Horizontal Refraction in a Three-dimensional Medium of Variable Stratification

Weston, D. E.

doi:10.1088/0370-1328/78/1/308

Cited by 49 publications

(20 citation statements)

References 1 publication

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“…After the introduction of the term "horizontal refraction" by Weston [25], many researchers have tried to explain the horizontal refracted wave for the coastal wedge and seamounts, which have a strong refraction effect due to the sloping bathymetry. Harrison [18,19] derived analytical ray paths caused by repeated reflections at a sloping sea bed, and showed shadow zone boundaries for a seamount.…”

Section: B Horizontal Refractionmentioning

confidence: 99%

Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts

Kim¹

2009

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The Basin Acoustic Seamount Scattering Experiment (BASSEX) of 2004 was conducted to measure forward-scattering around the Kermit-Roosevelt Seamount Complex in the Northeast Pacific. The BASSEX experiment was focused on the bathymetric effects on acoustic propagation, in particular, on direct blockage, horizontal refraction, diffraction, and scattering by the seamounts. A towed hydrophone array, with 64 sensors cut for 250Hz (3m spacing), was used to measure the signals transmitted from the aforementioned broadband sources at many locations around the Kermit-Roosevelt and Elvis seamounts. Utilizing the measured broadband signals from the towed array, the size of the shadow zone was obtained. The measured data in the BASSEX experiment strongly support the understanding of the complicated phenomena of sound propagation around the seamounts. In addition, the experimental data could be used to validate current 2D and 3D theoretical models and develop new models to properly realize the sound propagation with such complicated phenomena.In this thesis, the reconciliation between the measured pulse arrivals from the BASSEX experiment and various two-dimensional (2D) and three-dimensional (3D) theoretical models is carried out to investigate the physical characteristics of the sound propagation around seamounts: First, the 2D Parabolic Equation (PE) model and the 2D ray tracing model are used to reconcile each ray arrival with the BASSEX experiment in terms of arrival time and grazing angle. We construct a sound speed field database based on the sound speed profiles from the BASSEX experiment, World Ocean Atlas (WOA)2005, and CTD casts using the objective analysis.Second, 3D broadband sound propagation around a conical seamount is 4 investigated numerically using the 3D spectral coupled-mode model (W. Luo, PhD Thesis, MIT, 2007). Since the calculation of 3D broadband pulses with the spectral coupledmode model requires extensive computation time, a parallel program is developed with a clustered computing system to obtain results in reasonable time. The validation of the 3D spectral coupled-mode model is performed by a series of comparisons between the various 2D and 3D models for a shallow-water waveguide. The Kermit-Roosevelt seamount is modeled by a simple conical seamount for the 3D model. The computed 3D broadband pulses for the modeled conical seamount are compared with those from the BASSEX experiment and the 2D PE simulation.Through this analysis, we examine the limit of the application of the sound propagation models and improve the efficiency of the 3D sound propagation model using parallel computing to obtain a broadband pulse in a reasonable amount of time.

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Section: B Horizontal Refractionmentioning

confidence: 99%

Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts

Kim¹

2009

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“…Weston [9] has discussed this device and has shown from geometrical arguments that the shape of the horizontally projected ray path is a hyperbola (Fig. 10).…”

Section: R^=[{r-r')^ + Zvi\ R2-[{r + R')^ + Z^^l\mentioning

confidence: 99%

“…The criterion for a ray to correspond to the m th mode is that the grazing angle of the ray at the vertex of its hyperbolic path must be the same as that of the ray corresponding to the mth mode in shallow water whose depth is equal to the depth at the vertex. Weston [9] has shown that the angle between the asymptotes of a hyperbolic ray path and the shoreline is the same as the grazing angle at the vertex. It follows that the criterion given above for a ray to correspond to a mode fixes the directions of the arms of the modal hyperbola.…”

Section: R^=[{r-r')^ + Zvi\ R2-[{r + R')^ + Z^^l\mentioning

confidence: 99%

Acoustic Propagation in a Wedge-Shaped Ocean with Perfectly Reflecting Boundaries

Buckingham¹

1984

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“…This path curvature in the horizontal is known as the horizontal refraction (Refs. [7][8][9][10][11][12]). When such a path leaves the source propagating up-slope, it may be turned around to reach a receiver propagating down-slope.…”

mentioning

confidence: 99%

“…If a receiver is restricted to the main vertical plane, the change in propagation direction is referred to as the backscattering, and indirect paths are referred to as backscattered paths (Refs. [9,13]). …”

mentioning

confidence: 99%

Generalized ray method for three-dimensional propagation in a penetrable wedge

2018

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A generalized ray solution is presented for the three-dimensional (3-D) acoustic field produced by a transient point source in a rigid-bottom, fast-speed fluid-bottom, and fast-speed elastic-bottom wedge modeling a continental shelf environment. The effect of diffraction (scattering) at the wedge apex is ignored in the solution, but nevertheless the solution is exact and complete for the image component of the field, expressed by a sum of partial waves including a pulse emitted from the source plus a finite number of pulses reflected off the wedge boundaries. Time records of the acoustic pressure illustrating 3-D acoustical propagation effects are evaluated at five receivers located at equal radial range in the horizontal from the source, but different orientation to the source, measured by the azimuthal angle assuming values: 0 • (down-slope), 45 • (obliquely down-slope), 90 • (cross-slope), 135 • (obliquely up-slope), and 180 • (up-slope). The arrival times of the spherical and head waves propagating along various paths are evaluated at each receiver for each bottom. It was found that the time interval between the first arrival and the ultimate arrival diminished, and the pulses became more peaked, as the azimuthal angle of the receiver increased. For the rigid-bottom wedge, we have found that all backscattered pulses are significant at the up-slope receiver. For the fluid-bottom wedge, we have found that: at each receiver, the source-pulse is preceded by the ground wave which is much weaker than the water wave; and, at the up-slope receiver, the backscattered pulses are insignificant. For the elastic-bottom wedge, we have found that: at each receiver, the ground-wave-response begins earlier than that in the fluid-bottom wedge, and thus the record separates out into distinct ground-wave and water-wave phases; and, at the up-slope receiver, the backscattered pulses are significant.

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Horizontal Refraction in a Three-dimensional Medium of Variable Stratification

Cited by 49 publications

References 1 publication

Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts

Forward sound propagation around seamounts : application of acoustic models to the Kermit-Roosevelt and Elvis seamounts

Acoustic Propagation in a Wedge-Shaped Ocean with Perfectly Reflecting Boundaries

Generalized ray method for three-dimensional propagation in a penetrable wedge

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