Acoustic Scattering Into Shadow Zones from Atmospheric Turbulence PDF Download
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Languages : en
Pages : 0
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Book Description
When acoustic scattering estimates are desired from atmospheric regions containing fully developed isotropic homogeneous turbulence, scattering formulas based upon statistical representations of the turbulence well represent the experimental results. However, there is a class of battlefield scenarios where these provisos of fully developed, isotropic and homogeneous sometimes do not apply. The example of this class that is most familiar is that of source and detector near the ground. At ground level, the wind velocity is zero, while at altitude it is not. Thus a gradient of wind velocity exists. There exists often a temperature gradient caused by heating or cooling of the air by contact with the ground. These gradients are recognized in propagation codes by modeling the atmosphere as stratified with each stratum bounded by planes parallel to the assumed flat ground. The anisotropy of the atmosphere near the ground recognized in propagation codes carries over into the generation of turbulence. The above discussion leads to the conclusion that anisotropy in turbulence is to be expected in scenarios played out near the ground, scenarios common to Army operations. The understanding that high sound levels in shadow zones (those regions in an acoustical field in which no sound can reach if the field is determined by ray theory) is caused by scattering from turbulence is very important. This importance arises from the possibility that shadow zone sensors may be used to achieve passive non-line-of-sight detection of enemy assets. This paper unites the above considerations by calculating the shadow zone signal level for a representative battlefield scenario using a structural model of turbulence.
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Languages : en
Pages : 0
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Book Description
When acoustic scattering estimates are desired from atmospheric regions containing fully developed isotropic homogeneous turbulence, scattering formulas based upon statistical representations of the turbulence well represent the experimental results. However, there is a class of battlefield scenarios where these provisos of fully developed, isotropic and homogeneous sometimes do not apply. The example of this class that is most familiar is that of source and detector near the ground. At ground level, the wind velocity is zero, while at altitude it is not. Thus a gradient of wind velocity exists. There exists often a temperature gradient caused by heating or cooling of the air by contact with the ground. These gradients are recognized in propagation codes by modeling the atmosphere as stratified with each stratum bounded by planes parallel to the assumed flat ground. The anisotropy of the atmosphere near the ground recognized in propagation codes carries over into the generation of turbulence. The above discussion leads to the conclusion that anisotropy in turbulence is to be expected in scenarios played out near the ground, scenarios common to Army operations. The understanding that high sound levels in shadow zones (those regions in an acoustical field in which no sound can reach if the field is determined by ray theory) is caused by scattering from turbulence is very important. This importance arises from the possibility that shadow zone sensors may be used to achieve passive non-line-of-sight detection of enemy assets. This paper unites the above considerations by calculating the shadow zone signal level for a representative battlefield scenario using a structural model of turbulence.
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Category :
Languages : en
Pages : 50
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Acoustical scattering from atmospheric turbulence is of interest to the Army because it has been identified as a candidate cause of higher than expected sound levels in shadow zones. Shadow zones are those regions where ray theory indicates no sound penetrates. Scattering into these zones may give non- line-of-sight detection through acoustic detection. This report documents the creation of a computer code for acoustic scattering from a collection of turbules or eddies. The picture is a collection of turbules of different sizes with a specified number density in each size increment. In this aspect, the picture is similar to that of optical scattering from atmospheric aerosols where there is a collection of particles of different sizes with a specified size distribution. The optical scattering code AGAUS is the starting point for creation of the Acoustic SCattering from Turbules code, ASCT, which will for acoustic scattering accomplish what AGAUS accomplishes for optical scattering. The similarities and differences between the two types of scattering are pointed out as they influence the computational algorithm.
Author: Harry J. Auvermann
Publisher:
ISBN:
Category : Backscattering
Languages : en
Pages : 19
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Author: Thomas Rossing
Publisher: Springer Science & Business Media
ISBN: 0387304460
Category : Science
Languages : en
Pages : 1179
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Book Description
This is an unparalleled modern handbook reflecting the richly interdisciplinary nature of acoustics edited by an acknowledged master in the field. The handbook reviews the most important areas of the subject, with emphasis on current research. The authors of the various chapters are all experts in their fields. Each chapter is richly illustrated with figures and tables. The latest research and applications are incorporated throughout, including computer recognition and synthesis of speech, physiological acoustics, diagnostic imaging and therapeutic applications and acoustical oceanography. An accompanying CD-ROM contains audio and video files.
Author: John Brasse
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Category :
Languages : en
Pages :
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Author:
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Category :
Languages : en
Pages : 0
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The objective of the ASL research effort in acoustic propagation is to provide the Army with a multi-stream model for investigating acoustic detection systems. The first step in developing this model is to account for turbulent scattering. Five elements are necessary to accomplish this step: (1) model the turbulent region as a collection of vortices with a distribution of characteristic sizes/velocities; (2) characterize each vortex (turbule) as a known (or assumed) velocity distribution in three space; (3) solve the fluid equations to determine the scattering from each turbule; (4) sum the contributions to the scattered sound pressure level at the detector location of all turbules accounting for the propagation characteristics of the atmospheric medium; and (5) incorporate the algorithms devised above into existing (or appropriately modified) propagation models. Progress in these five areas will be reported.
Author:
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Category : Aeronautics
Languages : en
Pages : 440
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Author: Xunren Yang
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 3110311534
Category : Science
Languages : en
Pages : 392
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Book Description
This book concisely expounds the fundamental concepts, phenomena, theories and procedures in a complete and systematic sense. In this book, not only almost all the important achievements from predecessors but also the contributions from the author himself have been summed up profoundly. Starting from the derivation of fundamental equations, various classical acoustical phenomena such as reflection, refraction, scattering diffraction and absorption in atmosphere, as well as the influences of gravitation and rotation of the earth on the behaviors of different atmospheric waves including acoustic waves, have been discussed in viewpoints of wave acoustics and geometrical acoustics respectively. The recent developments of several computation methods in the field of atmospheric acoustics have been introduced in some detail. As for the application aspects, atmospheric remote sensing has been discussed from the angle of inverse problems.
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Category :
Languages : en
Pages : 13
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From a complete set of fluid equations, a complete set of coupled linear differential equations for the acoustic pressure, temperature, mass density, and velocity in the presence of stationary turbulence may be derived. To first order in the turbulent temperature variation and flow velocity, these coupled acoustic equations yield an acoustic wave equation given in the literature. Further reduction of this wave equation results in a second equation given in the literature which is good for turbulent length scales alpha much greater than the acoustic wavelength lambda. The length scale alpha(s) of the scattering volume is found to be just as important as alpha and lambda in predicting the general behavior of acoustic scattering by turbulence. In particular, if alpha alpha(s), then the first Born temperature and velocity scattering amplitudes for any ratio alpha/lambda are the usual ones predicted by the first equation, and both the forward and backward velocity scattering are essentially zero for solenoidal turbulent flow velocity. The latter is not true if alpha alpha(s). If a /= alpha(s) > > lambda, then the first Born scattering amplitudes are those predicted by the second equation. If lambda >/= alpha >/= alpha(s), other forms result for the scattering amplitudes. Implications of these findings for predicting results of acoustical scattering experiments where the scattering volume is often ill defined are discussed.
Author: Hans Slabbekoorn
Publisher: Springer
ISBN: 1493985744
Category : Medical
Languages : en
Pages : 322
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Book Description
Over the past several years, many investigators interested in the effects of man-made sounds on animals have come to realize that there is much to gain from studying the broader literature on hearing sound and the effects of sound as well as data from the effects on humans. It has also become clear that knowledge of the effects of sound on one group of animals (e.g., birds or frogs) can guide studies on other groups (e.g., marine mammals or fishes) and that a review of all such studies together would be very useful to get a better understanding of the general principles and underlying cochlear and cognitive mechanisms that explain damage, disturbance, and deterrence across taxa. The purpose of this volume, then, is to provide a comprehensive review of the effects of man-made sounds on animals, with the goal of fulfilling two major needs. First, it was thought to be important to bring together data on sound and bioacoustics that have implications across all taxa (including humans) so that such information is generally available to the community of scholars interested in the effects of sound. This is done in Chaps. 2-5. Second, in Chaps. 6-10, the volume brings together what is known about the effects of sound on diverse vertebrate taxa so that investigators with interests in specific groups can learn from the data and experimental approaches from other species. Put another way, having an overview of the similarities and discrepancies among various animal groups and insight into the “how and why” will benefit the overall conceptual understanding, applications in society, and all future research.
