2 edition of **Modelling of high frequency acoustic scattering from a moving rough surface** found in the catalog.

Modelling of high frequency acoustic scattering from a moving rough surface

Raymond Harvey Owen

- 234 Want to read
- 7 Currently reading

Published
**1995**
by University of Birmingham in Birmingham
.

Written in English

**Edition Notes**

Thesis (Ph.D) - University of Birmingham, School of Electronic and Electrical Engineering, 1996.

Statement | by Raymond Harvey Owen. |

ID Numbers | |
---|---|

Open Library | OL21764186M |

Abstract. Statistical properties of acoustic fields scattered from wind-driven surfaces are studied using a numerical simulation technique. The technique consists of the numerical integration of the Helmholtz equation, as further developed by Gulin (Gulin, ), over simulated numerical model surfaces. The scattering of sound from the sea surface is important for the operation of underwater sonar and underwater acoustic communications systems. Studies of low to mid -frequency surface reverberation have a long history, but studies of very high frequency (> kHz) surface scattering in the literature are rare. The physics of very high.

For example, children can hear high-frequency sounds (above Hz) much better than low-frequency sounds (below Hz, bass) (Boeker and van Grondelle, ). However, hearing begins to decline significantly after the age of This change is most pronounced in men and for high-frequency sounds (at or above Hz) (Liu et al., Dr. Thorsos research addresses high-frequency sound penetration into, propagation within, and scattering from the shallow-water seafloor. One finding is that high-frequency acoustic penetration into sediments at grazing angles below the critical angle is possible- .

This volume comprises over fifty contributions resulting from the Ocean Reverberation Symposium, held May in La Spezia, Italy. The contributions are presented in eight sections: Scattering Mechanisms, High Frequency Measurements and Mechanisms, Reverberation Modelling, ARSRP Mid-Atlantic Ridge Experiment, Low Frequency Measurements, Volume Scattering, Signal Processing . where sd is the scattering coefficient due to diffraction and ss is the scattering coefficient due to surface roughness. An example of how the reflection based scattering works is shown in Fig. 6. If a relatively small surface (e.g. a table) reflects sound from a source close to the surface, there is very little scattering, but when the.

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A function of surface heights and of acoustic wavelength. There are already well-known theoretical methods for predicting roughness scattering from rough surface.

One of the most common models is based on the Kirchhoff approximation [5,6] and need large curvature of the rough interface compared to the acoustic wavelength. Another. Acoustic scattering by a rough, possibly dynamic interface is experimentally studied by insonifying the seabed and the sea surface at high frequency at various incident angles.

A directional source working at kHz was placed at the top of a m. The scattering from a rough pressure release surface, where the spectrum of the surface only contains wavelengths considerably shorter than half the acoustic wavelength, is considered.

The acoustic wave scattering properties of a dynamic pressure-release surface boundary are analyzed using a numeric technique based on the finite-difference time-domain (FDTD) method. A technique for studying wave scattering from randomly rough surfaces by computer simulation is presented.

Scattering of ‐ and ‐kHz acoustic waves from numerical models of wind‐driven sea surfaces having Neumann‐Pierson spectra for a 5 m sec −1 wind speed is reported.

The surfaces were generated using the theory of linear systems in two by: The present paper examines the temporal evolution of acoustic fields by modeling forward propagation subject to sea surface dynamics with time scales of less than a second to tens of seconds.

A time-evolving rough sea surface model is combined with a rough surface formulation of a parabolic equation model for predicting time-varying acoustic fields.

Surface waves are generated from surface. Experimental measurements of the normal incidence underwater acoustic backscatter from a model rough surface having Gaussian statistics with a rms height cm and a correlation length cm are presented.

Scattering measurements were obtained over the frequency range 20– kHz for a variety of transmitter and receiver distances from the model surface. The problem of the scattering of harmonic plane waves by a rough half-plane is studied here.

The surface roughness is finite. The slope of the irregularity is taken as arbitrary. Two boundary conditions are considered, those of Dirichlet and Neumann. An asymptotic solution is obtained, when the wavelength λ of the incident wave is much larger than the characteristic length of the roughness l.

better understand how an anisotropic rough surface can impact the acoustic propagation and scattering. The small slope approximation allows us to modify directly the height statistics, either by using true measurements of a rough surface [21] or by using theoretical model via the height covariance function of the seabed to describe its roughness.

Solutions to ocean acoustic scattering problems are often formulated in the frequency domain, which implies that the surface is “frozen” in time. This may be reasonable for short duration signals but breaks down if the surface changes appreciably over the transmission time.

Frequency domain solutions are also impractical for source-receiver ranges and frequency bands typical for. A M is the area of the mean plane of the scattering surface and P(kA, kB) is the scattering surface's spatial power spectrum (or power spectral density function).

kA and kB are the x and y components of the change in the wave vector, respectively. For a rigid rough surface the average intensity, of a bistatic scattered field is. Scattering by Rough Surfaces 15 J. DeSanto Department of Mathematical and Computer Sciences, Colorado School of Mines, Golden, ColoradoU.S.A.

Contents w Introduction 15 w Acoustic Scattering 17 w Electromagnetic Scattering 23 w Solution Methods 25 w Inverse Problems 27 w Other Methods and Discussion 28 w 1. Statistical properties of high frequency acoustic fluctuations induced by rough sea surface Abstract: Probability Density Function (PDF) of the arrival angle and arrival time of high-frequency sound forward scattering from the rough sea surface are predicted by combining the ray-based and surface-based models.

Rough surface scattering models formulating the Kirchhoff tangent plane approximation. Further developments of the theory went along the lines of the Small Perturbation Approximation (SPM) and the Kirchhoff Approximation (KA) (SILVERSANCER ). The most often quoted reference book on wave scattering from rough surfaces is that of.

In this paper, we propose to develop an effective and efficient computational modeling technique to characterize the statistical properties that govern the performance and capacity of an underwater acoustic communication link. Specifically, we consider the challenging shallow water environment with a moving rough sea surface as the primary source of temporal variations.

to low-frequency acoustic scattering from the sea surface where the validity condition can be satisfied. 2'• The valid region of the Kirchhoff approximation, on the other hand, is not well established. The Kirchhoff approximation is gener- ally assumed to apply to "gently undulating" surfaces This paper focuses on statistical characterization of acoustic scattering from slightly rough sea surface with small Rayleigh parameter.

Infinite random rough sea surface is irradiated with a plane wave single-frequency source and the field scattered by this surface is calculated by the Method of Small Perturbation (MSP).

This work is related to modeling of synthetic sonar images of naval mines or other objects. Considered here is the computation of high frequency scattering from the surface of a rigid 3D-object. A variable depth step implementation of the range-dependent acoustic model (RAM) is applied to the modeling of forward scattering from a rough sea surface.

Scattering from a rough, free, fluid surface can be accurately solved with careful treatment of the numerical boundary representing the free surface. Continuous wave (cw) scattering problems can.

The work presented here deals with high-frequency acoustic scattering from an impenetrable object with a ran-domly perturbed surface in two dimensions. Let D ‰ Rd(d = 2;3) be a sound-soft scatterer with [email protected] sam-pled from a certain probability space.

For a given incident ﬁeld uI(x), the scattered ﬁeld u(x) satisﬁes the Helmholtz. In Section 4, delay time and amplitude of single surface bounce path from the measurement data and moving surface ray model are compared; they directly reflect the effects of moving surface and these fluctuations cause the Doppler shift.

The features of the time-varying acoustic channels (relation between the delay time and amplitude, frequency.High-frequency acoustic penetration into seafloor sediment at low grazing angles is of interest for buried mine detection. the phase fronts of the reflected wave can be seen moving up and to the right above the interface.

For this flat surface case, In order to see if the rough surface scattering mechanism could explain the acoustic.