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Jan 2012

Volume 131, Issue 1, pp. EL1-997

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Analytical study of the horizontal ducting of sound by an oceanic front over a slope

Ying-Tsong Lin and James F. Lynch

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL1-EL7 (2011); (7 pages)

Online Publication Date: 13 Dec 2011

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The horizontal ducting of sound by an oceanic temperature front over a sloping bottom is studied with an idealized wedge model consisting of a lateral interface across the slope. The water outside the frontal interface has higher temperature, hence faster sound speed, and it will produce inshore reflection/refraction of the sound. Combining the offshore refraction caused by the sloping bottom, propagating sound can be ducted along the front. An analytical solution to the sound pressure field in the idealized model is derived, and an example is presented to demonstrate and discuss the ducting effect.
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43.30.Bp Normal mode propagation of sound in water
43.20.Bi Mathematical theory of wave propagation
43.20.Mv Waveguides, wave propagation in tubes and ducts
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Toward an objective measure for a “stream segregation” task

Virginia M. Richards, Eva Maria Carreira, and Yi Shen

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL8-EL13 (2011); (6 pages)

Online Publication Date: 13 Dec 2011

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A procedure to estimate the relative contribution of “A” and “B” tones for a stream-segregation task is described. Listeners detected a delay in the penultimate A tone in an A-B-A-B sequence of tones. For small A-B frequency separations, for most listeners, classification models based on both the A and B tones were superior to models based on just the A tones. For large frequency separations, models based on just the A tones were superior, indicating the A and B tones were segregated. The results also revealed individual differences in the strategies adopted to complete the task.
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43.66.Lj Perceptual effects of sound
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
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Using practical supergain for passive imaging with noise

Martin Siderius

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL14-EL20 (2011); (7 pages) | Cited 1 time

Online Publication Date: 13 Dec 2011

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Recent work has shown that endfire beamforming of ocean noise can be used to produce images of the seabed layering [ Siderius et al., J. Acoust. Soc. Am. 120, 1315–1323 (2006)]. This initial noise imaging technique used conventional beamforming and was later extended to adaptive beamforming that is theoretically optimal. However, there can be problems with adaptive methods, which include extreme sensitivity to random errors, the required averaging time, and computational complexity. Here, the concept of supergain is used to show that delay and sum beamforming can produce nearly the same results as the optimal adaptive methods without the drawbacks.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
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
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A passive inverse filter for Green’s function retrieval

Thomas Gallot, Stefan Catheline, Philippe Roux, and Michel Campillo

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL21-EL27 (2011); (7 pages)

Online Publication Date: 13 Dec 2011

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Passive methods for the recovery of Green’s functions from ambient noise require strong hypotheses, including isotropic distribution of the noise sources. Very often, this distribution is nonisotropic, which introduces bias in the Green’s function reconstruction. To minimize this bias, a spatiotemporal inverse filter is proposed. The method is tested on a directive noise field computed from an experimental active seismic data set. The results indicate that the passive inverse filter allows the manipulation of the spatiotemporal degrees of freedom of a complex wave field, and it can efficiently compensate for the noise wavefield directivity.
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43.35.Pt Surface waves in solids and liquids
43.40.Ph Seismology and geophysical prospecting; seismographs
43.60.Tj Wave front reconstruction, acoustic time-reversal, and phase conjugation
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Phonemic restoration effect reversed in a reverberant room

Nirmal Kumar Srinivasan and Pavel Zahorik

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL28-EL34 (2011); (7 pages)

Online Publication Date: 13 Dec 2011

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Classic demonstrations of the phonemic restoration effect show increased intelligibility of interrupted speech when the interruptions are caused by a plausible masking sound rather than by silent periods. Previous studies of this effect have been conducted exclusively under anechoic or nearly anechoic listening conditions. This study demonstrates that the effect is reversed when sounds are presented in a realistically simulated reverberant room (broadband T60 = 1.1 s): intelligibility is greater for silent interruptions than for interruptions by unmodulated noise. Additional results suggest that the reversal is primarily due to filling silent intervals with reverberant energy from the speech signal.
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43.71.Gv Measures of speech perception (intelligibility and quality)
43.66.Lj Perceptual effects of sound
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Do male northern elephant seals recognize individuals or merely relative dominance rank?

Stephen J. Insley and Marla M. Holt

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL35-EL41 (2011); (7 pages)

Online Publication Date: 13 Dec 2011

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Vocal recognition was tested in a socially dynamic context where many individuals interact: the female defense polygyny practiced by male northern elephant seals. The goal was to tease apart whether animals recognize other individuals or instead use a simple rule-based category (i.e., relative dominance rank). A total of 67 playback experiments conducted with 18 males at Año Nuevo State Reserve, California, tested three aspects of recognition: (1) recognition of relative rank; (2) whether such recognition was continuous or categorical; and (3) recognition of familiarity. Results indicate that males recognize familiar individuals although responses are primarily based on relative dominance rank.
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43.66.Gf Detection and discrimination of sound by animals
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing
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Spectral integration versus multiple looks in the sample discrimination of intensity

Robert A. Lutfi and Lynn Gilbertson

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL42-EL47 (2011); (6 pages)

Online Publication Date: 13 Dec 2011

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A fundamental property of hearing is that signals become more detectable as their bandwidth is increased. Two models have been proposed to account for this result. The integration model assumes that detection is mediated by the output of a single frequency channel matched in bandwidth to the signal. The multiple-looks model assumes that detection is based on the combination of outputs from multiple channels matched to the individual frequencies of the signal. Results are reported supporting the integration model.
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43.66.Ba Models and theories of auditory processes
43.66.Fe Discrimination: intensity and frequency
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Sounds of Indo-Pacific humpback dolphins (Sousa chinensis) in West Hong Kong: A preliminary description

Paul Q. Sims, Robin Vaughn, Samuel K. Hung, and Bernd Würsig

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL48-EL53 (2011); (6 pages)

Online Publication Date: 13 Dec 2011

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Vocalizations of Indo-Pacific humpback dolphins (Sousa chinensis) in west Hong Kong waters were described from 12 recordings in 2010. A broadband hydrophone system recorded sounds. Vocalizations were characterized as broadband click trains, burst pulses, and narrowband frequency modulated sounds, including whistles generally similar to those of some other delphinid cetaceans. A comparison of results to previous humpback dolphin sound descriptions for Moreton Bay, Australia found broad similarities except for the apparent absence of “quacks” and “grunts” in the present study, which are of low frequency and thus were possibly masked by anthropogenic and other low frequency noise in the Hong Kong habitat.
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43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
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Acoustic scattering from density and sound speed gradients: Modeling of oceanic pycnoclines

Tetjana Ross and Andone C. Lavery

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL54-EL60 (2011); (7 pages)

Online Publication Date: 20 Dec 2011

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A weak-scattering model that allows prediction of acoustic scattering from oceanic pycnoclines (and the accompanying sound speed gradients) based on hydrographic profiles is described. Model predictions, based on profiles from four locations, indicate that scattering from oceanic pycnoclines is measurable using standard scientific sonars operating at frequencies up to 200 kHz but generally only for pycnocline thicknesses less than 10 m. Accurate scattering models are key to assessing whether acoustic remote sensing can be used to map oceanic pycnoclines and for determining whether scattering from pycnoclines needs to be taken into account when estimating, for instance, zooplankton abundance from acoustic data.
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43.30.Gv Backscattering, echoes, and reverberation in water due to combinations of boundaries
43.30.Ft Volume scattering
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Laboratory investigation of a passive acoustic method for measurement of underwater gas seep ebullition

Chad A. Greene and Preston S. Wilson

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL61-EL66 (2011); (6 pages)

Online Publication Date: 20 Dec 2011

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Passive acoustic techniques are of interest as a low-power means of quantifying underwater point-source gas ebullition. Toward the development of systems for logging natural seep activity, laboratory experiments were performed that exploited the bubble’s Minnaert natural frequency for the measurement of gas flow from a model seep. Results show agreement among acoustic, optical, and gas trap ebullition measurements over the range of emission rates from 0 to 10 bubbles per second. A mathematical model is proposed to account for the real gas behavior of bubbles which cannot be approximated as ideal, such as methane at marine depths exceeding 30 m.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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Frequency-dependent attenuation and backscatter coefficients in bovine trabecular bone from 0.2 to 1.2 MHz

Kang Il Lee and Min Joo Choi

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL67-EL73 (2011); (7 pages)

Online Publication Date: 20 Dec 2011

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The frequency-dependent attenuation and backscatter coefficients were measured in 25 bovine femoral trabecular bone samples from 0.2 to 1.2 MHz. When the average attenuation coefficient was fitted to a nonlinear power law α(f) = α0+α1fn, the exponent n was found to be 1.65. In contrast, the average backscatter coefficient was fitted to a power law η(f) = η1fn and the exponent n was measured as 3.25. The apparent bone density was significantly correlated with the parameter α1 (0.2–0.7 MHz: r = 0.852, 0.6–1.2 MHz: r = 0.832) as well as the backscatter coefficient (0.5 MHz: r = 0.751, 1.0 MHz: r = 0.808).
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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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Particle filtering for passive fathometer tracking

Zoi-Heleni Michalopoulou, Caglar Yardim, and Peter Gerstoft

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL74-EL80 (2011); (7 pages)

Online Publication Date: 23 Dec 2011

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Seabed interface depths and fathometer amplitudes are tracked for an unknown and changing number of sub-bottom reflectors. This is achieved by incorporating conventional and adaptive fathometer processors into sequential Monte Carlo methods for a moving vertical line array. Sediment layering information and time-varying fathometer response amplitudes are tracked by using a multiple model particle filter with an uncertain number of reflectors. Results are compared to a classical particle filter where the number of reflectors is considered to be known. Reflector tracking is demonstrated for both conventional and adaptive processing applied to the drifting array data from the Boundary 2003 experiment. The layering information is successfully tracked by the multiple model particle filter even for noisy fathometer outputs.
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43.60.Hj Time-frequency signal processing, wavelets
43.60.Jn Source localization and parameter estimation
43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
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Detection and location of cracks using loss of reciprocity in ultrasonic waves propagation

M. Scalerandi, A. S. Gliozzi, and C. L. E. Bruno

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. EL81-EL85 (2011); (5 pages)

Online Publication Date: 23 Dec 2011

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The reciprocity theorem is a general statement valid for elastic media, and it has been applied to the solution of elastic wave equations, transducers calibration, time reversal acoustics, etc. However, localized nonlinear scatterers are expected to break reciprocity even though the effect is, in several cases, negligible. Here the dependence of the reciprocity break on the presence of a localized damage and the influence of its relative position has been experimentally investigated. It will be shown that the break of reciprocity, usually considered a disadvantage, can be exploited as an imaging tool for localized cracks detection.
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43.25.-x Nonlinear acoustics
43.25.Dc Nonlinear acoustics of solids
43.60.Lq Acoustic imaging, displays, pattern recognition, feature extraction
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
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Giant strain-sensitivity of acoustic energy dissipation in solids containing dry and saturated cracks with wavy interfaces

V. Yu. Zaitsev and L. A. Matveev

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 1-12 (2012); (12 pages)

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Mechanisms of acoustic energy dissipation in heterogeneous solids attract much attention in view of their importance for material characterization, nondestructive testing, and geophysics. Due to the progress in measurement techniques in recent years, it has been revealed that rocks can demonstrate extremely high strain sensitivity of seismoacoustic loss. In particular, it has been found that strains of order 10-8 produced by lunar and solar tides are capable of causing variations in the seismoacoustic decrement on the order of several percent. Some laboratory data (although obtained for higher frequencies) also indicate the presence of very high dissipative nonlinearity. Conventionally discussed dissipation mechanisms (thermoelastic loss in dry solids, Biot and squirt-type loss in fluid-saturated ones) do not suffice to interpret such data. Here the dissipation at individual cracks is revised taking into account the influence of wavy asperities of their surfaces quite typical of real cracks, which can drastically change the values of the relaxation frequencies and can result in giant strain sensitivity of the dissipation without the necessity of assuming the presence of unrealistically thin (and, therefore, unrealistically soft) cracks. In particular, these mechanisms suggest interpretation for observations of pronounced amplitude modulation of seismo-acoustic waves by tidal strains.
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43.25.Ba Parameters of nonlinearity of the medium
43.25.Dc Nonlinear acoustics of solids
43.25.Ed Effect of nonlinearity on velocity and attenuation

Acoustic streaming field structure. Part II. Examples that include boundary-driven flow

Charles Bradley

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 13-23 (2012); (11 pages)

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In this paper three simple acoustic streaming problems are presented and solved. The purpose of the paper is to demonstrate the use of a previously published streaming model by Bradley [J. Acoust. Soc. Am. 100(3), 1399–1408 (1996)] and illustrate, with concrete examples, some of the features of streaming flows that were predicted by the general model. In particular, the problems are intended to demonstrate cases in which the streaming field boundary condition at the face of the radiator has a nontrivial lateral dc velocity component. Such a boundary condition drives a steady solenoidal flow just like a laterally translating boundary drives Couette flow.
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43.25.Nm Acoustic streaming

Stability analysis of ultrasound thick-shell contrast agents

Xiaozhen Lu, Georges L. Chahine, and Chao-Tsung Hsiao

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 24-34 (2012); (11 pages)

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The stability of thick shell encapsulated bubbles is studied analytically. 3-D small perturbations are introduced to the spherical oscillations of a contrast agent bubble in response to a sinusoidal acoustic field with different amplitudes of excitation. The equations of the perturbation amplitudes are derived using asymptotic expansions and linear stability analysis is then applied to the resulting differential equations. The stability of the encapsulated microbubbles to nonspherical small perturbations is examined by solving an eigenvalue problem. The approach then identifies the fastest growing perturbations which could lead to the breakup of the encapsulated microbubble or contrast agent.
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43.25.Yw Nonlinear acoustics of bubbly liquids
43.35.Wa Biological effects of ultrasound, ultrasonic tomography
43.80.Gx Mechanisms of action of acoustic energy on biological systems: physical processes, sites of action
43.80.Qf Medical diagnosis with acoustics
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Topographic effects on infrasound propagation

Mihan H. McKenna, Robert G. Gibson, Bob E. Walker, Jason McKenna, Nathan W. Winslow, and Aaron S. Kofford

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 35-46 (2012); (12 pages)

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Infrasound data were collected using portable arrays in a region of variable terrain elevation to quantify the effects of topography on observed signal amplitude and waveform features at distances less than 25 km from partially contained explosive sources during the Frozen Rock Experiment (FRE) in 2006. Observed infrasound signals varied in amplitude and waveform complexity, indicating propagation effects that are due in part to repeated local maxima and minima in the topography on the scale of the dominant wavelengths of the observed data. Numerical simulations using an empirically derived pressure source function combining published FRE accelerometer data and historical data from Project ESSEX, a time-domain parabolic equation model that accounted for local terrain elevation through terrain-masking, and local meteorological atmospheric profiles were able to explain some but not all of the observed signal features. Specifically, the simulations matched the timing of the observed infrasound signals but underestimated the waveform amplitude observed behind terrain features, suggesting complex scattering and absorption of energy associated with variable topography influences infrasonic energy more than previously observed.
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43.28.Dm Infrasound and acoustic-gravity waves
43.28.En Interaction of sound with ground surfaces, ground cover and topography, acoustic impedance of outdoor surfaces
43.60.Bf Acoustic signal detection and classification, applications to control systems
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Subcritical penetration of acoustic waves into inhomogenous seafloors

Linhui Peng and Gaokun Yu

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 47-53 (2012); (7 pages)

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A generalized model is applied to estimate the incoherent penetration ratio caused by volume scattering at grazing angles below the critical grazing angle. The factors that affect volume scattering have been discussed using experimental data in literature. A two-layered model that refers to sound scattering in two-layered media is used to evaluate the incoherent penetration ratio for most typical sediments. But for special cases, such as the experiment, SAX04, a three-layered model is necessary to describe scattering features especially for grazing angles θ<30∘. It is shown that subcritical penetration is enhanced when the scale of volume fluctuations is comparable with the acoustic wavelength, and the scattered waves into the seafloor dominate over evanescent waves at depths larger than a few wavelengths.
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43.30.Ft Volume scattering

Three dimensional analyses of scattering by pressure-release sinusoidal surfaces

P. J. Welton

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 54-68 (2012); (15 pages)

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Scattering by pressure-release sinusoidal surfaces in three dimensions is analyzed using the Fresnel phase approximation and realistic source and receiver directivity approximations. Geometrical shadowing and second-order scattering are explicitly included to explore the validity of the Kirchhoff approximation. No restrictions on the surface heights and slopes are made. The “goodness” of the resulting expressions is verified by requiring the pressure scattered by a sinusoidal surface to reduce to the image solution as the surface amplitude goes to zero. The first-order scattered pressure achieves a very good approximation to the image solution, and the second-order scattered pressure goes to zero, as expected, under this requirement. The theory is compared with available experimental scattering measurements, and the agreement is good. Because the slopes on the experimental surface are very steep, shadowing corrections are indispensible to achieving accurate first and second order scattering results. Shadowing has a greater impact on the scattering prediction than the second-order scattering contribution. This suggests that the Kirchhoff approximation may be more robust when incorporated into a theory including a detailed shadowing treatment as well as the Fresnel phase approximation and a good directivity approximation.
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43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves

Three-dimensional analysis of scattering by pressure-release plane surfaces and the validity of the image solution

P. J. Welton

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 69-79 (2012); (11 pages)

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Because of the complexity of the scattering integrals in three dimensions, numerous approximations are used to obtain closed-form solutions. By considering the scattering by an infinite, pressure-release plane surface, the effects of various phase approximations and source directivity approximations can be examined independently of the surface roughness. Calculations are carried out using the Fraunhofer and Fresnel phase approximations, and two directivity approximations. It has been shown experimentally that the image solution is valid for the reflection of an acoustic beam by an infinite, pressure-release plane surface if the plane is in the farfield of the source. Consequently, the image solution is used to compare analytical solutions obtained using various phase and directivity approximations, and it is found that both the Fresnel phase approximation and a realistic directivity approximation are required to achieve a good fit. The solution produced by the Fraunhofer phase approximation is obtained as an asymptotic limit of the modified Fresnel solution. Criteria for the validity of the Fraunhofer and Fresnel phase approximations are developed. The Fresnel phase approximation is valid under fairly broad conditions, but the Fraunhofer phase approximation is never valid for an infinite plane surface that must be in the farfield of the source.
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43.30.Hw Rough interface scattering
43.20.Fn Scattering of acoustic waves

Sea-ice thickness measurement based on the dispersion of ice swell

David Marsan, Jérôme Weiss, Eric Larose, and Jean-Philippe Métaxian

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 80-91 (2012); (12 pages)

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The dispersion of flexural waves propagating in the Arctic sea ice cover is exploited in order to locally measure the ice thickness. The observed dispersion, for waves filtered in the 4–20 s period interval, at up to 4 broad-band seismometers deployed in Spring 2007 near the North Pole, is compared to a parameterized model that accounts for a complex wavefield made of a superposition of independent plane waves with different amplitudes and back-azimuth angles. The parameterization, that includes finding the best modeled ice thickness, is performed by using the cross-correlation functions between the seismometers. The ice thickness is estimated to 2.5±0.2 m for the ~1 km-large floe the seismic stations were deployed on, which is coherent with other, independent measurements at this site. This study thus demonstrates the feasibility of using broad-band seismometers deployed on the sea-ice in order to passively measure the ice thickness, without requiring active sources nor human intervention.
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43.30.Ma Acoustics of sediments; ice covers, viscoelastic media; seismic underwater acoustics
43.28.We Measurement methods and instrumentation for remote sensing and for inverse problems
43.40.Dx Vibrations of membranes and plates
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics

Underwater radiated noise from modern commercial ships

Megan F. McKenna, Donald Ross, Sean M. Wiggins, and John A. Hildebrand

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 92-103 (2012); (12 pages)

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Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (<1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1μPa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1μPa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.30.Xm Underwater measurement and calibration instrumentation and procedures
43.50.Cb Noise spectra, determination of sound power
43.50.Ba Noisiness: rating methods and criteria

Underwater ambient noise on the Chukchi Sea continental slope from 2006–2009

Ethan H Roth, John A. Hildebrand, Sean M. Wiggins, and Donald Ross

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 104-110 (2012); (7 pages)

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From September 2006 to June 2009, an autonomous acoustic recorder measured ambient noise north of Barrow, Alaska on the continental slope at 235 m depth, between the Chukchi and Beaufort Seas. Mean monthly spectrum levels, selected to exclude impulsive events, show that months with open-water had the highest noise levels (80–83 dB re: 1 μPa2/Hz at 20–50 Hz), months with ice coverage had lower spectral levels (70 dB at 50 Hz), and months with both ice cover and low wind speeds had the lowest noise levels (65 dB at 50 Hz). During ice covered periods in winter-spring there was significant transient energy between 10 and 100 Hz from ice fracture events. During ice covered periods in late spring there were significantly fewer transient events. Ambient noise increased with wind speed by ∼1 dB/m/s for relatively open-water (0%–25% ice cover) and by ∼0.5 dB/m/s for nearly complete ice cover (> 75%). In September and early October for all years, mean noise levels were elevated by 2–8 dB due to the presence of seismic surveys in the Chukchi and Beaufort Seas.
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43.30.Nb Noise in water; generation mechanisms and characteristics of the field
43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
43.60.Cg Statistical properties of signals and noise

Sensitivity kernel for surface scattering in a waveguide

Jit Sarkar, Christian Marandet, Philippe Roux, Shane Walker, Bruce D. Cornuelle, and W. A. Kuperman

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 111-118 (2012); (8 pages)

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Using the Born approximation, a linearized sensitivity kernel is derived to describe the relationship between a local change at the free surface and its effect on the acoustic propagation in the water column. The structure of the surface scattering kernel is investigated numerically and experimentally for the case of a waveguide at the ultrasonic scale. To better demonstrate the sensitivity of the multipath propagation to the introduction of a localized perturbation at the air-water interface, the kernel is formulated both in terms of point-to-point and beam-to-beam representations. Agreement between theory and experiment suggests applications to sensitivity analysis of the wavefield for sea surface perturbations.
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43.30.Pc Ocean parameter estimation by acoustical methods; remote sensing; imaging, inversion, acoustic tomography
43.30.Hw Rough interface scattering

Single-receiver geoacoustic inversion using modal reversal

J. Bonnel, C. Gervaise, B. Nicolas, and J. I. Mars

J. Acoust. Soc. Am. Volume 131, Issue 1, pp. 119-128 (2012); (10 pages)

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This paper introduces a single-receiver geoacoustic-inversion method based on dispersion analysis and adapted to low-frequency impulsive sources in shallow-water environments. In this context, most existing methods take advantage of the modal dispersion curves in the time-frequency domain. Inversion is usually performed by matching estimated dispersion curves with simulated replicas. The method proposed here is different. It considers the received modes in the frequency domain. The modes are transformed using an operator called modal reversal, which is parameterized using environmental parameters. When modal reversal is applied using parameters that match the real environment, dispersion is compensated for in all of the modes. In this case, the reversed modes are in phase and add up constructively, which is not the case when modal reversal is ill-parameterized. To use this phenomenon, a criterion that adds up the reversed modes has been defined. The geoacoustic inversion is finally performed by maximizing this criterion. The proposed method is benchmarked against simulated data, and it is applied to experimental data recorded during the Shallow Water 2006 experiment.
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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.Bp Normal mode propagation of sound in water
43.60.Hj Time-frequency signal processing, wavelets
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