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Journal of the Acoustical Society of America

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Apr 2011

Volume 129, Issue 4, pp. EL101-2700

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Sound speed in water-saturated glass beads as a function of frequency and porosity

Theodore F. Argo, IV, Matthew D. Guild, Preston S. Wilson, Matthias Schröter, Charles Radin, and Harry L. Swinney

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL101-EL107 (2011); (7 pages)

Online Publication Date: 22 Mar 2011

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Sound propagation in water-saturated granular sediments is known to depend on the sediment porosity, but few data in the literature address both the frequency and porosity dependency. To begin to address this deficiency, a fluidized bed technique was used to control the porosity of an artificial sediment composed of glass spheres of 265 μm diameter. Time-of-flight measurements and the Fourier phase technique were utilized to determine the sound speed for frequencies from 300 to 800 kHz and porosities from 0.37 to 0.43. A Biot-based model qualitatively describes the porosity dependence.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
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Distortion-product otoacoustic-emission suppression tuning in human infants and adults using absorbed sound power

Douglas H. Keefe and Carolina Abdala

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL108-EL113 (2011); (6 pages) | Cited 2 times

Online Publication Date: 22 Mar 2011

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The greatest difference in distortion product otoacoustic emission (DPOAE) suppression tuning curves (STCs) in infant and adult ears occurs at a stimulus frequency of 6 kHz. These infant and adult STCs are much more similar when constructed using the absorbed power level of the stimulus and suppressor tones rather than using sound pressure level. This procedure incorporates age-related differences in forward and reverse transmission of sound power through the ear canal and middle ear. These results support the theory that the cochlear mechanics underlying DPOAE suppression are substantially mature in full-term infants.
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43.64.Jb Otoacoustic emissions
43.64.Ha Acoustical properties of the outer ear; middle-ear mechanics and reflex
43.64.Kc Cochlear mechanics
43.64.Yp Instruments and methods
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Equivalent contributing depth investigated by a lateral wave with axial transmission in viscoelastic cortical bone

Guillaume Haïat, Salah Naili, Mai Ba Vu, Christophe Desceliers, and Christian Soize

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL114-EL120 (2011); (7 pages) | Cited 1 time

Online Publication Date: 22 Mar 2011

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Cortical bone is a viscoelastic heterogeneous medium which may be assessed with axial transmission. This work aims at evaluating the average depth investigated by the lateral wave for radial variations of material properties in relatively thick cortical bone. The equivalent contributing depth (ECD) is derived from the finite element simulation results for spatial variations of a viscoelastic coefficient (η11) and of porosity. A value of ECD equal to around 1.6 mm is obtained for a spatial variation of η11. The method fails to predict accurate values of the ECD for a spatial variation of porosity, because all parameters vary simultaneously.
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43.80.Ev Acoustical measurement methods in biological systems and media
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.58.Ta Computers and computer programs in acoustics
43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.80.Qf Medical diagnosis with acoustics
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Airframe structural damage detection: A non-linear structural surface intensity based technique

Fabio Semperlotti, Stephen C. Conlon, and Andrew R. Barnard

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL121-EL127 (2011); (7 pages)

Online Publication Date: 24 Mar 2011

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The non-linear structural surface intensity (NSSI) based damage detection technique is extended to airframe applications. The selected test structure is an upper cabin airframe section from a UH-60 Blackhawk helicopter (Sikorsky Aircraft, Stratford, CT). Structural damage is simulated through an impact resonator device, designed to simulate the induced vibration effects typical of non-linear behaving damage. An experimental study is conducted to prove the applicability of NSSI on complex mechanical systems as well as to evaluate the minimum sensor and actuator requirements. The NSSI technique is shown to have high damage detection sensitivity, covering an extended substructure with a single sensing location.
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43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
43.40.Ga Nonlinear vibration
43.40.At Experimental and theoretical studies of vibrating systems
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Analysis of high-frequency wind-driven ambient noise in shallow brackish water

Ari Poikonen

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL128-EL134 (2011); (7 pages)

Online Publication Date: 24 Mar 2011

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Ambient noise spectra in a shallow brackish water environment were found to be steeper than expected at frequencies above 10 kHz. The high-frequency behavior of the spectra was resolved by modeling dispersion and noise in bubbly water. Bubble size distributions fitted to the brackish water spectra exhibit a distinctive maximum in the radius range 0.1–0.3 mm, and a substantial drop in bubble density below a radius of 0.1 mm. The brackish water distributions were tied to an oceanic spectrum with a spectral slope of 5.7 dB/octave obtained with a −3/2 power law dependence of bubble size density on radius.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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Improving beampatterns of two-dimensional random arrays using convex optimization

Peter Gerstoft and William S. Hodgkiss

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL135-EL140 (2011); (6 pages)

Online Publication Date: 28 Mar 2011

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Sensors are becoming ubiquitous and can be combined in arrays for source localization purposes. If classical conventional beamforming is used, then random arrays have poor beampatterns. By pre-computing sensor weights, these beampatterns can be improved significantly. The problem is formulated in the frequency domain as a desired look direction, a frequency-independent transition region, and the power minimized in a rejection-region. Using this formulation, the frequency-dependent sensor weights can be obtained using convex optimization. Since the weights are data independent they can be pre-computed, the beamforming has similar computational complexity as conventional beamforming. The approach is demonstrated for real 2D arrays.
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43.60.Fg Acoustic array systems and processing, beam-forming
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Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves

Mohsen Badiey, Boris G. Katsnelson, Ying-Tsong Lin, and James F. Lynch

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL141-EL147 (2011); (7 pages) | Cited 4 times

Online Publication Date: 28 Mar 2011

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Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd’s mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Es Velocity, attenuation, refraction, and diffraction in water, Doppler effect
43.30.Dr Hybrid and asymptotic propagation theories, related experiments
43.30.Bp Normal mode propagation of sound in water
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Effects of natural sounds on the perception of road traffic noise

Bert De Coensel, Sofie Vanwetswinkel, and Dick Botteldooren

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL148-EL153 (2011); (6 pages) | Cited 1 time

Online Publication Date: 28 Mar 2011

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Recent studies show that introducing sound from water features in urban open spaces may reduce the loudness of road traffic noise, but it is not clear in which situations this measure also improves overall soundscape quality. This work describes a listening experiment on loudness, pleasantness, and eventfulness of stimuli that combine road traffic noise with fountain or bird sound at different sound levels. Adding fountain sound reduced the loudness of road traffic noise only if the latter had low temporal variability. Conversely, adding bird sound significantly enhanced soundscape pleasantness and eventfulness, more than what was achieved by adding fountain sound.
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43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.50.Qp Effects of noise on man and society
43.66.Lj Perceptual effects of sound
43.66.Ba Models and theories of auditory processes
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On the aeroacoustic tonal noise generation mechanism of a sharp-edged plate

Danielle J. Moreau, Laura A. Brooks, and Con J. Doolan

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. EL154-EL160 (2011); (7 pages)

Online Publication Date: 28 Mar 2011

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This letter presents an experimental study on the tonal noise generated by a sharp-edged flat plate at low-to-moderate Reynolds number. Flow and far-field noise data reveal that, in this particular case, the tonal noise appears to be governed by vortex shedding processes. Also related to the existence of the tonal noise is a region of separated flow slightly upstream of the trailing edge. Hydrodynamic fluctuations at selected vortex shedding frequencies are strongly amplified by the inflectional mean velocity profile in the separated shear layer. The amplified hydrodynamic fluctuations are diffracted by the trailing edge, producing strong tonal noise.
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43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence
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Acoustic radiation torque and the conservation of angular momentum (L)

Likun Zhang and Philip L. Marston

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1679-1680 (2011); (2 pages)

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This note concerns the evaluation of the static acoustic radiation torque exerted by an acoustic field on a scatterer immersed in a nonviscous fluid based on far-field scattering. The radiation torque is expressed as the integral of the time-averaged flux of angular momentum over a spherical surface far removed from the scattering object with its center at the centroid of the object. That result was given previously [G. Maidanik, J. Acoust. Soc. Am. 30, 620–623 (1956)]. Another expression given recently [Z. W. Fan et al., J. Acoust. Soc. Am. 124, 2727–2732 (2008)] is simplified to this formula. Comments are made on obtaining it directly from the general theorem of angular momentum conservation in the integral form.
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43.25.Qp Radiation pressure

Transmission loss measurement of acoustic material using time-domain pulse-separation method (L)

Liang Sun and Hong Hou

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1681-1684 (2011); (4 pages) | Cited 1 time

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An alternative method for measuring the normal incidence sound transmission loss (nSTL) is presented in this paper based on the time-domain separation of so-called Butterworth pulse with a short-duration time about 1 ms in a standing wave tube. During the generation process of the pulse, inverse filter principle was adopted to compensate the loudspeaker response, besides this, the effect of the characteristics of tube termination can be eliminated through the generation process of the pulse so as to obtain a single plane pulse wave in the standing wave tube which makes the nSTL measurement very simple. A polyurethane foam material with low transmission loss and a kind of rubber material with relatively high transmission loss are used to verify the proposed method. When compared with the traditional two-load method, a relatively good agreement between these two methods can be observed. The main error of this method results from the measuring accuracy of the amplitude of transmission coefficient.
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43.58.Gn Acoustic impulse analyzers and measurements
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Multiple scattering by random configurations of circular cylinders: Reflection, transmission, and effective interface conditions

P. A. Martin

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1685-1695 (2011); (11 pages) | Cited 2 times

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In a previous paper, Linton and Martin [J. Acoust. Soc. Am. 117, 3413–3423 (2005)] obtained two formulas for the effective wavenumber in a dilute random array of circular scatterers. They emerged from a study of the problem of the reflection of a plane wave at oblique incidence to a half-space containing the scatterers. Here, their study is extended to obtain formulas for the reflection and transmission coefficients and to investigate the average fields near the boundary of the half-space. Comparisons with previous work are made.
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43.20.Fn Scattering of acoustic waves
43.20.Bi Mathematical theory of wave propagation
43.20.Hq Velocity and attenuation of acoustic waves

Prediction of sound reflection by corrugated porous surfaces

J.-F. Allard, O. Dazel, G. Gautier, J.-P. Groby, and W. Lauriks

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1696-1706 (2011); (11 pages) | Cited 1 time

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The coupled mode (CM) and finite-element methods (FEMs) are developed and used to predict the acoustic reflection coefficient of a semi-infinite porous medium with closely spaced two-dimensional (2D) periodical corrugations. These methods are also applied to predict the reflection coefficient of a periodic array of porous corrugations installed on an acoustically rigid surface. It is shown that the predictions by the both methods agree closely. The reflection coefficient and Brewster angle of total refraction for the corrugated semi-infinite medium predicted with these methods are compared against that predicted by the Biot/Tolstoy/Howe/Twersky and extended Twersky models. A similar analysis is carried out for porous corrugations set on a rigid backing. The behavior of the reflection coefficient and the pole in the expression for the reflection coefficient located close to grazing incidence is studied.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance

Anomalous waveforms observed in laboratory-formed gas hydrate-bearing and ice-bearing sediments

Myung W. Lee and William F. Waite

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1707-1720 (2011); (14 pages)

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Acoustic transmission measurements of compressional, P, and shear, S, wave velocities rely on correctly identifying the P- and S-body wave arrivals in the measured waveform. In cylindrical samples for which the sample is much longer than the acoustic wavelength, these body waves can be obscured by high-amplitude waveform features arriving just after the relatively small-amplitude P-body wave. In this study, a normal mode approach is used to analyze this type of waveform, observed in sediment containing gas hydrate or ice. This analysis extends an existing normal-mode waveform propagation theory by including the effects of the confining medium surrounding the sample, and provides guidelines for estimating S-wave velocities from waveforms containing multiple large-amplitude arrivals.
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43.20.Ks Standing waves, resonance, normal modes
43.60.Bf Acoustic signal detection and classification, applications to control systems
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Measurement of material nonlinearity using surface acoustic wave parametric interaction and laser ultrasonics

Theodosia Stratoudaki, Robert Ellwood, Steve Sharples, Matthew Clark, Michael G. Somekh, and Ian J. Collison

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1721-1728 (2011); (8 pages) | Cited 2 times

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A dual frequency mixing technique has been developed for measuring velocity changes caused by material nonlinearity. The technique is based on the parametric interaction between two surface acoustic waves (SAWs): The low frequency pump SAW generated by a transducer and the high frequency probe SAW generated and detected using laser ultrasonics. The pump SAW stresses the material under the probe SAW. The stress (typically <5 MPa) is controlled by varying the timing between the pump and probe waves. The nonlinear interaction is measured as a phase modulation of the probe SAW and equated to a velocity change. The velocity–stress relationship is used as a measure of material nonlinearity. Experiments were conducted to observe the pump–probe interaction by changing the pump frequency and compare the nonlinear response of aluminum and fused silica. Experiments showed these two materials had opposite nonlinear responses, consistent with previously published data. The technique could be applied to life-time predictions of engineered components by measuring changes in nonlinear response caused by fatigue.
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43.25.Dc Nonlinear acoustics of solids
43.25.Fe Effect of nonlinearity on acoustic surface waves
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission

“Compression-only” behavior: A second-order nonlinear response of ultrasound contrast agent microbubbles

Jeroen Sijl, Marlies Overvelde, Benjamin Dollet, Valeria Garbin, Nico de Jong, Detlef Lohse, and Michel Versluis

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1729-1739 (2011); (11 pages) | Cited 6 times

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Oscillating phospholipid-coated ultrasound contrast agent microbubbles display a so-called “compression-only” behavior, where it is observed that the bubbles compress efficiently while their expansion is suppressed. Here, a theoretical understanding of the source of this nonlinear behavior is provided through a weakly nonlinear analysis of the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499–3505 (2005)]. It is shown that the radial dynamics of the bubble can be considered as a superposition of a linear response at the fundamental driving frequency and a second-order nonlinear low-frequency response that describes the negative offset of the mean bubble radius. The analytical solution deduced from the weakly nonlinear analysis shows that the compression-only behavior results from a rapid change of the shell elasticity with bubble radius. In addition, the radial dynamics of single phospholipid-coated microbubbles was recorded as a function of both the amplitude and the frequency of the driving pressure pulse. The comparison between the experimental data and the theory shows that the magnitude of compression-only behavior is mainly determined by the initial phospholipids concentration on the bubble surface, which slightly varies from bubble to bubble.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.25.Ts Nonlinear acoustical and dynamical systems
43.35.Ei Acoustic cavitation in liquids
43.80.Qf Medical diagnosis with acoustics
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A computational study of the effect of windscreen shape and flow resistivity on turbulent wind noise reduction

Ying Xu, Z. C. Zheng, and D. K. Wilson

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1740-1747 (2011); (8 pages)

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In this paper, numerical simulations are used to study the turbulent wind noise reduction effect of microphone windscreens with varying shapes and flow resistivities. Typical windscreen shapes consisting of circular, elliptical, and rectangular cylinders are investigated. A turbulent environment is generated by placing a solid circular cylinder upstream of the microphone. An immersed-boundary method with a fifth-order weighted essentially non-oscillatory scheme is implemented to enhance the simulation accuracy for high-Reynolds number flow around the solid cylinder as well as at the interface between the open air and the porous material comprising the windscreen. The Navier–Stokes equations for incompressible flow are solved in the open air. For the flow inside the porous material, a modified form of the Zwikker–Kosten equation is solved. The results show that, on average, the circular and horizontal ellipse windscreens have similar overall wind noise reduction performance, while the horizontal ellipse windscreen with medium flow resistivity provides the most effective wind noise reduction among all the considered cases. The vertical ellipse windscreen with high flow resistivity, in particular, increases the wind noise because of increased self-generation of turbulence.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.28.Ra Generation of sound by fluid flow, aerodynamic sound and turbulence

Variations in recorded acoustic gunshot waveforms generated by small firearms

Steven D. Beck, Hirotaka Nakasone, and Kenneth W. Marr

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1748-1759 (2011); (12 pages)

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Analysis of recorded acoustic gunshot signals to determine firearm waveform characteristics requires an understanding of the impulsive signal events, how the waveforms vary among different sources, and how the waveforms are affected by the environment and the recording system. This paper presents empirical results from waveforms produced by different small firearms and an analysis of their variations under different and controlled conditions. Acoustic signals were generated using multiple firearm makes and models firing different ammunition types. Simultaneous recordings from the microphones located at different distances from the source and at different azimuth angles (from the line-of-fire) were used to study source characteristics and sound propagation effects. The results indicate that recorded gunshot waveforms generally consist of multiple acoustic events, and these are observable depending on the received distance and azimuth angle. The source blast size, microphone distance, and microphone azimuth angle are the primary factors affecting the recorded muzzle blast characteristics. Ground or object reflections and ballistic shockwaves and their reflections can interfere with the muzzle blast waveform and its measurements. This experiment confirmed and quantified the wide range of correlation results between waveforms recorded from different source, microphone distance, and microphone angle configurations.
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43.28.Mw Shock and blast waves, sonic boom
43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields

Nonlinear and diffraction effects in propagation of N-waves in randomly inhomogeneous moving media

Mikhail Averiyanov, Philippe Blanc-Benon, Robin O. Cleveland, and Vera Khokhlova

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1760-1772 (2011); (13 pages) | Cited 2 times

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Finite amplitude acoustic wave propagation through atmospheric turbulence is modeled using a Khokhlov–Zabolotskaya–Kuznetsov (KZK)-type equation. The equation accounts for the combined effects of nonlinearity, diffraction, absorption, and vectorial inhomogeneities of the medium. A numerical algorithm is developed which uses a shock capturing scheme to reduce the number of temporal grid points. The inhomogeneous medium is modeled using random Fourier modes technique. Propagation of N-waves through the medium produces regions of focusing and defocusing that is consistent with geometrical ray theory. However, differences up to ten wavelengths are observed in the locations of fist foci. Nonlinear effects are shown to enhance local focusing, increase the maximum peak pressure (up to 60%), and decrease the shock rise time (about 30 times). Although the peak pressure increases and the rise time decreases in focal regions, statistical analysis across the entire wavefront at a distance 120 wavelengths from the source indicates that turbulence: decreases the mean time-of-flight by 15% of a pulse duration, decreases the mean peak pressure by 6%, and increases the mean rise time by almost 100%. The peak pressure and the arrival time are primarily governed by large scale inhomogeneities, while the rise time is also sensitive to small scales.
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43.28.Mw Shock and blast waves, sonic boom
43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.28.Lv Statistical characteristics of sound fields and propagation parameters
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Quasi-Gaussian Bessel-beam superposition: Application to the scattering of focused waves by spheres

Philip L. Marston

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1773-1782 (2011); (10 pages) | Cited 1 time

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A superposition of zero-order Bessel beams is examined that closely resembles an idealized paraxial Gaussian beam, provided the superposition is not tightly focused. Plots compare wavefield properties in the focal region and in the far field for different values of kw0, the product of the wavenumber k, and the focal-spot-radius w0. The superposition (which is an exact solution of the Helmholtz equation) has the important property that the scattering by an isotropic sphere can be calculated without any approximations for the commonly considered case of linear waves propagating in an inviscid fluid. The nth partial wave amplitude is similar to the case of plane-wave illumination except for a weighting factor that depends on incomplete gamma functions. An approximation for the weighting factor is also discussed based on a generalization of the Van de Hulst localization principle for a sphere of radius a at the focus of a Gaussian beam. Examples display differences between the directionality of the scattering with the plane wave case even though for the cases displayed, ka does not exceed 2 and w0/a is not less than 2. Properties of tightly focused wavefields and the partial wave weighting factors are discussed.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.20.Fn Scattering of acoustic waves
43.40.Fz Acoustic scattering by elastic structures
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions

A field expansions method for scattering by periodic multilayered media

Alison Malcolm and David P. Nicholls

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1783-1793 (2011); (11 pages) | Cited 2 times

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The interaction of acoustic and electromagnetic waves with periodic structures plays an important role in a wide range of problems of scientific and technological interest. This contribution focuses upon the robust and high-order numerical simulation of a model for the interaction of pressure waves generated within the earth incident upon layers of sediment near the surface. Herein described is a boundary perturbation method for the numerical simulation of scattering returns from irregularly shaped periodic layered media. The method requires only the discretization of the layer interfaces (so that the number of unknowns is an order of magnitude smaller than finite difference and finite element simulations), while it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic of boundary integral/element methods. The approach is a generalization to multiple layers of Bruno and Reitich’s “Method of Field Expansions” for dielectric structures with two layers. By simply considering the entire structure simultaneously, rather than solving in individual layers separately, the full field can be recovered in time proportional to the number of interfaces. As with the original field expansions method, this approach is extremely efficient and spectrally accurate.
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43.30.Hw Rough interface scattering
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Bi Mathematical theory of wave propagation
43.40.Ph Seismology and geophysical prospecting; seismographs

Sequential trans-dimensional Monte Carlo for range-dependent geoacoustic inversion

Jan Dettmer, Stan E. Dosso, and Charles W. Holland

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1794-1806 (2011); (13 pages) | Cited 2 times

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This paper develops a sequential trans-dimensional Monte Carlo algorithm for geoacoustic inversion in a strongly range-dependent environment. The algorithm applies advanced Markov chain Monte Carlo methods in combination with sequential techniques (particle filters) to carry out geoacoustic inversions for consecutive data sets acquired along a track. Changes in model parametrization along the track (e.g., number of sediment layers) are accounted for with trans-dimensional partition modeling, which intrinsically determines the amount of structure supported by the data information content. Challenging issues of rapid environmental change between consecutive data sets and high information content (peaked likelihood) are addressed by bridging distributions implemented using annealed importance sampling. This provides an efficient method to locate high-likelihood regions for new data which are distant and/or disjoint from previous high-likelihood regions. The algorithm is applied to simulated reflection-coefficient data along a track, such as can be collected using a towed array close to the seabed. The simulated environment varies rapidly along the track, with changes in the number of layers, layer thicknesses, and geoacoustic parameters within layers. In addition, the seabed contains a geologic fault, where all layers are offset abruptly, and an erosional channel. Changes in noise level are also considered.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.60.Pt Signal processing techniques for acoustic inverse problems
43.60.Wy Non-stationary signal analysis, non-linear systems, and higher order statistics

The energy ratio mapping algorithm: A tool to improve the energy-based detection of odontocete echolocation clicks

Holger Klinck and David K. Mellinger

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1807-1812 (2011); (6 pages) | Cited 1 time

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The energy ratio mapping algorithm (ERMA) was developed to improve the performance of energy-based detection of odontocete echolocation clicks, especially for application in environments with limited computational power and energy such as acoustic gliders. ERMA systematically evaluates many frequency bands for energy ratio-based detection of echolocation clicks produced by a target species in the presence of the species mix in a given geographic area. To evaluate the performance of ERMA, a Teager-Kaiser energy operator was applied to the series of energy ratios as derived by ERMA. A noise-adaptive threshold was then applied to the Teager-Kaiser function to identify clicks in data sets. The method was tested for detecting clicks of Blainville’s beaked whales while rejecting echolocation clicks of Risso’s dolphins and pilot whales. Results showed that the ERMA-based detector correctly identified 81.6% of the beaked whale clicks in an extended evaluation data set. Average false-positive detection rate was 6.3% (3.4% for Risso’s dolphins and 2.9% for pilot whales).
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43.30.Sf Acoustical detection of marine life; passive and active
43.80.Ev Acoustical measurement methods in biological systems and media

A waveguide invariant adaptive matched filter for active sonar target depth classification

Ryan Goldhahn, Granger Hickman, and Jeffrey Krolik

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1813-1824 (2011); (12 pages)

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This paper addresses depth discrimination of a water column target from bottom clutter discretes in wideband active sonar. To facilitate classification, the waveguide invariant property is used to derive multiple snapshots by uniformly sub-sampling the short-time Fourier transform (STFT) coefficients of a single ping of wideband active sonar data. The sub-sampled target snapshots are used to define a waveguide invariant spectral density matrix (WI-SDM), which allows the application of adaptive matched-filtering based approaches for target depth classification. Depth classification is achieved using a waveguide invariant minimum variance filter (WI-MVF) which matches the observed WI-SDM to depth-dependent signal replica vectors generated from a normal mode model. Robustness to environmental mismatch is achieved by adding environmental perturbation constraints (EPC) derived from signal covariance matrices averaged over the uncertain channel parameters. Simulation and real data results from the SCARAB98 and CLUTTER09 experiments in the Mediterranean Sea are presented to illustrate the approach. Receiver operating characteristics (ROC) for robust waveguide invariant depth classification approaches are presented which illustrate performance under uncertain environmental conditions.
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43.30.Vh Active sonar systems
43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.60.Uv Model-based signal processing

Ocean bottom profiling with ambient noise: A model for the passive fathometer

James Traer, Peter Gerstoft, and William S. Hodgkiss

J. Acoust. Soc. Am. Volume 129, Issue 4, pp. 1825-1836 (2011); (12 pages) | Cited 4 times

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A model is presented for the complete passive fathometer response to ocean surface noise, interfering discrete noise sources, and locally uncorrelated noise in an ideal waveguide. The leading order term of the ocean surface noise contribution produces the cross-correlation of vertical multipaths and yields the depth of sub-bottom reflectors. Discrete noise incident on the array via multipaths give multiple peaks in the fathometer response. These peaks may obscure the sub-bottom reflections but can be attenuated with use of minimum variance distortionless response (MVDR) steering vectors. The seabed critical angle introduces discontinuities in the spatial distribution of distant surface noise and may introduce spurious peaks in the passive fathometer response. These peaks can be attenuated by beamforming within a bandwidth limited by the array geometry and critical angle.
Show PACS
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.60.Pt Signal processing techniques for acoustic inverse problems
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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