Acoustic mode radiation from the termination of a truncated nonlinear internal gravity wave duct in a shallow ocean area

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

doi:10.1121/1.3203268

Cited by 32 publications

(39 citation statements)

References 22 publications

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“…al. [18] to describe the effects of horizontal acoustic ducting in between internal waves and by McMahon for theoretical studies of Horizontal Lloyds Mirror effect [41]. In the following sections, we will consider three-dimensional mode coupling The SIA has an advantage of its simplicity as it replaces the problem of continuous modal refraction and coupling with discrete modal refraction and coupling at several vertical interfaces.…”

Section: Sharp Interface Approximationmentioning

confidence: 99%

“…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%

“…[16] presented results on intensity fluctuations and their azimuthal dependence for a mobile source acoustic signal. As a result of SW06, studies of three-dimensional low frequency acoustic, including the effects of internal waves natural curvature [17] and termination [18,19], were extensively developed.…”

Section: Introductionmentioning

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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Section: Sharp Interface Approximationmentioning

confidence: 99%

Section: A Multiple 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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“…Snell's law, written in terms of grazing angle with respect to the horizontal boundary of an internal wave duct, is for vertical mode number . Disregarding tunneling effects [14], the critical angle for trapping a mode within an internal wave duct is given by (1) To complete the task of expressing the critical angle in terms of the parameters of depth, internal wave height, and so on, we use perturbation theory. Since we are mainly interested in modeling oceanographic effects due to internal waves, we can take the bottom to be a rigid boundary for simplicity.…”

Section: A Critical Angle Estimationmentioning

confidence: 99%

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

Lynch

Lin

Duda

et al. 2010

IEEE J. Oceanic Eng.

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Abstract-Nonlinear internal waves in shallow water have been shown to be effective ducts of acoustic energy, through theory, numerical modeling, and experiment. To date, most work on such ducting has concentrated on rectilinear internal wave ducts or those with very slight curvature. In this paper, we examine the acoustic effects of significant curvature of these internal waves.(By significant curvature, we mean lateral deviation of the internal wave duct by more than half the spacing between internal waves over an acoustic path, giving a transition from ducting to antiducting.) We develop basic analytical models of these effects, employ fully 3-D numerical models of sound propagation and scattering, and examine simultaneous acoustical and oceanographic data from the 2006 Shallow Water Experiment (SW06). It will be seen that the effects of curvature should be evident in the mode amplitudes and arrival angles, and that observations are consistent with curvature, though with some possible ambiguity with other scattering mechanisms.

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“…A 3-D normal mode method has been used to study canonical environmental models of shelfbreak front systems [1] and nonlinear internal wave ducts [2][3]. 3-D parabolic-equation (PE) wave propagation models with improved split-step marching algorithms [4][5][6] are used to study sound propagation in realistic environments.…”

Section: Approachmentioning

confidence: 99%

Three-Dimensional Shallow Water Acoustics

Lin

2013

Self Cite

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LONG-TERM GOALSBoth physical oceanographic processes and marine geological features in the continental shelf can cause the medium properties to have lateral heterogeneity, so horizontal refraction of sound can occur and produce significant three-dimensional (3-D) sound propagation effects. The long-term goals of this project are targeted on understanding the 3-D acoustic effects caused by the environmental factors existing commonly in the continental shelf and shelfbreak areas. OBJECTIVESOne of the research objectives of this project is to develop efficient and accurate 3D models (both theoretical and numerical models) for studying underwater sound propagation in 3-D ocean environments. The ultimate scientific objective of the proposed work is to study the underlying physics of the 3-D sound propagation effects caused jointly by physical oceanographic processes and geological features. To achieve this goal, individual environmental factor will be first studied and then considered jointly with a unified ocean, seabed and acoustic model. Another major objective is to develop a tangent linear model to predict acoustic fluctuations due to 3-D sound speed perturbation in the water column. This model will be useful for the sensitivity analysis to assess the joint ocean and seabed effects. APPROACHThe technical approaches employed in the 3D sound propagation study include theoretical analysis, numerical computation and real data analysis. A 3-D normal mode method has been used to study canonical environmental models of shelfbreak front systems [1] and nonlinear internal wave ducts [2][3]. 3-D parabolic-equation (PE) wave propagation models with improved split-step marching algorithms [4][5][6] are used to study sound propagation in realistic environments. When the acoustic mode coupling can be neglected, a vertical-mode horizontal-PE model is used. These PE models employ the following higher order operator splitting to increase the PE approximation accuracy.(1)

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Acoustic mode radiation from the termination of a truncated nonlinear internal gravity wave duct in a shallow ocean area

Cited by 32 publications

References 22 publications

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

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

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

Three-Dimensional Shallow Water Acoustics

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