Horizontal refraction of propagating sound due to seafloor scours over a range-dependent layered bottom on the New Jersey shelf

Abstract

Three-dimensional propagation effects of low frequency sound from 100 to 400 Hz caused by seafloor topography and range-dependent bottom structure over a 20 km range along the New Jersey shelf are investigated using a hybrid modeling approach. Normal modes are used in the vertical dimension, and a parabolic-equation approximate model is applied to solve the horizontal refraction equation. Examination of modal amplitudes demonstrates the effect of environmental range dependence on modes trapped in the water column, modes interacting with the bottom, and modes trapped in the bottom. Using normal mode ray tracing, topographic features responsible for threedimensional effects of horizontal refraction and focusing are identified. These effects are observed in the measurements from the Shallow Water 2006 experiment. Specifically, signals from a pair of fixed sources recorded on a horizontal line array sitting on the seafloor show an intensification caused by horizontal focusing due to the seabed topography of 4 dB along the array.

Comparisons of laboratory scale measurements of three-dimensional acoustic propagation with solutions by a parabolic equation model

“…However, during the calibration phase over a flat bottom, 20 it appeared more reasonable to consider a value within (1700 6 50) m/s due to an apparently different consolidation of the sand in the tank. The density of the sandy bottom was measured to be (1.99 6 0.01) g/cm 3 . The value of the bottom sound attenuation could not be measured at the central frequency (150 kHz) considered in the tank experiment (see discussion hereafter).…”

“…15, the scale factor of 1000:1 was applied in all the simulations, where the frequencies and lengths have been appropriately modified (but keeping the 0.5 dB per wavelength value for the compressional attenuation coefficient in the fluid bottom layer), to show the analogy between propagation in the tank and an oceanic waveguide. The wedge-shaped computational domain consists of a lossless homogeneous water layer with the relevant value of the sound speed (1488.2 m/s for ASP-H1, and 1488.7 m/s for both ASP-H2 and ASP-H3) and a density of 1 g/cm 3 , overlying a lossy half-space sediment bottom truncated at a depth of 600 m below the seafloor, with a homogeneous sound speed of 1700 m/s, a density of 1.99 g/cm 3 , and a sound attenuation of 0.5 dB per wavelength. For each comparison, separate runs of the 3-D PE code were performed using the MAP estimates of the geometrical parameters as given in Table I for the respective data set.…”

“…1, and references therein). More recently, renewed interested stimulated by experimental evidence of 3-D propagation [2][3][4][5][6] has given rise to an increasing number of publications reporting developments in theoretical and numerical 3-D modeling. [7][8][9][10][11][12][13] Of particular importance is the establishment of test cases for 3-D model validation and performance comparison.…”

Three-Dimensional Scale-Model Tank Experiment of the Hudson Canyon Region

“…[1][2][3][4][5][6][7] These models have the potential to be very accurate, but comparisons between data taken at sea and numerical predictions often suffer because of insufficient environmental inputs to the numerical model. This is already a problem for two-dimensional (2D) data-model comparisons and is likely to be a perpetual problem when trying to employ 3D numerical models to describe experimental data.…”

Variability of phase and amplitude fronts due to horizontal refraction in shallow water

“…Subsequently, the following phenomena were studied: focusing/defocusing of the sound field in the horizontal plane in the presence of nonlinear internal waves Badiey et al, 2005); variations of the interference pattern in the horizontal plane in the area of a coastal wedge in (Deane and Buckingham, 1993;Katsnelson et al, 2013), or in the area of the underwater canyon in (Duda et al, 2011;Y.-T. Lin, 2013); multipath propagation in the horizontal plane in an experiment in the Florida Strait (Heaney and Murray, 2009); and many others. In the papers (Bender et al, 2014;Ballard et al, 2012), the importance of taking horizontal refraction into account for inverse problems was discussed as well.…”