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Journal of the Acoustical Society of America

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Dec 2011

Volume 130, Issue 6, pp. EL373-4184

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Asymmetric glottal jet deflection: Differences of two- and three-dimensional models

Willy Mattheus and Christoph Brücker

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL373-EL379 (2011); (7 pages)

Online Publication Date: 10 Nov 2011

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Flow is studied through a channel with an oscillating orifice mimicking the motion of the glottal-gap during phonation. Simulations with prescribed flow and wall-motion are carried out for different orifice geometries, a 2D slit-like and a 3D lens-like one. Although the jet emerges from a symmetric orifice a significant deflection occurs in case of the slit-like geometry, contrary to the 3D lens-like one. The results demonstrate the dependency of jet entrainment and vortex dynamics on the orifice geometry and the interpretation of asymmetric jet deflection with regard to the relevance of the Coanda effect in the process of human phonation.
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43.70.Bk Models and theories of speech production
43.70.Aj Anatomy and physiology of the vocal tract, speech aerodynamics, auditory kinetics
43.70.Jt Instrumentation and methodology for speech production research
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A connectionist study on the role of pitch in infant-directed speech

Bruno Gauthier and Rushen Shi

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL380-EL386 (2011); (7 pages)

Online Publication Date: 10 Nov 2011

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Infant-directed speech (IDS) is believed to facilitate language learning. However, the benefit may be either due to clearer acoustic correlates to linguistic structures, or simply increased attention from infants induced by IDS exaggerated prosody. This study investigated the pure effect of IDS pitch on lexical tone learning, with attentional/affective factors removed by using artificial neural networks. Following training with the pitch of Mandarin tones in IDS versus adult-directed speech, the networks yielded equal tonal categorization for both registers. IDS pitch produced no additional linguistic support. IDS pitch appears to strictly play the non-linguistic role of attention/affect, which may indirectly benefit learning.
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43.71.Ft Development of speech perception
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Design and implementation of a shielded underwater vector sensor for laboratory environments

Andrew R. Barnard and Stephen A. Hambric

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL387-EL391 (2011); (5 pages)

Online Publication Date: 10 Nov 2011

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Underwater acoustic vector sensors, for measuring acoustic intensity, are typically used in open water where electromagnetic interference (EMI) is generally not a contributor to overall background noise. However, vector sensors are also useful in a laboratory setting where EMI can be a limiting factor at low frequencies. An underwater vector sensor is designed and built with specific care for EMI immunity. The sensor, and associated signal processing, is shown to reduce background noise at EMI frequencies by 10–50 dB and 10–20 dB across the entire frequency bandwidth, as compared to an identical unshielded vector sensor.
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43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.58.Dj Sound velocity
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Low latency localization of multiple sound sources in reverberant environments

Marko Ðurković, Tim Habigt, Martin Rothbucher, and Klaus Diepold

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL392-EL398 (2011); (7 pages)

Online Publication Date: 10 Nov 2011

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Sound source localization algorithms determine the physical position of a sound source in respect to a listener. For practical applications, a localization algorithm design has to take into account real world conditions like multiple active sources, reverberation, and noise. The application can impose additional constraints on the algorithm, e.g., a requirement for low latency. This work defines the most important constraints for practical applications, introduces an algorithm, which tries to fulfill all requirements as good as possible, and compares it to state-of-the-art sound source localization approaches.
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43.60.Jn Source localization and parameter estimation
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Correlations of group velocity, phase velocity, and dispersion with bone density in bovine trabecular bone

Kang Il Lee

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL399-EL404 (2011); (6 pages) | Cited 1 time

Online Publication Date: 15 Nov 2011

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The present study investigated the correlations of the group velocity, the phase velocity, and the velocity dispersion with the apparent bone density in bovine trabecular bone in vitro. The phase velocity exhibited the negative dispersion, consistent with the behavior in human trabecular bone. The group and the phase velocities were found to increase with increasing apparent bone density, respectively, exhibiting similar high correlations of r = 0.94 and 0.96. The negative dispersion rate exhibited a decreasing dependence on the apparent bone density, with a significant correlation of r = −0.86.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.80.Qf Medical diagnosis with acoustics
43.80.Vj Acoustical medical instrumentation and measurement techniques
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Experimental verification of subwavelength acoustic focusing using a near-field array of closely spaced elements

Reza Abasi, Loïc Markley, and George V. Eleftheriades

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. EL405-EL409 (2011); (5 pages)

Online Publication Date: 18 Nov 2011

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A linear array of closely spaced sound transducers is presented that can produce a subwavelength-focused intensity profile at a distance of a quarter wavelength. This work is related to research on super-resolution using metamaterials in both the acoustic and optical domains. It is designed using the principle of shifted beams, a near-field antenna array theory developed for the subwavelength focusing of electromagnetic waves. Once the spatial sound pattern is characterized for each source, the optimal weights for a minimum beam width can be calculated. An experiment operating at 4 kHz was able to successfully construct a super-focused beam.
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43.20.Bi Mathematical theory of wave propagation
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
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An expression for the radiation force exerted by an acoustic beam with arbitrary wavefront (L)

Glauber T. Silva

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3541-3544 (2011); (4 pages) | Cited 1 time

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Most studies investigating the acoustic radiation force upon a target are based on symmetry considerations between the object and the incident beam. Even so, this symmetry condition is not always fulfilled in several cases. An expression for the radiation force is obtained as a function of the beam-shape and the scattering coefficients of an incident wave and the object, respectively. The expression for the radiation force caused by a plane wave on a rigid sphere is used to validate the formula. This method represents a theoretical advance permitting different interpretations and predictions concerned to the acoustic radiation force phenomenon.
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43.25.Qp Radiation pressure
43.20.Fn Scattering of acoustic waves
43.20.El Reflection, refraction, diffraction of acoustic waves

An exact method of regularity analysis for auditory brainstem neurons (L)

M. C. M. Wright, S. Bleeck, and I. M. Winter

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3545-3548 (2011); (4 pages)

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The standard regularity analysis for spike trains in cochlear nucleus neurons evoked by tonebursts first proposed by Bourk is widely used, primarily as one of the criteria for classification of such neurons. It is shown that this procedure does not estimate quite what it is supposed to, and introduces unnecessary noise to its results due to its use of bins. Instead the desired quantities (mean and coefficient of variation of the lengths of all inter-spike intervals in progress as a function of time since stimulus onset) can all be exactly calculated directly from the spike train without the need for data binning. The implications for classification and other studies are discussed.
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43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Ri Evoked responses to sounds
43.64.Yp Instruments and methods

Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L)

Ivan Z. Nenadic, Matthew W. Urban, Miguel Bernal, and James F. Greenleaf

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3549-3552 (2011); (4 pages)

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In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb–Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb–Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb–Rayleigh attenuation. Results of numerical simulations in the frequency range 0–500 Hz are presented.
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43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues
43.20.Bi Mathematical theory of wave propagation
43.20.Jr Velocity and attenuation of elastic and poroelastic waves
43.20.Mv Waveguides, wave propagation in tubes and ducts

Evaluation of the effective speed of sound in phononic crystals by the monodromy matrix method (L)

A. A. Kutsenko, A. L. Shuvalov, and A. N. Norris

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3553-3557 (2011); (5 pages)

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A scheme for evaluating the effective quasistatic speed of sound c in two- and three-dimensional periodic materials is reported. The approach uses a monodromy-matrix operator to enable direct integration in one of the coordinates and exponentially fast convergence in others. As a result, the solution for c has a more closed form than previous formulas. It significantly improves the efficiency and accuracy of evaluating c for high-contrast composites as demonstrated by a two-dimensional scalar-wave example with extreme behavior.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Hq Velocity and attenuation of acoustic waves

Observation of traveling thermoacoustic shock waves (L)

Tetsushi Biwa, Takuma Takahashi, and Taichi Yazaki

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3558-3561 (2011); (4 pages)

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Shock waves were explored in the thermoacoustic spontaneous gas oscillations occurring in a gas column with a steep temperature gradient. The results show that a periodic shock occurs in the traveling wave mode in a looped tube but not in the standing wave mode in a resonator. Measurements of the harmonic components of the acoustic intensity reveal a clear difference between them. The temperature gradient acts as an acoustic energy source for the harmonic components of the shock wave in the traveling wave mode but as an acoustic energy sink of the second harmonic in the standing wave mode.
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43.25.Cb Macrosonic propagation, finite amplitude sound; shock waves
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Influence of pitch, timbre and timing cues on melodic contour identification with a competing masker (L)

Meimei Zhu, Bing Chen, John J. Galvin, and Qian-Jie Fu

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3562-3565 (2011); (4 pages)

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Pitch, timbre, and/or timing cues may be used to stream and segregate competing musical melodies and instruments. In this study, melodic contour identification was measured in cochlear implant (CI) and normal-hearing (NH) listeners, with and without a competing masker; timing, pitch, and timbre cues were varied between the masker and target contour. NH performance was near-perfect across different conditions. CI performance was significantly poorer than that of NH listeners. While some CI subjects were able to use or combine timing, pitch and/or timbre cues, most were not, reflecting poor segregation due to poor spectral resolution.
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43.66.Jh Timbre, timbre in musical acoustics
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ts Auditory prostheses, hearing aids
43.64.Me Effects of electrical stimulation, cochlear implant
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Localization of a small change in a multiple scattering environment without modeling of the actual medium

S. T. Rakotonarivo, S. C. Walker, W. A. Kuperman, and P. Roux

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3566-3573 (2011); (8 pages)

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A method to actively localize a small perturbation in a multiple scattering medium using a collection of remote acoustic sensors is presented. The approach requires only minimal modeling and no knowledge of the scatterer distribution and properties of the scattering medium and the perturbation. The medium is ensonified before and after a perturbation is introduced. The coherent difference between the measured signals then reveals all field components that have interacted with the perturbation. A simple single scatter filter (that ignores the presence of the medium scatterers) is matched to the earliest change of the coherent difference to localize the perturbation. Using a multi-source/receiver laboratory setup in air, the technique has been successfully tested with experimental data at frequencies varying from 30 to 60 kHz (wavelength ranging from 0.5 to 1 cm) for cm-scale scatterers in a scattering medium with a size two to five times bigger than its transport mean free path.
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43.20.Gp Reflection, refraction, diffraction, interference, and scattering of elastic and poroelastic waves
43.20.Fn Scattering of acoustic waves

Impact of attenuation on guided mode wavenumber measurement in axial transmission on bone mimicking plates

Jean-Gabriel Minonzio, Josquin Foiret, Maryline Talmant, and Pascal Laugier

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3574-3582 (2011); (9 pages) | Cited 1 time

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Robust signal processing methods adapted to clinical measurements of guided modes are required to assess bone properties such as cortical thickness and porosity. Recently, an approach based on the singular value decomposition (SVD) of multidimensional signals recorded with an axial transmission array of emitters and receivers has been proposed for materials with negligible absorption, see Minonzio et al. [J. Acoust. Soc. Am. 127, 2913–2919 (2010)]. In presence of absorption, the ability to extract guided mode degrades. The objective of the present study is to extend the method to the case of absorbing media, considering attenuated plane waves (complex wavenumber). The guided mode wavenumber extraction is enhanced and the order of magnitude of the attenuation of the guided mode is estimated. Experiments have been carried out on 2 mm thick plates in the 0.2–2 MHz bandwidth. Two materials are inspected: polymethylacrylate (PMMA) (isotropic with absorption) and artificial composite bones (Sawbones, Pacific Research Laboratory Inc, Vashon, WA) which is a transverse isotropic absorbing medium. Bulk wave velocities and bulk attenuation have been evaluated from transmission measurements. These values were used to compute theoretical Lamb mode wavenumbers which are consistent with the experimental ones obtained with the SVD-based approach.
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43.20.Ye Measurement methods and instrumentation
43.80.Vj Acoustical medical instrumentation and measurement techniques
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.60.Fg Acoustic array systems and processing, beam-forming
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Nonlinear elastodynamics in micro-inhomogeneous solids observed by head-wave based dynamic acoustoelastic testing

G. Renaud, M. Talmant, S. Callé, M. Defontaine, and P. Laugier

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3583-3589 (2011); (7 pages)

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Dynamic acoustoelastic testing provides a more complete insight into the acoustic nonlinearity exhibited by micro-inhomogeneous media like granular and cracked materials. This method consists of measuring time of flight and energy modulations of pulsed ultrasonic waves induced by a low-frequency standing wave. Here pulsed ultrasonic head waves were employed to assess elastic and dissipative nonlinearities in a region near the surface of a solid. Synchronization of the ultrasound pulse sequence with the low-frequency excitation provided instantaneous variations in the elastic modulus and the attenuation as functions of the instantaneous low-frequency strain. Weak quadratic elastic nonlinearity and no dissipative nonlinearity were detected in duralumin. In limestone, distinction between tensile and compressive behaviors revealed an asymmetry in the acoustic nonlinearity and hysteresis in both the elastic modulus and the attenuation variations. Measured nonlinear acoustical parameters are in good agreement with values obtained by different techniques. Reversible acoustically induced conditioning modified the acoustic nonlinearity both quantitatively and qualitatively. It reduced tension-compression asymmetry, suggesting a nonequilibrium modification of the sources of acoustic nonlinearity. Additionally to the metrology of the acoustic nonlinearity, head wave based dynamic acoustoelastic testing may be a useful tool to monitor changes in the microstructure or the accumulation of damage in solids.
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43.25.Ed Effect of nonlinearity on velocity and attenuation
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.25.Dc Nonlinear acoustics of solids
43.25.Ba Parameters of nonlinearity of the medium
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Improved prediction of the turbulence-shear contribution to wind noise pressure spectra

Jiao Yu, Richard Raspet, Jeremy Webster, and JohnPaul Abbott

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3590-3594 (2011); (5 pages)

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In previous research [Raspet et al., J. Acoust. Soc. Am. 123(3), 1260–1269 (2008)], predictions of the low frequency turbulence-turbulence and turbulence-mean shear interaction pressure spectra measured by a large wind screen were developed and compared to the spectra measured using large spherical wind screens in the flow. The predictions and measurements agreed well except at very low frequencies where the turbulence-mean shear contribution dominated the turbulence-turbulence interaction pressure. In this region the predicted turbulence-mean shear interaction pressure did not show consistent agreement with microphone measurements. The predicted levels were often much larger than the measured results. This paper applies methods developed to predict the turbulence-shear interaction pressure measured at the ground [Yu et al., J. Acoust. Soc. Am. 129(2), 622–632 (2011)] to improve the prediction of the turbulence-shear interaction pressure above the ground surface by incorporating a realistic wind velocity profile and realistic turbulence anisotropy. The revised prediction of the turbulence-shear interaction pressure spectra compares favorably with wind-screen microphone measurements in large wind screens at low frequency.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields

Random focusing of nonlinear acoustic N-waves in fully developed turbulence: Laboratory scale experiment

Mikhail Averiyanov, Sébastien Ollivier, Vera Khokhlova, and Philippe Blanc-Benon

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3595-3607 (2011); (13 pages)

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A laboratory experiment was conducted to study the propagation of short duration (25 μs) and high amplitude (1000 Pa) acoustic N-waves in turbulent flow. Turbulent flows with a root-mean-square value of the fluctuating velocity up to 4 m/s were generated using a bidimensional nozzle (140 × 1600 mm2). Energy spectra of velocity fluctuations were measured and found in good agreement with the modified von Kármán spectrum for fully developed turbulence. Spherical N-waves were generated by an electric spark source. Distorted waves were measured by four 3 mm diameter microphones placed beyond the turbulent jet. The presence of turbulence resulted in random focusing of the pulse; more than a threefold increase of peak pressures was occasionally observed. Statistics of the acoustic field parameters were evaluated as functions of the propagation distance and the level of turbulence fluctuations. It is shown that random inhomogeneities decrease the mean peak positive pressure up to 30% at 2 m from the source, double the mean rise time, and cause the arrival time about 0.3% earlier than that for corresponding conditions in still air. Probability distributions of the pressure amplitude possess autosimilarity properties with respect to the level of turbulence fluctuations.
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43.28.Gq Outdoor sound propagation and scattering in a turbulent atmosphere, and in non-uniform flow fields
43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves
43.28.Mw Shock and blast waves, sonic boom

Incorporating source directionality into outdoor sound propagation calculations

Sergey N. Vecherin, D. Keith Wilson, and Vladimir E. Ostashev

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3608-3622 (2011); (15 pages) | Cited 2 times

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Many outdoor sound sources, such as aircraft or ground vehicles, exhibit directional radiation patterns. However, long-range sound propagation algorithms are usually formulated for omnidirectional point sources. This paper describes two methods for incorporating directional sources into long-range sound propagation algorithms. The first is the equivalent source method (ESM), which determines a compact distribution of omnidirectional point sources reproducing a given directivity pattern in the far field. This method can be used with any propagation algorithm because it explicitly reconstructs a source function as a set of point sources with certain amplitudes and positions. The second is a directional starter method (DSM), which is developed specifically for the parabolic equation (PE) algorithms. This method derives narrow- or wide-angle directional starter fields, corresponding to a given source directivity pattern, without reconstructing the equivalent source distribution. Although the ESM can also be used for the PE, the DSM is simpler and can be more convenient, especially if the sound propagation is calculated only for one or a few azimuthal directions. While these two methods are found to produce generally distinct starter fields, they nonetheless yield identical directivity patterns.
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43.28.Hr Outdoor sound sources
43.28.Js Numerical models for outdoor propagation
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Model-based seafloor characterization employing multi-beam angular backscatter data—A comparative study with dual-frequency single beam

K. Haris, Bishwajit Chakraborty, Chanchal De, R. G. Prabhudesai, and William Fernandes

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3623-3632 (2011); (10 pages)

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Sediment geoacoustic inversion results are estimated employing a multi-beam (MB) echo-sounding system operable at 95 kHz. To characterize the western continental shelf of India (off Goa) seafloor, MB backscatter signals were acquired along with grab sediment samples. The substrate type and roughness of the site were estimated using the composite roughness scattering model with the measured backscatter values. The seafloor parameters, namely mean grain size (Mϕ); roughness spectrum strength (w2) and exponent (γ2); and sediment volume parameter (σ2), for coarse and fine grain sediments are estimated by employing the MB system. These parameters have also been estimated at two other frequencies (33 and 210 kHz) and are compared to the ground truth data to provide sufficient support in validating the model results and increasing the understanding of the shelf seafloor processes. Distinct interclass separations between the sediment provinces are evident from the estimated mean grain size Mϕ and water-sediment interface roughness w2. The seafloor parameters for coarse and fine grain sediments derived from the 95 kHz MB data are consistent with the sediment sample data as well as with the inversion results obtained using backscatter data at 33 and 210 kHz from the same locations.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography

Coherent averaging of the passive fathometer response using short correlation time

James Traer and Peter Gerstoft

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3633-3641 (2011); (9 pages)

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The passive fathometer algorithm was applied to data from two drifting array experiments in the Mediterranean, Boundary 2003 and 2004. The passive fathometer response was computed with correlation times from 0.34 to 90 s and, for correlation times less than a few seconds, the observed signal-to-noise ratio (SNR) agrees with a 1D model of SNR of the passive fathometer response in an ideal waveguide. In the 2004 experiment, the fathometer response showed the array depth varied periodically with an amplitude of 1 m and a period of 7 s consistent with wave driven motion of the array. This introduced a destructive interference, which prevents the SNR growing with increasing correlation time. A peak-tracking algorithm applied to the fathometer response of experimental data was used to remove this motion allowing the coherent passive fathometer response to be averaged over several minutes without destructive interference. Multirate adaptive beamforming, using 90 s correlation time to form adaptive steer vectors which were applied to 0.34 s data snapshots, increases the SNR of the passive fathometer response.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Wi Passive sonar systems and algorithms, matched field processing in underwater acoustics
43.30.Xm Underwater measurement and calibration instrumentation and procedures

Where the ocean influences the impulse response and its effect on synchronous changes of acoustic travel time

John L. Spiesberger

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3642-3650 (2011); (9 pages)

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In 1983, sounds at 133 Hz, 0.06 s resolution were transmitted in the Pacific for five days at 2 min intervals over 3709 km between bottom-mounted instruments maintained with atomic clocks. In 1989, a technique was developed to measure changes in acoustic travel time with an accuracy of 135 microseconds at 2 min intervals for selected windows of travel time within the impulse response. The data have short-lived 1 to 10 ms oscillations of travel time with periods less than a few days. Excluding tidal effects, different windows exhibited significant synchronized changes in travel time for periods shorter than 10 h. In the 1980s, this phenomenon was not understood because internal waves have correlation lengths of a few kilometers which are smaller than the way sound was thought to sample the ocean along well-separated and distinct rays corresponding to different windows. The paradox’s resolution comes from modern theories that replace the ray-picture with finite wavelength representations that predict sound can be influenced in the upper ocean over horizontal scales such as 20 km or more. Thus, different windows are influenced by the same short-scale fluctuations of sound speed. This conclusion is supported by the data and numerical simulations of the impulse response.
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43.30.Re Signal coherence or fluctuation due to sound propagation/scattering in the ocean
43.30.Cq Ray propagation of sound in water
43.30.Qd Global scale acoustics; ocean basin thermometry, transbasin acoustics

Vocal characteristics of pygmy blue whales and their change over time

Alexander N. Gavrilov, Robert D. McCauley, Chandra Salgado-Kent, Joy Tripovich, and Chris Burton

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3651-3660 (2011); (10 pages)

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Vocal characteristics of pygmy blue whales of the eastern Indian Ocean population were analyzed using data from a hydroacoustic station deployed off Cape Leeuwin in Western Australia as part of the Comprehensive Nuclear-Test-Ban Treaty monitoring network, from two acoustic observatories of the Australian Integrated Marine Observing System, and from individual sea noise loggers deployed in the Perth Canyon. These data have been collected from 2002 to 2010, inclusively. It is shown that the themes of pygmy blue whale songs consist of ether three or two repeating tonal sounds with harmonics. The most intense sound of the tonal theme was estimated to correspond to a source level of 179 ± 2 dB re 1 μPa at 1 m measured for 120 calls from seven different animals. Short-duration calls of impulsive downswept sound from pygmy blue whales were weaker with the source level estimated to vary between 168 to 176 dB. A gradual decrease in the call frequency with a mean rate estimated to be 0.35 ± 0.3 Hz/year was observed over nine years in the frequency of the third harmonic of tonal sound 2 in the whale song theme, which corresponds to a negative trend of about 0.12 Hz/year in the call fundamental frequency.
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43.30.Sf Acoustical detection of marine life; passive and active
43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
43.30.Nb Noise in water; generation mechanisms and characteristics of the field

A threatened beluga (Delphinapterus leucas) population in the traffic lane: Vessel-generated noise characteristics of the Saguenay-St. Lawrence Marine Park, Canada

Ian H. McQuinn, Véronique Lesage, Dominic Carrier, Geneviève Larrivée, Yves Samson, Sylvain Chartrand, Robert Michaud, and James Theriault

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3661-3673 (2011); (13 pages)

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The threatened resident beluga population of the St. Lawrence Estuary shares the Saguenay-St. Lawrence Marine Park with significant anthropogenic noise sources, including marine commercial traffic and a well-established, vessel-based whale-watching industry. Frequency-dependent (FD) weighting was used to approximate beluga hearing sensitivity to determine how noise exposure varied in time and space at six sites of high beluga summer residency. The relative contribution of each source to acoustic habitat degradation was estimated by measuring noise levels throughout the summer and noise signatures of typical vessel classes with respect to traffic volume and sound propagation characteristics. Rigid-hulled inflatable boats were the dominant noise source with respect to estimated beluga hearing sensitivity in the studied habitats due to their high occurrence and proximity, high correlation with site-specific FD-weighted sound levels, and the dominance of mid-frequencies (0.3–23 kHz) in their noise signatures. Median C-weighted sound pressure level (SPLRMS) had a range of 19 dB re 1 μPa between the noisiest and quietest sites. Broadband SPLRMS exceeded 120 dB re 1 μPa 8–32% of the time depending on the site. Impacts of these noise levels on St. Lawrence beluga will depend on exposure recurrence and individual responsiveness.
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43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
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Generalized optical theorems for the reconstruction of Green’s function of an inhomogeneous elastic medium

Ludovic Margerin and Haruo Sato

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3674-3690 (2011); (17 pages) | Cited 1 time

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This paper investigates the reconstruction of elastic Green’s function from the cross-correlation of waves excited by random noise in the context of scattering theory. Using a general operator equation—the resolvent formula—Green’s function reconstruction is established when the noise sources satisfy an equipartition condition. In an inhomogeneous medium, the operator formalism leads to generalized forms of optical theorem involving the off-shell T-matrix of elastic waves, which describes scattering in the near-field. The role of temporal absorption in the formulation of the theorem is discussed. Previously established symmetry and reciprocity relations involving the on-shell T-matrix are recovered in the usual far-field and infinitesimal absorption limits. The theory is applied to a point scattering model for elastic waves. The T-matrix of the point scatterer incorporating all recurrent scattering loops is obtained by a regularization procedure. The physical significance of the point scatterer is discussed. In particular this model satisfies the off-shell version of the generalized optical theorem. The link between equipartition and Green’s function reconstruction in a scattering medium is discussed.
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43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
43.20.Bi Mathematical theory of wave propagation
43.40.Ph Seismology and geophysical prospecting; seismographs

Effect of laser beam incidence angle on the thermoelastic generation in semi-transparent materials

Samuel Raetz, Thomas Dehoux, and Bertrand Audoin

J. Acoust. Soc. Am. Volume 130, Issue 6, pp. 3691-3697 (2011); (7 pages)

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When a laser beam is absorbed in a semi-transparent material, a volume acoustic source is created owing to penetration of the laser beam inside the material and to thermoelastic transduction. Many experimental and theoretical studies have been conducted to better understand this ultrasound generation process with normal laser light incidence on the material surface. The purpose of this paper is to analyze the effects of the asymmetry caused by oblique incidence of a laser line source on the generation of acoustic waves in semi-transparent isotropic materials. Experiments on a glass plate demonstrate that such an obliquely incident laser light strongly affects bulk acoustic waves generation. Compressional and shear waves are enhanced and the loss of symmetry of the acoustic source causes asymmetrical behavior of the acoustic waves. Surprisingly, compressional-wave amplitude decreases whereas shear-wave amplitude increases in the region where the electromagnetic energy is refracted. This feature is explained by semi-analytical calculations.
Show PACS
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.38.Zp Acoustooptic and photoacoustic transducers
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants
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