Computer modeling of a vertical array in a stratified ocean
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Computer modeling of a vertical array in a stratified ocean by Lin Li

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Published by Woods Hole Oceanographic Institution in Woods Hole, Mass .
Written in English

Subjects:

  • Underwater acoustics.,
  • Seismograms.

Book details:

About the Edition

The response of vertical arrays at single frequencies (CW) and for homogeneous media is well known. This paper addresses the issues of frequency dependence and sound velocity gradients for the vertical array response in a deep ocean. I have modified the synthetic seismogram code of Neil Frazer, Subhashis Mallick and Dennis Lindwall to address this problem. The code uses a rearrangement of the Kennett reflectivity algorithm (Kennett, 1974, 1983) which computes the geoacoustic response for depth dependent media and pulse sources by the wave number integration method. The generalized Filon method is applied to the slowness integral for an additional increase in speed (Frazer and Gettrust, 1984; Filon, 1928). The original code computes the response of a single source at a specified depth. The new code has several improvements over the previous one. First, it is a much simplified code addressing only acoustic interaction. The total length is about half the length of the original code. Secondly, the code can compute the response of a vertical array of point sources. By changing the phase delay between the sources, we can steer the beam to the places of most interest. Thirdly, the code reduces considerably numerical noise at large offsets. The original work has numerical noise beyond about 30 km offset at 50 Hz which limits the application of reflectivity modeling in long range problems. The improvement comes with the optimization of the program, both in the speed and program structure. The improved algorithm can be used to get the far offset response (up to 150 km) of a vertical array in the deep ocean at frequencies up to at least 250 Hz. The modeling results are compared to analytical and benchmark solutions. The modified reflectivity code can be applied to the study of pulsed-vertical array sources such as were deployed on the ARSRP (Acoustic Reverberation Special Research Program) acoustic cruises.

Edition Notes

Statementby Lin Li.
SeriesWHOI -- 95-02., WHOI (Series) -- 95-02.
ContributionsWoods Hole Oceanographic Institution.
The Physical Object
Pagination78 p. :
Number of Pages78
ID Numbers
Open LibraryOL15418397M

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Download PDF: Sorry, we are unable to provide the full text but you may find it at the following location(s): (external link).   The tower contained a vertical array of acoustic Doppler velocimeters and fast‐response conductivity‐temperature sensors, providing a nearly continuous data set of turbulent velocity and density fluctuations and a unique look into the stratified turbulence by: A method is derived for instantaneous source-range estimation in a horizontally stratified ocean waveguide from passive beam-time intensity data obtained after conventional plane-wave beamforming of acoustic array measurements. The method has advantages over existing source localization methods, such as matched field processing or the waveguide invariant. Ocean modelling uses a mathematical model of the general circulation of an ocean, based on the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources (radiation, latent heat). These equations are the basis for complex computer programs commonly used for simulating the atmosphere or ocean of the Earth.

nate models retain a fixed vertical position as determined by the static depth of a grid cell, and so this is an Eulerian verti-cal coordinate. Horizontal coordinates in most ocean models remain fixed in space, and so are Eulerian. choice of vertical coordinate is fundamental to the numerical algorithms of an ocean model. Indeed, the standard conceptual model of a bottom mixed layer (i.e., vertical variations in density are much smaller than the variations across the layer boundary) under a stratified interior is that the presence of stratification acts to dampen vertical velocity fluctuations and limits vertical penetration of the bottom‐generated TKE.   A deep vertical line array (VLA) can leverage the steep vertical angles and low loss of RAP arrivals from nearby targets to discriminate them from distant shipping noise, which experiences increased transmission loss (TL) and arrives near horizontal. However, nearby interferers also experience favorable RAP propagation and arrive at steep angles, presenting a challenge for a VLA which lacks. The model of Franks and Chen () of processes at the Georges Bank fronts emphasizes, as noted previously, the decoupling of phytoplankton and herbivores in the mixed zone alongside the front (compared with the spatial balance achieved on the stratified side of the front), and the consequent release from grazing pressure on the autotrophs.

  D.L. Rudnick, in Encyclopedia of Ocean Sciences (Second Edition), Turbulence and Mixing. The upper ocean is distinguished from the interior of the ocean partly because of the very high levels of turbulence present (see Breaking Waves and Near-Surface Turbulence and Upper Ocean Mixing Processes).The smallest scale of motion worthy of note in the ocean is the Kolmogoroff scale, . A linear stratified ocean model is used to study the wind-driven response of the equatorial ocean. The model is an extension of the Lighthill () model that allows the diffusion of heat and momentum into the deeper ocean, and so can develop non-trivial steady solutions. To retain the ability to expand solutions into sums of vertical normal modes, mixing coefficients must be inversely.   The vertical directionality of ambient noise is strongly influenced by seabed reflections. Therefore, potentially, geoacoustic parameters can be inferred by inversion of the noise. In this approach, using vertical array measurements, the reflection loss is found directly by comparing the upward- with the downward-going noise. Theory suggests that this simple ratio is, in fact, the power. The vertical directionality of acoustic ambient noise has been a subject of much interest in the past. It is a well-defined physical quantity that can be measured experimentally with a vertical array.