Acoustic Ducting, Reflection, Refraction, and Dispersion by Curved Nonlinear Internal Waves in Shallow Water

Lynch, James F.; Lin, Ying‐Tsong; Duda, Timothy F.; Newhall, Arthur E.

doi:10.1109/joe.2009.2038512

Cited by 71 publications

(58 citation statements)

References 24 publications

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“…It can be observed that at the times when internal waves were present, the standard deviation of the 1.5 min localization record also increased. It is known that nonlinear internal waves can distort the coherent structure of the sound field due to mode coupling (Duda and Preisig, 1999) and 3-D sound propagation effects (Lynch et al, 2010). When there is a nonlinear internal wave group in the propagation path, the localization suffers from these propagation effects and the performance can be degraded.…”

Section: Environmental Effectsmentioning

confidence: 99%

Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean

Lin

Newhall

Lynch

2012

The Journal of the Acoustical Society of America

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A variety of localization methods with normal mode theory have been established for localizing low frequency (below a few hundred Hz), broadband signals in a shallow water environment. Gauss-Markov inverse theory is employed in this paper to derive an adaptive normal mode backpropagation approach. Joining with the maximum a posteriori mode filter, this approach is capable of separating signals from noisy data so that the back-propagation will not have significant influence from the noise. Numerical simulations are presented to demonstrate the robustness and accuracy of the approach, along with comparisons to other methods. Applications to real data collected at the edge of the continental shelf off New Jersey, USA are presented, and the effects of water column fluctuations caused by nonlinear internal waves and shelfbreak front variability are discussed.

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Section: Environmental Effectsmentioning

confidence: 99%

Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean

Lin

Newhall

Lynch

2012

The Journal of the Acoustical Society of America

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“…In the following example we place two identical internal waves (with the same amplitude and width as in the examples above) centered at y s = ±300 m. [18,19] and curvature [17] of the duct, since there is (almost) no cylindrical spreading associated with its propagation. Along with ducting of incident mode one, one can also note ducting of a coupled mode two, which is 15-20 dB weaker than the ducting of the initial mode one.…”

Section: A Multiple Wavesmentioning

confidence: 99%

“…Analysis of multiple SAR images, including this example suggests that the angle of the waves cross varies widely from 0 to 90 degrees. Although curvature of the internal wave fronts is commonly observed together with the wave crossings, in this chapter we will study the effects of three-dimensional acoustic propagation through the medium that contains crossing of straight wave trains (acoustical effects caused by the wave curvature are studied in [41,17]). In particular, we are interested in the interaction of the acoustic energy ducted in between waves from one train with crossing wave train.…”

Section: Chapter 6 Crossing Internal Wavesmentioning

confidence: 99%

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Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Shmelev¹

2011

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This thesis describes the physics of fully three-dimensional low frequency acoustic interaction with internal waves, bottom sediment waves and surface swell waves that are often observed in shallow waters and on continental slopes. A simple idealized model of the ocean waveguide is used to analytically study the properties of acoustic normal modes and their perturbations due to waves of each type. The combined approach of a semi-quantitative study based on the geometrical acoustics approximation and on fully three-dimensional coupled mode numerical modeling is used to examine the azimuthal dependence of sound wave horizontal reflection from, transmission through and ducting between straight parallel waves of each type. The impact of the natural crossings of nonlinear internal waves on horizontally ducted sound energy is studied theoretically and modeled numerically using a three-dimensional parabolic equation acoustic propagation code. A realistic sea surface elevation is synthesized from the directional spectrum of long swells and used for three-dimensional numerical modeling of acoustic propagation. As a result, considerable normal mode amplitude scintillations were observed and shown to be strongly dependent on horizontal azimuth, range and mode number. Full field numerical modeling of low frequency sound propagation through large sand waves located on a sloped bottom was performed using the high resolution bathymetry of the mouth of San Francisco Bay. Very strong acoustic ducting is shown to steer acoustic energy beams along the sand wave's curved crests.

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“…Furthermore, the variability of internal waves can significantly alter the acoustic field as they propagate through an area, irregularly displacing the pycnocline. Several studies have been conducted highlighting the common presence of internal waves along the New England shelf (Apel & Jackson, 2002;Colosi, et al, 2001;Jackson, 2004;Lynch, Lin, Duda, Newhall, & Gawarkiewicz, 2009;Tang, et al, 2006).…”

Section: Environmental Variabilitymentioning

confidence: 99%

Environmental analysis and prediction of transmission loss in the region of the New England Shelfbreak

Hornick¹

2009

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A confluence of several coastal oceanographic features creates an acoustically interesting region with high variability along the New England Shelfbreak. Determining the effect of the variability on acoustic propagation is critical for sonar systems. In the Nantucket Shoals area of the Middle Atlantic Bight, two experiments, the New England Shelfbreak Tests (NEST), were conducted in May and June, 2007 and 2008, to study this variability. A comprehensive climatology of the region along with the experimental data provided detailed information about the variability of the water column, particularly the temperature and sound speed fields. Empirical orthogonal function (EOF) analysis of the ocean sound speed field defined a set of perturbations to the background sound speed field for each of the NEST Scanfish surveys.Attenuation due to bottom sediments is the major contributor of transmission loss in the ocean. In shallow water, available propagation paths most often include bottom interaction. Perturbations in the ocean sound speed field can cause changes in the angle of incidence of sound rays with the bottom, which can result in changes to the amount of sound energy lost to the bottom. In lieu of complex transmission loss models, the loss/bounce model provides a simpler way to predict transmission loss changes due to perturbations in the background sound speed field in the ocean. Using an acoustic wavenumber perturbation method, sound speed perturbations, defined by the ocean EOF modes, are translated into a change in the horizontal wavenumber, which in turn changes the modal angle of incidence. The loss/bounce model calculates the loss of sound energy (dB) per bottom bounce over a given distance based on the change in angle of incidence. Evaluated using experimental data from NEST, the loss/bounce model provided accurate predictions of changes to transmission loss due to perturbations of the background sound speed field.

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Acoustic Ducting, Reflection, Refraction, and Dispersion by Curved Nonlinear Internal Waves in Shallow Water

Cited by 71 publications

References 24 publications

Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean

Low-frequency broadband sound source localization using an adaptive normal mode back-propagation approach in a shallow-water ocean

Three-dimensional acoustic propagation through shallow water internal, surface gravity and bottom sediment waves

Environmental analysis and prediction of transmission loss in the region of the New England Shelfbreak

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