bluuebunny/crossref_metadata_2025 huggingface dataset:
HLA/VLA broadband adaptive beamforming detection performance comparison in shallow water
Authors: Hodgkiss William S. , Murray James J. , D’Spain Gerald L. , Kim Katherine H. , Booth Newell O. , Schey Philip W. , Rice Joe
Published: October 2005

A broadband adaptive beamforming detection performance comparison is presented for a vertical array with matched-field replica vectors and a horizontal line array with plane-wave replica vectors. The data analyzed consists of both multitone (50–200 Hz) and full broadband (75–150 Hz) transmissions recorded during SWellEx-3 (shallow water evaluation cell experiment 3). SWellEx-3 was carried out in July 1994 west of Point Loma in approximately 200-m-deep water. A MPL vertical array was deployed from the R/P FLIP and the NRaD SWSS (shallow water sensor string) horizontal line array was co-deployed 500 m to the east. Source tows (multitone transmissions) and stations (full broadband transmissions) were carried out at various levels spanning a 22- and 16-dB dynamic range, respectively. Radar data will be included indicating the location and dynamics of interfering noise sources from shipping traffic in the area. [Work supported by ONR, Code 321US.]
Source localization in the Gulf of Mexico
Authors: Michalopoulou Zoi-Heleni , Porter Michael B. , Ianniello Jack
Published: October 2005

Data collected during the Gulf of Mexico experiment were processed for the estimation of the source location and the bottom depth of the water column at the site of the experiment. The data consist of time series received at five vertically separated hydrophones after the transmission of a pulse in the 100to was achieved with simulated annealing. Using the calculated parameter estimates in simulations, a remarkable match was observed between real and synthetic data.
Auditory backward recognition masking: Influence of musical meaning on pitch relationship between first and second sounds
Authors: Kakita Yuki , Hamada Takahasi
Published: October 2005

Auditory backward recognition masking (ABRM) refers to the interference of a second sound on recognition of another sound presented earlier in time. The influence of musical meaning on recognition of the first sound was investigated using the stimuli where the pitch relationship between the first and second sounds composed a triad. Four complex tones consisting of three tones differing in pitch were presented as stimuli. The frequency relationship of two complex tones composed a triad. The others did not compose a triad. One of the three tones of the complex tones was employed as a first sound. The others were employed as a second sound. The task was to label the stimuli as one of the four complex tones. The effect of the differences in the stimuli was evaluated using the percentage of correct responses as a function of ISI. Backward recognition masking was observed with the two sounds that did not compose a triad. The performance was better when the two sounds composed a triad rather than when they did not compose a triad. The results indicated that interference of a second sound on recognition of a first sound is reduced when there is musical meaning in the pitch relationship between the first and second tones.
Acoustic detection of inertial microcavitation from ultrasound
Authors: Roy Ronald A.
Published: October 2005

Recent years have witnessed a growing interest in processes governing the nucleation, perpetuation, and physical consequences of inertial microcavitation generated by ultrasound. Fields as diverse as medicine, ultrasonic cleaning, and sonochemistry all rely, in varying degrees, on our ability to either inhibit, promote, or control inertial cavitation activity. Quantitative, spatially resolved assessment of such activity often requires an ability to detect bubbles as small as a micron lasting less than a microsecond. This constitutes a technical challenge that has sought the services of optical, electrical, and acoustical technologies. A review is presented of the state of the art of spatially resolved, acoustic microcavitation detection schemes. This will include descriptions of both passive [Atchley etal., Ultrasonics 26 (1988)] and active [Roy etal., J. Acoust. Soc. Am. 87, 2451 (1990)] systems. Although these systems were designed to detect inertial microcavitation generated by microsecond pulses of Megahertz-frequency ultrasound (similar to that utilized in diagnostic ultrasound), the techniques are quite straightforward and generalizable to any situation where one seeks to detect spatially discrete cavitation activity in a reasonably homogeneous bounded liquid. Issues such as absolute sensitivity and observational invasiveness are discussed. [Work supported by NIH through Grant No. RO1 CA39374.]
Detection of cavitation during clinical extracorporeal lithotripsy
Authors: Coleman Andrew J. , Choi Min J. , Saunders John E.
Published: October 2005

A clinical cavitation detection system has been developed that monitors the amplitude-time variation of the 1-MHz component of the broadband acoustic emission expected to accompany bubble collapse during clinical extracorporeal shockwave lithotripsy [C. C. Church, J. Acoust. Soc. Am. 86, 215–227 (1989)]. The detector is based on a hand-held piezoceramic focal bowl hydrophone that is acoustically coupled to the patients’ skin. A commercial electromagnetic positioning device (Fastrak, Polhemus Inc., Vermont) is used to enable the reception zone of the hydrophone to be directed under ultrasound image guidance. The system has been tested in the clinic by monitoring acoustic emission from positions around the beam focus of a clinical shockwave lithotripter during routine lithotripsy. The detected acoustic emission shows features characteristic of those obtained from cavitation observed invitro and arises from within a region of similar dimensions to that of the hyper-echoic region that can be simultaneously observed in the B-scan image. The study provides evidence that acoustic emission from cavitation in tissue can be detected noninvasively during clinical lithotripsy.
Correlation of cavitation-induced damage to blood elements with passive acoustic detector output
Authors: Everbach E. Carr , Makin Inder Raj S. , Francis Charles W.
Published: October 2005

A 20-MHz probe transducer placed confocally with a 1-MHz cavitation transducer was used to detect inertial cavitation in human blood preparations [Huertas etal., J. Acoust. Soc. Am. 95, 2856(A) (1994)]. The preparations included suspensions of red blood cells (RBCs) and platelets in autologous plasma with or without the addition of Albunex (R) microbubble contrast agent. Damage to RBCs and platelets was measured hematologically and correlated with statistical descriptors of the fluctuating voltages from the passive cavitation detector. Good correlations were obtained between the average rms cavitation signal and percent hemolysis of diluted RBCs. In the platelet preparations, detector output paralleled damage as measured both by Coulter counter and by leakage of radiolabeled chromium-51 through platelet membranes. Advantages and shortcomings of the passive acoustic detection scheme used to predict cavitational damage to blood constituents will be discussed. [Work supported by an NSF PFF.]
Pulse width measurements of sonoluminescence in cavitation-bubble fields
Authors: Matula Thomas J. , Roy Ronald A. , Mourad Pierre D.
Published: October 2005

Recent studies involving sonoluminescence have focused on the properties and behavior of single bubbles in isolation. Some properties of single-bubble sonoluminescence (SBSL) appear to conflict with well-known properties of sonoluminescence from cavitation fields (MBSL). Direct comparisons between MBSL and SBSL have been difficult due to the difficulty in generating SBSL in nonaqueous solutions. A recent study comparing MBSL and SBSL [T. J. Matula etal., J. Acoust. Soc. Am. 96, 3252(A) (1994)] has shown that aqueous solutions of nonvolatile solutes show distinct differences in the corresponding spectra. The differences are attributed to differences in the relative symmetry of collapse of bubbles in cavitation fields versus in isolation. As part of the ongoing study to compare MBSL and SBSL, measurements were made of the apparent flash width of sonoluminescence from cavitation fields. Various well-defined cavitation regions were studied and compared to SBSL flash widths using an identical PMT for both cases. Both invasive and noninvasive mechanisms for generating MBSL were studied to determine the relative influence of ultrasonic horn immersion. Progress toward identifying the similarities and dissimilarities between MBSL and SBSL should lead to an improved understanding of sonochemical reactions. [Work supported by ONR.]
Influence of turbulent intermittency on acoustic scattering in the atmosphere
Authors: Wilson D. Keith
Published: October 2005

The classical treatment of wave scattering by turbulence does not account for the influence of turbulent intermittency. Intermittency causes quantities such as the scattering cross section to vary in space and time. It is particularly important to account for intermittency when there are energetic eddies having dimensions larger than the scattering volume, as is typically the case for scattering problems involving atmospheric turbulence. The conditional-probability method developed by Gurvich and Kukharets for incorporating intermittency effects will be discussed and applied to the problem of acoustic wave scattering by atmospheric turbulence. It will be shown that intermittency can dramatically increase the probability of measuring large values of the scattered intensity. The effect of combined intermittency in the temperature and velocity fields will also be considered.
Experimental observation of the effects of turbulence intermittency on scattered sound
Authors: Havelock David I.
Published: October 2005

Fully developed turbulence follows the well-known Kolmogorov spectrum and, within the inertial subrange, is governed by a single parameter ε called the viscous dissipation rate. Under stationary conditions the intensity of sound scattered from turbulence follows an exponential distribution with mean intensity I0 determined by ε. In a more realistic turbulence model, the viscous dissipation rate for a given scattering volume fluctuates with a log-normal distribution. The corresponding fluctuations in I0 cause the intensity distribution to deviate from the exponential distribution. In particular, the tail of the distribution is raised, providing more frequent occurrences of higher intensity levels. This effect impacts on target detection probability in acoustic remote sensing applications. It is shown that the deviations from an exponential distribution are clearly observable in direct measurements of sound intensities within a refractive shadow near the ground. The variance σ of the fluctuations in the dissipation rate is estimated by comparing the measured and theoretical distributions. It is also shown that σ cannot be obtained directly from short-term estimates of I0.
New formulations for the scattering of sound in a moving random medium
Authors: Noble John M. , Ostashev V. E.
Published: October 2005

The main aim of the presentation is the review of the modern theory of sound propagation and scattering in media with random inhomogeneities of the adiabatic sound speed, density, and medium velocity (mainly, in the atmosphere and ocean). This theory has been intensively developed in the last few years and includes the rigorous calculations of sound field statistical moments using Born approximation, ray, Rytov, and parabolic equation methods, and the theory of multiple scattering. This modern theory also shows that certain equations for statistical moments of the sound field propagating in the turbulent atmosphere, which previously have been widely used in the literature, must be revised. On the basis of the theory developed, new possible methods for acoustic remote sensing of the atmosphere are proposed.
Importance of the near-ground sound-speed profile in prediction of sound fields in a refractive shadow
Authors: Stinson Michael R.
Published: October 2005

The influence of the vertical sound-speed profile on sound propagation in an acoustic shadow has been investigated. For upwardly refracting conditions with both source and receiver near the ground, the profile in the first couple of meters nearest the ground can be critically important in determining the sound-pressure level in the acoustic shadow. A meteorological tower has been used to determine sound-speed profiles, in conjunction with acoustical propagation experiments. Wind speed and direction measured at a 10-m height and temperatures measured at heights of 8.7 and 2 m are used with similarity scaling expressions [L’Espérance etal., Appl. Acoust. 40, 325–346 (1993)] to obtain predicted vertical profiles for wind speed, temperature, and sound speed. These predicted profiles can be tested using additional measurements of wind speed and temperature at other heights. It is found that the similarity-based profiles do not always describe the actual profiles close to the ground. The implications for the prediction of sound fields in an acoustic shadow are investigated numerically using a fast, parabolic equation approach that includes profile, atmospheric turbulence, and ground impedance effects.
Efficient computation of sound field in horizontally stratified media using a WKB-type approximation with Airy functions
Authors: Li Y. L.
Published: October 2005

Conventional fast field programs model a general refractive index profile with a system of horizontal layers. The choice of layer thickness and number of layers depends on frequency, range, and intrinsic properties of the refractive index profile. These constraints result in excessive computation time for many practical cases. To avoid the long run times associated with the layered model, a WKB-type approximation with Airy functions has been applied to the efficient computation of the height-dependent acoustic pressure. Numerical results demonstrate that the new fast field program can reduce the computer time about 50-fold. For higher frequencies, the new fast field program can save more computer time. [Work supported by the US Army CERL.]
An improved approximation for sound propagation in a medium with a linear sound-speed profile
Authors: White Michael J. , Li Y. L. , Tai Jianfeng
Published: October 2005

The use of a refractive index profile whose square varies linearly with height is a common approximation when solving for the sound propagation in a refracting atmosphere. Its solutions are more tractable than those for an atmosphere whose sound speed varies linearly with height, although the linear sound-speed profile is more often the one whose solution is sought. In this paper, the approximate relationship between the two profiles has been examined. Numerical examples show that the two profiles give similar solutions for the sound pressure only when the background atmosphere is upward refracting. When the atmosphere is downward refracting, however, the two profiles give results that disagree except when the refraction is extremely small. In this paper, an improved approximate solution for the pressure field is given for the linear sound-speed profile. The solution is based on a WKB-type approximation which uses Airy functions as the general solutions of the wave equation. Numerical comparisons are made to show that the new approximation adequately models the sound field for the linear sound-speed profile for a wide range of detector heights and gradients and for both upward and downward refracting atmospheres.
Tank field data compared with fast field program
Authors: Klein Dean , Noble John M.
Published: October 2005

Acoustic data were recorded from various tanks traveling a known path at constant speed. The data were compared with the fast field program (FFP) to determine how well the FFP model would collate with actual data covering a range up to 2 km. This was done to determine if the FFP could be used to reliably predict the propagation effects of the environment for acoustical arrays listening for tanks. As the tanks were run through their course, meteorological data were also recorded. The meteorological data included temperature, relative humidity, barometric pressure, wind speed, and wind direction from the surface to 2000 m. The comparisons were encouraging through most cases until tank transmissions were buried in the background noise.
Information integration of frequency and duration
Authors: Irwin Robert D. , Weber Daniel L.
Published: October 2005

The distribution discrimination procedure can be used to evaluate a listener’s ability to discriminate along a single dimension of an auditory signal. This can be accomplished by sampling from two different distributions of the parameter and asking the listener to identify which sample was most likely to have come from the distribution with the higher mean. Information integration can be measured as the improvement in performance when multiple samples are presented. Whether information integration appears to be different for frequency discrimination and duration discrimination was examined. Subjects discriminated duration or frequency in a 2IFC task when different numbers of samples were presented. In the discrimination of the duration of a 1-kHz sinusoid, samples were drawn from normal distributions with either a mean of 100 or 130 ms; both had a variance of 900 ms. In the discrimination of the frequency of a 100-ms sinusoid, samples were drawn from normal distributions with means of 565 and 570 Hz and a variance of 25 Hz and from distributions with means of 565 and 585 Hz and a variance of 400 Hz. These conditions should be alike to an ideal observer in that all involve a standard deviation equal to the difference between their means. The majority of the listeners show better information integration for signal duration than signal frequency. [Work supported by AFOSR through WPAFB AL/CFBA.]
Acoustical instrument calibration: A regulatory agency viewpoint
Authors: Crivaro Michael A.
Published: October 2005

The Mine Safety and Health Administration (MSHA) has the responsibility of protecting the hearing of the nation’s miners. Within MSHA, the Office of Technical Support has determined a method of assuring that the noise dosimeters and acoustical calibrators used to conduct noise surveys provide an accurate representation of the miner’s noise exposure. The method is comprised of three components. First, the dosimeters and calibrators are evaluated based on recognized standards. Second, each calibrator and dosimeter is calibrated annually in a laboratory using instrumentation with accuracies traceable to the National Institute of Science and Technology. Finally, mine inspectors who conduct the noise surveys are trained on using their instruments correctly including performing a field calibration both before and after the noise exposure measurement.
Progress report and discussion on the continuing activity of ASA’s role in noise and its control
Authors: DuBois T. James
Published: October 2005

A discussion meeting sponsored by the Technical Committee on Noise is held to review progress made to date on the actions initiated at the Denver meeting in 1993 to increase the role of the ASA in noise and noise control. Members of the steering committee and others involved in related supporting activity will review specific progress made in the areas of education, increasing public awareness about noise and noise control, and encouraging joint activity in this area with other professional organizations.
Scattering of acoustic waves from rigid targets in stratified waveguides
Authors: Udagawa T. , Knobles D. P.
Published: October 2005

Two complementary methods are proposed for exact numerical calculations of the acoustic field scattered by a rigid sphere in an isovelocity fluid layer overlying a horizontally stratified medium. These two methods are based on the partial wave and Fourier expansions of the medium Green’s function. It is shown that the method based on the partial wave expansion is useful for clarifying the physical nature of the approximation involved in the method proposed by Ingenito some time ago [F. Ingenito, J. Acoust. Soc. Am. 82, 2051 (1987)]. It is in fact shown that the Ingenito approximation is equivalent to replace the exact medium Green’s function by that of the free-field Green’s function in obtaining boundary values of the field on the surface of the target. Numerical studies are performed and it is demonstrated that the exact results obtained by using the presently proposed methods are largely different from those obtained by using Ingenito’s approximation. In addition more complex cases are examined where the target is nonspherical and the waveguide is bottom limited as is commonly found in shallow water ocean waveguides. The sensitivity of the scattered field to various types of geoacoustic profiles when the target is near the sea floor is also considered.
Horizontal refraction of 3-D curvilinear wedge modes
Authors: Mignerey Peter C.
Published: October 2005

For shallow-water acoustic propagation, the wavelength is commensurate with the water depth but short compared to the horizontal extent of the problem. Under these conditions a sloping bottom causes the development of normal modes having wavefronts that are curved in the vertical direction. For simple slopes, such wedge modes have been shown to propagate with cylindrical wavefronts along characteristics in the horizontal plane. This work extends adiabatic wedge mode theory to regions of arbitrary bathymetry by constructing a three-dimensional curvilinear coordinate system that follows the contours of the ocean bottom. The requirement for separation of the depth coordinate from the coupled horizontal coordinates produces a nonlinear differential equation for a potential field. The gradient of this field then gives the depth scale factors and curved shape of the wedge modes. A standard normal mode problem is then solved to obtain the curvilinear wedge modes and a ray-trace method is used to study the horizontal motion of those modes. An overview of the model formulation and some examples will be presented.
Intensity moments of underwater sound reflected by a Gaussian spectrum corrugated surface: Measurements and comparison with a catastrophe theory approximation
Authors: Stroud John S. , Marston Philip L. , Williams Kevin L.
Published: October 2005

A surface, manufactured out of Styrofoam, provided a pressure release surface for an underwater, forward-scattering investigation. This surface was a single realization from a population of Gaussian spectrum random rough corrugated surfaces (rms roughness 1.5 cm, correlation length 10 cm). A broadband omnidirectional source was operated in the frequency range of 95–400 kHz and a broadband receiver was used to measure sound scattered from the surface. The frequency dependence of the mth higher-order intensity moments Im was measured and compared to theoretical predictions [M. V. Berry, J. Phys. A 10, 2061–2081 (1977)] that Im is proportional to kνm (for m≳2), where k is the wave number and νm is a twinkling exponent, and that I2∝ln k. Also, the dependence of I2 on distance from the surface was examined at a single frequency utilizing various pulse durations. It is known that far from a surface the wave field will obey Gaussian statistics (I2=2). For short pulses, however, the statistics of the wave field are strongly dependent upon individual reflections. For longer pulses this is the case as well near the surface, but as one moves away it is shown that the Gaussian limit is approached. [Work supported by ONR.]
Effects of scattering-induced frequency spread on Doppler performance
Authors: Eller Anthony I. , Daley Ellen M.
Published: October 2005

Frequency spreading caused by forward scatter from a dynamic rough surface will degrade the performance of active acoustic systems that are attempting to identify slowly moving targets against a reverberation background. This paper addresses the sequence of calculations and the approximations made to the governing physics in a system performance model whose primary output is a measure of target detectability at all locations in a two-dimensional grid. The relative frequency spreading resulting from system geometries and motion, active waveform shaping, and boundary interactions are compared and are related to Doppler detection performance as a function of environmental conditions. The received reverberation is characterized by the Q function, which is then convolved with an environmental spreading kernel based on the surface wave power spectral density. The scattering angles and frequency of boundary interaction are determined by shallow water propagation codes.
Nonlinear tomographic inversion by using the WKB modal condition
Authors: Shang E. C. , Wang Y. Y. , Voronovich A. G.
Published: October 2005

In the HRT (horizontal refraction tomography) scheme [A. G. Voronovich and E. C. Shang, J. Acoust. Soc. Am. 95, 2851(A) (1994)], the 3-D tomographic inversion is performed in two stages: (1) retrieving the modal wave numbers km(x,y) in the horizontal plane and (2) reconstructing the sound-speed profile SSP in the vertical at each node of the horizontal plane basing on a set of retrieved modal wave numbers km(x,y). Usually, a nonlinear approach has to be considered for the 1-D vertical inversion of the second stage. In this paper, the nonlinear inversion by using the WKB modal condition is proposed. The advantages of using WKB modal condition are: (a) it is efficient, the data km(x,y) can be matched directly to SSP without a model-based calculation (replica); (b) it works even if just a few modes are available; and (c) the error can be analyzed. Some results of numerical simulation are discussed. [Work supported by ONR.]
Calculating received time-domain amplitude and phase from 3-D ray tracing results
Authors: Grabb Mark , Birdsall Ted
Published: October 2005

For long-range sound propagation simulations, ray tracing has many advantages as well as drawbacks. Some of the advantages ray tracing offers are 3-D implementation with present-day computers and the capability of propagating only the acoustic field that will contribute to a single early arrival. Well-known drawbacks to ray tracing computations are the neglect of diffraction effects, infinite-amplitude results at caustics, and the often quoted ‘‘high-frequency approximation.’’ However, other simulation techniques have advantages and drawbacks as well, suggesting the community should use many of the available propagation techniques and build strong conclusions through assimilation of results. Here, a ray-endpoint density method is investigated for calculating the time-domain amplitude of a received early arrival. Also, computation of the received time-domain phase is studied. The methods are investigated using 2-D range-invariant, 2-D range variant, and 3-D time and space variant computational ocean sound-speed models. The ray-endpoint density method is compared against normal mode, PE, and dynamic ray tracing results. [Work supported by ONR-ASSERT.]
Nonlinear FM short-duration waveform design procedure for travel-time measuring systems
Authors: Grabb Mark , Birdsall Ted
Published: October 2005

Many oceanographic experiments and sonar systems require a short-duration, low-frequency, large bandwidth interrogation waveform for the purpose of obtaining precise travel-time measurements. The waveforms employed can typically be classified into three categories: short pulse, digital burst, or FM sweep (chirp). The FM sweep is the most flexible waveform class in that it can have arbitrary duration and amplitude while supplying desirable matched filter output properties (high resolution and low time-domain sidelobes). A design procedure has been developed to produce nonlinear FM burst waveforms that closely obtain a ‘‘desired’’ energy spectral density and hence matched filter output. A transmitter-to-receiver system analysis of the waveform has been conducted that includes a linear model of the transducer. The system analysis unveils the significant benefits of knowing the transducer characteristics precisely as well as uncovers the need for a transmitter clock rate that is significantly higher than the waveform’s Nyquist rate. [Work supported by ONR-ASSERT.]
Data analysis and inversion of basin scale sound propagation in the Western Mediterranean Sea
Authors: Fujimori Hidetoshi , Nakano Iwao , Tsukioka Satoshi , Lynch James F. , Newhall Arthur E.
Published: October 2005

In 1994, an ocean acoustic tomography experiment was performed in the Western Mediterranean Basin. It is a pilot tomography project for monitoring in this area. This project is called THETIS and constructed by European tomography groups. The S-Tether system was deployed in this experiment. This system consists of a 400-Hz tomography transceiver made by Webb Res. Co. and a surface buoy developed by WHOI and JAMSTEC. The received data from four other transceivers to the S-Tether were analyzed. The distances from S-Tether to four communicated transceivers were about 250–450 km. Sound was propagated four times a day from late January to late October in 1994. In the Mediterranean Sea, the sound velocity increases with depth from the surface down to the bottom and sound propagates in the surface sound channel. A simple inversion was used for this analysis. This method is effective for this surface sound channel. The time series of the temperature distribution was obtained. These are the vertical profiles averaged along the horizontal ranges. Seasonal changes are observed from the temperature time series. In the winter, a flat temperature distribution was covered from the surface to the bottom. It is considered to be sinking, which is a typical phenomena in the Mediterranean Sea.
Acoustic tomography in the Western Mediterranean from a moving ship
Authors: Mikhin Dmitry Yu. , Burenkov Sergey V. , Chepurin Yury A. , Goncharov Valerii V. , Kurtepov Vladimir M. , Selivanov Viktor G. , Godin Oleg A.
Published: October 2005

A moving ship tomography experiment was carried out in the Western Mediterranean in 1994. Broadband sound signals were emitted by six moored transceivers deployed by IfM (Kiel, Germany), IFREMER (Brest, France), and WHOI (Woods Hole, USA), in the framework of the THETIS–2 project and recorded at a hydrophone deployed from a drifting research vessel. The acoustic measurements were supplemented with a detailed CTD survey. The data processing technique used made it possible to compensate for the Doppler shift due to vessel drift, measure the channel pulse response and estimate the arrival angles of different rays. The arrival pattern proved to be consistent with numerical predictions using adiabatic normal modes and ray theory. The first results of tomographic inversion for a single vertical slice are presented. The travel times of early raylike arrivals and final cutoffs constitute the data set for inversion. For distances over 300 km, late modal arrivals were resolved, identified and incorporated into the data set. An alternative inversion approach based on matching the overall arrival pattern is discussed and compared with traditional schemes. [Work supported by ISF, INTAS, and RBRF.] a)On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.
Simulations of acoustic tomography of ocean currents in a coastal region
Authors: Godin Oleg A. , Mikhin Dmitry Yu.
Published: October 2005

A new, full field approach to acoustic monitoring of currents in the ocean—matched nonreciprocity tomography (MNT)—was recently put forward [Godin etal., in FullFieldInversionMethodsinOceanandSeismo-Acoustics, edited by O. Diachok etal. (Kluwer, Dordrecht, 1995), pp. 261–266]. The approach is based on inverting nonreciprocity in phase of a cw signal measured at a set of points in a given vertical plane. MNT was designed to overcome the problems with rays resolution and identification which make the traditional current tomography technique inapplicable in coastal regions. Results of numerical simulations of suggested MNT field experiments in the Strait of Florida will be presented. The possibility to increase resolution and robustness of the inversion with few transceivers by using wideband signals is considered. The amount of apriori environmental information required for an unambiguous currents inversion by MNT is evaluated. The possibility of simultaneous measurements of both horizontal components of current velocity is also addressed. Finally, the effects of surface and internal waves on the acoustic monitoring of ocean currents are analyzed. [Work supported by NRC and RBRF.] a)On leave from P. P. Shirshov Oceanography Institute, Moscow, Russia.
Paleo-ocean acoustics: The historical variation of low-frequency sound absorption in the world’s oceans and the implications for sea mammals
Authors: Browning David G. , Mellen Robert H.
Published: October 2005

Sound is the primary method of communication in the ocean. The absorption of sound in seawater limits the range and fidelity of communication. This absorption is due to three chemical relaxation mechanisms which, of course, would vary with any change in their constituents, such as sulphur, magnesium, or carbon; or any environmental parameters such as temperature. At the low frequencies (below 1 kHz) required for long-range communication, the principal absorption mechanism is also a pH-dependent buffered boric acid reaction. In turn, the pH in the ocean is controlled by the amount of dissolved carbon dioxide. All these factors could vary during the Earth’s evolution. Estimates are made of the possible changes in absorption and, hence, ocean communication conditions over the ages, based on the evolution of ocean as put forth by Holland [H. D. Holland. B. Lazar, and M. McCaffrey, Nature 320, 27–33 (6 March 1986)] and others, with emphasis on the time scale, approximately 50 million years, of ocean mammal development.
Investigation of sound absorption in the deep sea using a submergence vehicle
Authors: Tsuchiya Toshio , Amitani Yasutaka , Ochi Hiroshi , Shimura Takuya , Kikuchi Toshiaki , Umezawa Masaaki
Published: October 2005

For the design of underwater acoustic equipment, it is very important to estimate the sound absorption, especially since the longer the propagation range, the greater the effect of sound absorption. Generally, the equations of Thorp, Schlkin, and Marsh and Francois and Garrison are often used for the determination of sound absorption, but these equations yield values that are different from each other. So, the signal level from the data transmitter (center frequency: 20 kHz) of the deep submergence vehicle ‘‘Shinkai 6500’’ were measured in detail on the mother ship. The dives for this investigation were carried out at a maximum depth of 6500 m in the northwest Pacific area. It is found that Francois and Garrison’s equation was comparatively suitable for the measured data.
Remote ocean sensing by parametric array
Authors: Naugolnykh Konstantin A. , Esipov Igor B.
Published: October 2005

Parametric arrays launched by P. J. Westervelt as a result of an investigation of nonscattering of sound by sound [P. J. Westervelt, J. Acoust. Soc. Am. 35, 535–537 (1963)], have become familiar in the practice of marine research. The narrow beam of a wide frequency band parametric signal in the low-frequency range makes an attractive parametric array application for ocean sensing on a long-range acoustic pathway. Results of an experimental application of a high power narrow beam parametric array in a variety of environmental ocean conditions, that is, shallow water, long-range (up to 1000 km) signal propagation, and synoptic ocean eddy remote sounding, are considered in this paper. This space pattern of the parametric antenna field is shown to be essentially changed with the direction of the ocean eddy probing. Horizontal refraction occurs when a parametric signal passes through the eddy. This shows the possibility of a long distance tomographic analysis of mesoscale environment patterns of the ocean by a high-directed parametric array. The problem of parametric array application on elongated pathways in the ocean is discussed, the advantage of the parametric array with respect of a conventional one in the ocean waveguide is considered also. [Work supported by ISF grant MH 1300 and RFFI grant 95-02-06353a.]
A broad frequency anechoic lining system
Authors: Emery N. Scott , Ledoux Claude , Buchanan Eric
Published: October 2005

Testing in indoor underwater acoustic test tanks can be limited by ambient noise and by reflections from the tank’s surfaces. The severity of reflection problems is related to a tank’s dimensions and the acoustic reflectivity of the tank’s sufaces. To reduce reflection problems, a tank may be enlarged, but in most cases, this solution is not acceptable. An alternative solution is to modify the reflectivity of the tank’s surfaces by adding an anechoic lining to the tank. A broad frequency (1 to 100 kHz) anechoic lining system was designed and developed for the 700 000 gallon Acoustic Test Facility at the Naval Undersea Warfare Center in Newport, RI. To accomplish broad frequency absorption, two parallel gradual transition absorbers are used: low-frequency, triangular wedges arranged in rows 6 in. apart and high-frequency molded pyramids spaced approximately 1 in. apart. Both the wedges and pyramids are fabricated from specially formulated, microvoided-polyurethane composites. The system is designed to provide 8 to 33 dB of echo reduction between 1 and 100 kHz. Measured prototype performance exceeded 10 dB at frequencies above 1.8 kHz. System acoustic design and materials development are discussed. The results of acoustic testing are presented and compared to design predictions.
Development of a scanning laser Doppler vibrometer for imaging the surface velocity of a submerged vibrating object of arbitrary geometry
Authors: Caspall Jayme J. , Gray Michael D. , Caille Gary W. , Jarzynski Jacek , Rogers Peter H. , McCall George S.
Published: October 2005

An underwater scanning laser Doppler vibrometer (USLDV) was developed as part of a system for imaging the vibrations of submerged surfaces of arbitrary geometry. USLDV allows for measurement of in-plane and out-of-plane velocity components with scan resolution limited typically by the resolution of the positioning system (< 1 mm). The Georgia Tech system features a compact underwater probe mounted on an acoustically transparent mounting truss whose position and orientation is computer controlled. The system was designed with special consideration of the measurement of compliant surfaces underwater. Characteristically low impedance and locally reacting, compliant surfaces are sensitive to field perturbations, such as those which may be generated by the measurement apparatus. Small scattered fields can generate sizable local surface motion, leading to measurement error. The design of the underwater system components was performed in consideration of the perturbation sensitivity of compliant surfaces as well as such issues as sound-induced modulation of the index of refraction, and vibration of the probe head due to incident sound and/or the motion of the positioning truss. [Work supported by ONR.]
Acoustic material characterization by laser interferometry
Authors: Willis R. Lance , Stone T. Shane , Berthelot Yves H.
Published: October 2005

An interferometric system consisting of five independent probes cabable of measuring in-plane or out-of-plane surface motion of a vibrating sample at five different points simultaneously has been designed, constructed, and tested. A description of the design, measurement capabilities, and performance specifications will be given. The system utilizes optical fibers and compact probe design (30mm×15mm×9mm) to enable close spacing measurement points. Signal demodulation is performed by phase-locked loops allowing real-time measurements. The system is designed to test voided polymer samples excited by a shaker in the 100 Hz to 5 kHz range. It is calibrated for steady state and transient excitation of the sample. Results include measurements of the damping constant of the sample in the time domain for various frequencies of excitation. [Work supported by the Office of Naval Research, Code 334.]
An inverse acoustic problem in the presence of a mean flow
Authors: Patrick Sheryl M. , Atassi Hafiz M.
Published: October 2005

Recent research has shown the feasibility of performing inverse aeroacoustic problems for streamlined bodies. The unsteady pressure on a flat-plate airfoil, due to a convected vortical disturbance in the mean flow, can be recovered from the far-field radiated sound. The present paper extends this analysis to oscillating airfoils in a uniform mean flow. In this case, the oscillating airfoil creates an unsteady pressure field on the airfoil surface. The inverse problem, then, is to determine the surface pressure from the radiated sound. For the oscillating airfoil problem, the normal pressure gradient does not vanish along the airfoil surface, rendering the inversion process more complex than for the gust problem, however it is still feasible. This paper also compares the oscillating airfoil application to acoustic holography. While the two problems are similar mathematically, far-field input data are, in general, not sufficient for acoustic holography applications while they are sufficient for the inverse aeroacoustic problem.
Multilayered model for near-field acoustical holography of sound sources with hot surfaces
Authors: Gutiérrez V. Martín
Published: October 2005

Since near-field acoustic holography (NAH) is a powerful tool to investigate the sound radiation of a wide range of sources immersed in a homogeneous medium, a corrective model for the presence of inhomogeneities in the near field, where the hologram is performed, is presented. Strong temperature gradients modify the propagation of the sound wave, because they modify the density of the medium and then the sound speed. Many models were developed to take into account this and other effects; most of them were proposed in the atmospheric sound propagation area. The actual model was developed to minimized the effect of temperature gradients in the near field. An early model, previously presented [M. Gutiérrez and J. Arenas, J. Acoust. Soc. Am. 96, 3263(A) (1994)], based on the spatial transformation of sound fields technique, was modified in order to obtain a new mathematical expression based on a multilayered Green’s function. Some theoretical sources were numerically tested with the new model, which supposed a disturbance during heat transmission to the free air by an ‘‘omnidirectional’’ heat source. The comparative results between NAH theory and the proposed model will be shown.
Mode filtering of broadband signals for range-dependent shallow-water environments
Authors: Jaya Indra , Badiey Mohsen
Published: October 2005

A mode filtering technique is described and applied to broadband signatures obtained from recent shallow-water acoustic experiments [Badiey etal., J. Acoust. Soc. Am. 96, 3593–3604 (1994)]. The technique uses a combination of a wavelet transform and singular value decomposition. The order of the modes is arranged by means of their respective energy levels. Each energy level is directly associated with the eigenvalues of the decomposed signal. The progressions of modal structures in time and frequency are given for various azimuthal propagation paths. Evolution of modal structure with frequency is examined by measuring the extent of the frequency band for each propagation path. It is shown that the pattern of the modal structure becomes more complicated for higher modes. Furthermore, from the time-frequency analysis, it can be seen that the existence of a given mode can vary with time and that the medium filters the broadband signal. The mode shape is shown as a function of time, frequency, azimuth, sound speed in the sediment, and other shallow-water waveguide parameters.
Reduction of structure-borne noise using an air-voided elastomer
Authors: Ko Sung H.
Published: October 2005

A theoretical model was developed to evaluate the reduction of structure-borne noise which is generated by a line force applied on an infinite plate using an elastomeric baffle. The vibrating plate is covered with an elastomeric baffle layer to reduce the noise generated by the structural vibration. The vibrating plate is perfectly bonded to the elastomeric baffle. The outer surfaces of the vibrating plate and the elastomer baffle are in contact with air and water, respectively. The analysis for modeling is based on the theory of elasticity and pertinent boundary conditions. Effects of various parameters such as baffle layer dimensions and material properties on the noise reduction are presented.
Helmholtz resonator in the induction system of a spark-ignition engine with production versus prototype manifolds
Authors: Selamet A. , Yonak S. H. , Novak J. M.
Published: October 2005

Following an earlier work [A. Selamet and J. M. Novak, J. Acoust. Soc. Am. 97, 3393 (1995)], the present study investigates the performance of a Helmholtz resonator installed in the induction system of a Ford 3.0 ℓ V6 Vulcan engine in a dynamometer test facility. Earlier findings with the production manifold are compared with the current results obtained with a modified prototype manifold in an attempt to determine the extent of multidimensional wave dynamics. The induction system is instrumented with fast-response piezoresistive transducers to capture the temporal and the spatial variation of air pressure. Measured insertion loss characteristics of the silencer are then discussed in comparison with the predictions from a nonlinear computational fluid dynamics approach in the time domain.
Assessment of a fractal model for corona discharges in salt water
Authors: Jones H. M. , Epsinosa J. C. , Galloway M. L. , Gleeson A. M. , Rogers R. L.
Published: October 2005

The prebreakdown corona phase of a spark discharge in salt water produces a measurable acoustic pulse. This pulse is produced by the formation and collapse of a vapor bubble. The plasma has a multiply fingered shape, and it creates a bubble with a corresponding acoustic pulse. The rate of formation of plasma fingers may be a fractal dimension of the size of the discharge. A fractal model of the growth of the corona discharge can be used to connect the variables of voltage, current, and bubble wall acceleration. The dependence of the acoustic and electrical response and thus the fractal dimension of the corona growth on liquid conductivity, and applied voltage are investigated. The acoustic data are used to infer the bubble wall acceleration while the current-voltage data are measured directly and used to determine the total resistance of the plasma. The corona is formed by the application of high-amplitude electric fields to a set of electrodes that are immersed in the liquid. [Work supported by the Office of Naval Research under Grant No. N00014-94-1-0150.]