Anisotropy of the Wavefront Distortion for Acoustic Pulse Propagation Through Ocean Sound-Speed Fluctuations: A Ray Perspective

Flatté, Stanley M.; Colosi, John A.

doi:10.1109/joe.2008.2006341

Cited by 8 publications

(4 citation statements)

References 27 publications

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“…The prediction of these relatively narrow penetrations of several hundred meters into the shadow zone supports previous observations made during the SLICE89 experiment that internal-wave-induced scattering occurs predominantly along timefronts rather than across them ͑Beron-Vera and Brown, 2004;Flatté and Colosi, 2008;Godin, 2007;Virovlyansky, 2003͒.…”

Section: Axial Shadow-zone Arrivalssupporting

confidence: 87%

The vertical structure of shadow-zone arrivals at long range in the ocean

Uffelen

Worcester

Dzieciuch

et al. 2009

The Journal of the Acoustical Society of America

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Multimegameter-range acoustic data obtained by bottom-mounted receivers show significant acoustic energy penetrating several hundred meters into geometric shadow zones below cusps (caustics) of timefronts computed using climatological databases [B. D. Dushaw et al., IEEE J. Ocean. Eng. 24, 202-214 (1999)]. This penetration is much larger than predicted by diffraction theory. Because these receivers are horizontal arrays, they do not provide information on the vertical structure of the shadow-zone arrivals. Acoustic data from two vertical line array receivers deployed in close proximity in the North Pacific Ocean, together virtually spanning the water column, show the vertical structure of the shadow-zone arrivals for transmissions from broadband 250-Hz sources moored at the sound-channel axis (750 m) and slightly above the surface conjugate depth (3000 m) at ranges of 500 and 1000 km. Comparisons to parabolic equation simulations for sound-speed fields that do not include significant internal-wave variability show that early branches of the measured timefronts consistently penetrate as much as 500-800 m deeper into the water column than predicted. Subsequent parabolic equation simulations incorporating sound-speed fluctuations consistent with the Garrett-Munk internal-wave spectrum at full strength accurately predict the observed energy level to within 3-4-dB rms over the depth range of the shadow-zone arrivals.

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Section: Axial Shadow-zone Arrivalssupporting

confidence: 87%

The vertical structure of shadow-zone arrivals at long range in the ocean

Uffelen

Worcester

Dzieciuch

et al. 2009

The Journal of the Acoustical Society of America

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“…Examples in deep-water problems are the depth broadening of the acoustic finale ͑Worcester et Colosi et al, 1994;Colosi and Flatté, 1996;Worcester et al, 1999͒ and the so-called deep shadow zone arrivals ͑Dushaw et al, 1999;Flatté and Colosi, 2008;Van Uffelen et al, 2009͒. For shallow-water problems, on the other hand, the acoustic arrivals are seen to have significant time spreading ͑Tielburger et al ., 1997;Fredricks et al, 2005͒ which could be due to both random linear internal waves and nonlinear internal solitary waves.…”

Section: Introductionmentioning

confidence: 99%

Statistics of normal mode amplitudes in an ocean with random sound-speed perturbations: Cross-mode coherence and mean intensity

Colosi

Morozov

2009

The Journal of the Acoustical Society of America

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In this paper Creamer's ͓͑1996͒. J. Acoust. Soc. Am. 99, 2825-2838͔ transport equation for the mode amplitude coherence matrix resulting from coupled mode propagation through random fields of internal waves is examined in more detail. It is shown that the mode energy equations are approximately independent of the cross mode coherences, and that cross mode coherences and mode energy can evolve over very similar range scales. The decay of cross mode coherence depends on the relative mode phase randomization caused by coupling and adiabatic effects, each of which can be quantified by the theory. This behavior has a dramatic effect on the acoustic field second moments like mean intensity. Comparing estimates of the coherence matrix and mean intensity from Monte Carlo simulation, and the transport equations, good agreement is demonstrated for a 100-Hz deep-water example.

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“…Using Eqs. (2)-(4) and (13), it can be verified that the solutions of the ray equations satisfy difference equations (14) and (15). In 2D problems, the finite-difference scheme (10), (13)-(15) reduces to the scheme we used in Ref.…”

Section: Finite-difference Schemementioning

confidence: 99%

Tracing Three-Dimensional Acoustic Wavefronts in Inhomogeneous, Moving Media

et al. 2014

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We present a numerical implementation of an alternative formulation of the geometrical, or ray, acoustics, where wavefronts rather than rays are the primary objects. Rays are recovered as a by-product of wavefront tracing. The alternative formulation of the geometrical acoustics is motivated, first, by the observation that wavefronts are often more stable than rays at long-range sound propagation, and, second, by a need for computationally efficient modeling of high-frequency acoustic fields in three-dimensionally inhomogeneous, moving or motionless fluids. Wavefronts are found as a finite-difference solution to a system of partial differential equations, which is equivalent to the eikonal equation and is a direct implementation of the intuitive Huygens' wavefront construction. The finite-difference algorithm is an extension of the approach originally developed in the framework of an open source Madagascar project. Benchmark problems, which admit exact, analytic solutions of the eikonal equation, are formulated and utilized to verify the finite-difference wavefront tracing algorithm. Huygens' wavefront tracing (HWT) is applied to modeling sound propagation in three-dimensionally inhomogeneous ocean and atmosphere.

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Anisotropy of the Wavefront Distortion for Acoustic Pulse Propagation Through Ocean Sound-Speed Fluctuations: A Ray Perspective

Cited by 8 publications

References 27 publications

The vertical structure of shadow-zone arrivals at long range in the ocean

The vertical structure of shadow-zone arrivals at long range in the ocean

Statistics of normal mode amplitudes in an ocean with random sound-speed perturbations: Cross-mode coherence and mean intensity

Tracing Three-Dimensional Acoustic Wavefronts in Inhomogeneous, Moving Media

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