, to enable frequency smearing paths to be identified. This grouping displays clearly the smearing effects of the bottom bounce paths. [Work Supported by NAVSEA, Code 63D‐1.]
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A thermal microstructure measurement system (TMMS) to support high‐frequency acoustic experiments (A)

J. W. Posey, C. Levenson, G. H. Branch, and M. J. Carver

J. Acoust. Soc. Am. Volume 73, Issue S1, pp. S13-S13 (1983); (1 page)

Online Publication Date: 12 Aug 2005

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A microprocessor‐based, high‐resolution thermal microstructure measurement system (TMMS) has been developed and tested which provides near real time at sea measurements of temperature, conductivity, depth, and current direction. The system has been developed in support of the Naval Ocean Research and Development Activity High‐Frequency Acoustic Program [cf. J. W. Posey and C. Levenson, J. Acoust. Soc. Am. Suppl. 1 72, S60 (1982)]. Spatial correlations of temperature and conductivity fluctuations obtainable from TMMS measurements are required for the prediction of fluctuations of high‐frequency acoustic signals. The array consists of a cross braced 2.3×2.3 m frame designed to orient itself normal to existing currents with 15‐cm fixed sensor positioning bars protruding from the cross bars. Twelve matched thermistors, two conductivity probes, and a recording inclinometer are mounted on the frame. A compass and pressure transducer are contained in an electronics package suspended below the array. The array is deployed on a taut mooring below a subsurface float which effectively decouples it from surface perturbations. Data are serially digitized in the electronics package, transmitted on four conductor kevlar cables to a surface buoy and then transmitted via a VHF‐FM radio link to a shipboard control console. Digitally available data are selectively displayed on a printer/plotter. Planned upgrading includes more rugged thermistors with closer tolerances and a digital inclinometer system. [Work supported by NORDA.]
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