bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental observation of bending wave localization
Authors: Cody George , Ye Ling , Zhou Minyao , Sheng Ping , Norris Andrew N.
Published: October 2005

Localization of bending waves has been observed for the first time for two-dimensional (2D) acoustic wave propagation in an inhomogeneous composite system consisting of a steel plate decorated with two sets of randomly attached Lucite blocks. A significant experimental feature of the localized modes is an exponentially decay of the mode intensity from their peaked centers, with a decay length that increases as (f0−f)−1 when the mode frequency f approaches a quasimobility edge f0. The minimum attenuation length is of the order of a block diagonal and is about 40% of the banding wave’s wavelength. The experimental data, as well as results of finite-element calculations, identify the source of the localization phenomenon as strong scattering of the bending wave by shear and flexural resonances of the Lucite blocks. This result supports theoretical predictions that resonant scattering enhances localization [cf. ScatteringandLocalizationofClassicalWavesinRandomMedia, edited by P. Sheng (World Scientific, Singapore, 1990)]. Recent experiments on acoustic wave propagation in rough composite steel/refractory walls also exhibit exponential localization at frequencies corresponding to 3-D propagation. The experimental data suggest that a composite plate is a unique vehicle for the study of classical localization: at low frequencies, in 2-D and, at higher frequencies, in 3-D. The generic nature of the localization phenomenon suggests its application as a tunable attenuation mechanism for bending waves
Fluid loading of irregular structures
Authors: Crighton David G.
Published: October 2005

An analytically and computationally tractable model for the response of complex fluid-loaded structures is that of a plane elastic plate or membrane subject to static fluid loading and single-frequency localized mechanical drive, and reinforced by a number of parallel ‘‘ribs’’ in regular, partially ordered, or random configurations. Coupling along the structure is provided by subsonic surface waves (equivalent to nearest-neighbor mechanical coupling) and by long-range acoustic/hydrodynamic fields. A variety of analytical and computational studies carried out by the Cambridge group will be presented, showing large effects of an isolated irregularity, Anderson localization in extensively irregular configurations under surface wave coupling, and delocalization (short circuiting) by weak long-range fields. [Work supported by ONR, Code 1132SM.]
Shallow-water broadband source localization in range and bearing by matched fields
Authors: Knobles David P. , Mitchell Stephen K.
Published: October 2005

Data from a moving source received by three horizontally separated bottomed sensors in a shallow-water environment are analyzed using a broadband matched-field approach to source localization. The water depth was approximately 120 m, and the low bottom loss in the area results in low spatial coherence of the broadband field. The modeled acoustic fields are constructed via a ray model with wave-like corrections. Localizations are made in the x-y plane. The time evolution of the matched-field surfaces produced from the data agree well with simulated surfaces. Matched-field surfaces are generated successively in intervals of about 1.6 s in small search areas with a fine spatial grid to test the possibility of tracking a source. Results of the source tracking will be presented. The analysis also considers the effects of the sea floor and environmental mismatch of sea floor descriptions on localization in the context of spatial coherence. In addition the effect of varying the receiver separation on the ability to make a localization when a source is in the ‘‘broadside’’ region of the array is discussed. [This work is supported by the Office of Naval Research, Code 23, through Block RL3B.]
Vertical coherence of long-range reverberation in a Pekeris shallow-water waveguide
Authors: Zhou Ji-Xun , Zhang Xue-Zhen , Luo Ensheng , Wang Dezhao
Published: October 2005

By using the averaged angular spectrum method for a shallow-water sound field [Zhou, Acta Acust. Sin. 5, 86–99 (1980)], an expression of vertical coherence of long-range reverberation in a Pekeris shallow-water waveguide is derived. The resulting vertical coherence coefficient depends on bottom reflection and bottom scattering at small grazing angles. In this talk, sea-going experiments and laboratory data analyses are presented. The measured vertical cross-correlation coefficient for long-range reverberation is given as a function of relevant parameters such as reverberation time, hydrophone separation, signal frequency, etc. It is found that the measurements agree with theoretical predictions very well. The results are encouraging for further research on the derivation of both small-angle bottom reflection and scattering from long-range reverberation in shallow water. [Work supported by ONR and the IAAS.]
Adaptive multiuser receiver for shallow-water acoustic telemetry channels
Authors: Zvonar Zoran , Brady David , Catipovic Josko A.
Published: October 2005

Recent advances in coherent underwater communications technology are the backbone of an Acoustic Local Area Network (ALAN), which is designed for a real-time underwater telemetry with multiple sensors or unmanned underwater vehicles. In shallow-water areas ALAN is planned to cover 100–1000 km2 with nodes designed to communicate at 10 kbit/s at ranges of 3–4 nm. The communication protocol is optimized for a shallow-water acoustic environment, minimizing retransmission from finite-energy transceivers and taking into account time-variant link reliability and long propagation time between the nodes. One of the key elements of this protocol is a multiuser receiver capable of simultaneously demodulating signals coming from several asynchronous cochannel modems. Unlike spread-spectrum systems the narrow-band transmission is used. The propagation conditions in shallow water are severe due to the highly dynamic multipath structures and the adaptive multiuser receiver performs joint multiple-access cancellation, equalization, phase tracking, and bit timing recovery. It consists of fractionally spaced feedforward section, coupled digital phase-locked loops, and feedback sections, which utilize previous decisions both from the desired and the interfering user. The adaptive algorithm is the combination of the recursive least-squares algorithm for filter tap weights and a second-order phase update for the carrier recovery loop. Extensive testing has been carried out to confirm successful operation of the proposed receiver in a variety of propagation conditions using the experimental data provided by the Woods Hole Oceanographic Institution. The results indicate significant performance gain over the conventional receiver at the expense of a modest increase in complexity.
Simulated annealing and genetic algorithm in shear modulus inversion of shallow-water sediments
Authors: Turgut Altan
Published: October 2005

The shear modulus of the seabed is one of the most important geoacoustic parameters for modeling acoustic wave propagation in shallow water. A previously developed inversion method [Yamamoto and Torii, Geophys. J. R. Astron. Soc. 85, 413–431 (1986)] enables seabed shear modulus profiles to be determined by inverting measurements of gravity-wave induced sea-bed motion. It is a linearized inversion method that uses local derivative information to improve a starting model in an iterative fashion. Linearized inversions usually depend strongly on the starting model avoiding extensive exploration of model space and tend to be trapped around local minima. In this paper, two new global optimization methods, namely; simulated annealing and genetic algorithm, are introduced to avoid the limitations of the linearized inversion. Performance of these two methods has been tested by using both synthetic and real data and found to be highly efficient for the inversion of shear modulus profile of the seabed.
A new technique for measuring structural dynamic response
Authors: Wu Mei Q.
Published: October 2005

A modified cepstrum technique is introduced. It combines the cepstrum technique with an iteration procedure. The advantage of this technique is that it can determine the dynamic response of a structure from its vibration without any pre-knowledge of the excitation force. The restrictions of the technique are that it only applies to cases where the structural response is band limited in the frequency domain and the excitation force is short in time (comparing to the structural impulse response). When the structural response is not band limited, it can be determined in several limited frequency bands first and combined together later. In this paper, the theory of the modified cepstrum technique is reviewed, computer-simulated experiments are demonstrated, and an application example is presented. In the example, the magnitude of the structural dynamic response under 1400 Hz of a typewriter was determined by the modified cepstrum technique and compared to the dynamic response measured by conventional impulse excitation technique. The responses determined by the two techniques agreed well. [Work supported by IBM.]
Complex process controlling using wavelets
Authors: Ünal A. , Ercal F.
Published: October 2005

Complex process controlling requires a crucial reduction in the number of robust discriminitating features. The use of wavelet transformations with other artificial neural network-based methods will be given using real data.
Modeling of the vibration of a slotted beam under various conditions
Authors: Man XiuTing C. , Finch Robert D.
Published: October 2005

An analytical solution for the vibration of a slotted beam with clamped–clamped end conditions was presented previously [J. Acoust. Soc. Am. 92, 2311(A) (1992)]. The analytical solution for other classic end conditions, for example, free–free and pinned–pinned end conditions, is now presented. The theory is expanded to include damping as well. Solutions for general end conditions will also be presented. The effect of rotatory inertia, as in Timoshenko beam theory, is discussed quantitatively. Numerical results will be presented with some experimental results. [Work supported by NSF Grant No. MSS-9024224.]
Relationships among various room acoustic indices
Authors: Tachibana Hideki , Yamasaki Yoshio
Published: October 2005

For the last 5 years, the authors have been making acoustical surveys of auditoria in the world at every opportunity. In these acoustical measurements, room impulse responses have been measured using a dodecahedral omnidirectional loudspeaker, monaural microphones, and a dummy head system (Neumann KU81i). In order to get accurate impulse responses with high S/N ratio, the sweep-pulse method and synchronous averaging technique were adopted. From the monaural and binaural impulse responses measured in a lot of concert halls and theaters, such acoustic indices as T60 (reverberation time), EDT (early decay time), D50 (definition), C80 (clarity), Ts (center time), and IACC (inter-aural cross correlation) were obtained, and the relationships among them were statistically investigated. As a result, it has been found that such indices as D50, C80, and Ts are highly correlated with each other and the correlations between IACC and other monaural indices are very low. The binaural impulse responses measured through the dummy head were convolved with dry music and speech signals by digital technique, and they are being used as the test signals for subjective experiments using a transaural reproduction system.
Analysis of sound field on spatial information using a four-channel microphone system based on a regular tetrahedron peak point method
Authors: Sekiguchi Katuaki , Kimura Sho , Hanyuu Toshiki
Published: October 2005

This paper describes the development of a sound field measurement method that is aimed at analyzing spatial information of the sound field in a room. This measurement system has four microphones and each of them is installed at the apex of a regular tetrahedron. With this method spatial information of an individual wave front is analyzed from the impulse response at four points that are completely synchronized. With the introduction of a deconvolution method, measuring accuracy for waveform analysis is greatly improved and the analysis becomes much faster. By using models for which the image source positions are already known, experimental studies have been conducted on the identification of sound source positions and frequency distortion by repeated reflections. Furthermore, virtual sound sources have been detected and the waveform in actual sound fields have been recomposed. The results of these experiments indicate that the measurements are accurate and the measurement method can be used effectively.
A new physical measure for psychological evaluation of a sound field: Front/back energy ratio as a measure for envelopment
Authors: Morimoto M. , Iida K.
Published: October 2005

Broadening is one of the important characteristics for the psychological evaluation of a sound field. Several investigations indicated that broadening was comprised of two elemental senses, i.e., auditory source width (spaciousness) and envelopment [M. Morimoto etal., Proc. 13th ICA, Belgrade 2, 215–218 (1989); J. Acoust Soc. Jpn. 46, 449–457 (1990); and Hidaka etal., J. Acoust. Soc. Am. 92, 2469 (A) (1992)]. They inferred that the degree of interaural cross correlation of late reflections correlated with envelopment. This paper, however, shows the results of psychological experiments that envelopment is affected by the energy ratio of reflections coming from the front of the listener to those coming from the back of the listener, even if the degree of interaural cross correlation of the late reflections are equal. Namely, envelopment grows as the energy of the reflection coming from the back of the listener increases. This result suggests the need to measure the ratio which has never been measured.
The comparative evaluation of auditoriums—Theaters and concert halls
Authors: Veneklasen Paul S.
Published: October 2005

A valiant enterprise is underway to make difficult physical measurements in concert halls and to permit comparisons of these measures among the halls. Early experience is proving most valuable. In this paper full scale measurements will be related to similar information that can be derived in more specific detail from measurements in small models. The data also hold promise of correlation with presentations in auditorium synthesis, which has over the last 25 years furnished design criteria for model studies leading to completed auditoriums. However, the missing link in an invaluable chain of design correlation is the ability to make reliable subjective comparisons and preferential judgments of sound in auditoriums. Suggestions are given for limitations and requirements for the ability to conduct these measurements.
Spatial information measurements for investigating specular and diffuse sound fields in enclosures
Authors: Abdou A. , Guy R. W.
Published: October 2005

Attempts to predict the sound quality in large rooms can be made at the design stage using scale or computer simulation models but they are usually based on the assumption that the sound field is diffuse. Quality is said to be measured in existing rooms by known room-acoustic indicators but most of them have been developed without regard to direction sensing. Measurements in existing halls show that the sound field is far from diffuse. Specular and diffuse surface reflections not only vary from one room to another but also from seat to seat in the same room. To quantify this phenomena, both spatial and temporal diffuseness has to be investigated. Measuring the directional characteristics of sound in existing halls provides the prospect of quantifying such distribution. This work describes the development of a PC-based system to measure the spatial information of sound fields in large rooms. The system utilizes sound intensity measurement from three microphone pairs arranged in Cartesian coordinates or one pair in three successive orientations to calculate intensity vectors. The sound field can then be visualized on an energy directional basis versus arrival time and hence analyzed in greater detail than hitherto possible. The potential for quantifying spatial specular and diffuse sound fields will be discussed and example results presented. Such results may lead to new acoustic indices with respect to direction dictated quality. [Work supported by NSERC, Canada, Individual Operating Grant OGPIN 013.]
Comparisons of IACC and LF measurements in halls
Authors: Bradley John S.
Published: October 2005

Lateral energy fractions, LF, and inter-aural cross correlations, IACC, have both been proposed as correlates of spaciousness in concert halls. Although, theoretically, related previous measurements have not shown a strong relationship between the two quantities. New measurement results from 80 locations in 10 different halls indicate varying relationships in each of the 6 octave bands from 125 to 4000 Hz. At medium and higher frequencies both LF and IACC values vary among halls. At low frequencies only LF values vary significantly among halls. The two quantities are also shown to vary differently with position in halls. Statistical analyses of the data reveal other objective measures related to these two quantities.
Spectral formalism of wave propagation in a range-dependent shallow-water waveguide
Authors: Tang Dajun , Guo Yue-Ping
Published: October 2005

The study of acoustic wave propagation in a shallow-water environment invariably encounters the problem of range dependency, which usually comes in the forms of rough interfaces and medium inhomogeneity. For a range-independent, i.e., horizontally stratified problem where the wave equation can be solved using separation of variables, the well-established wave-number spectrum formulation has proved to be a powerful technique. When such a spectrum is known, the modal structure and its continuous component will completely determine the wave behavior in the waveguide. More importantly, knowledge of the spectral information can be used in inversion techniques to estimate environment parameters through acoustic probing. Here an approximate spectral formalism is developed for weakly range-dependent problems. More specifically, this approach is suitable for those cases where the change of environment is much slower than a horizontal wavelength. The formulation is based on an asymptotic expansion in which the lowest-order solution will result in the well-known adiabatic solution when the proper poles of the spectrum are evaluated. Since the field is expressed in the form of an approximate wave-number integral, a mode near its transition region where it changes from propagating to nonpropagating in the water column can be handled properly. In addition, higher-order solutions can be expressed in a simple recursive manner. Some examples will be discussed to elucidate this approach.
Comparison of two numerical models for acoustic transmission loss in shallow-water waveguides
Authors: Kargl Steven G. , Lim Raymond
Published: October 2005

Transmission losses for the propagation of an acoustic wave field due to a point source in shallow water to some point along the water–sediment interface are obtained from a fast-field algorithm (SAFARI) and an exact Green’s function benchmark [R. Lim, J. Acoust. Soc. Am. 92, 1593–1611 (1992)]. The shallow water environment is modeled as a horizontally stratified medium where the layer of water is bounded above by a semi-infinite layer of air and below by a sediment consisting of a thin transition layer and a semi-infinite subbottom. The sediment layers can be viscous fluids and viscoelastic solids as well as poroelastic materials in the Green’s function benchmark. The calculated transmission losses, that are to be discussed, correspond to a water depth of 12 m and a horizontal range that extends to 1 km. A critical comparison of SAFARI against the exact benchmark suggests that extra care be exercised in the application of fast-field algorithms to shallow water problems, even at long ranges.
On the measurement of environmental parameters with a volumetric array of hydrophones using the ambient acoustic field in an anisotropic, range-independent, shallow-water environment
Authors: Smith George B. , Byrne Charles L. , Chandler Howard A.
Published: October 2005

In a previous paper, a high-resolution estimator function that matched ambient acoustic field data from a vertical array of hydrophones to trial environments from a normal mode environmental model was used to estimate the parameters of the environment through which the acoustic energy passed. Shallow-water simulations were used to explore the response of the estimator as a function of several environmental parameters. The general conclusion was that the estimator produced unique and correct estimates for these parameters, but that the method probably would not extend, without modification, to volumetric arrays and anisotropic environments. In this work, it is shown that the inclusion of horizontal aperture (tilted line array) destroys the ability of this technique to distinguish the correct environment even when that environment is isotropic. Methods are explored to generalize the technique so that it works in anisotropic environments with volumetric arrays. [This work was supported by the Office of Naval Research, Program Element 61153N, with technical management provided by the Naval Research Laboratory, Stennis Space Center, MS.]
An experimental investigation of the AE source location and magnitude on 2-D frame structures using intelligent signal processing
Authors: Šribar Rok , Sachse Wolfgang
Published: October 2005

The results of experimental investigation of acoustic emission (AE) source characterization in 2-D frames is reported in this paper. Determination of the AE source location and magnitude from the displacement field is an inverse problem. It is known that humans have remarkable sensory abilities to undo a large number of demanding inverse problems with little effort. Here, nature is modeled by implementing intelligent signal processing algorithms to solve the problems of the AE source location and magnitude determination. The signal processing algorithms implemented are; FFNN trained by a modified back-propagation algorithm, and a linear system called an auto-associative processor (AAP). The standard feature of these algorithms is the use of a set of pre-processed, measured signals to form a system memory. The pre-processed signals used by the AAP algorithm are tutor augmented, while in the case of the FFNN the pre-processed signals are nonlinearly mapped to the training vectors provided by the tutor. The system memory is consequently utilized to process experimental signals to determine some of the AE source properties. [Work partially supported by NSF and ONR.]
Wavelet analysis of blade–vortex interaction noise
Authors: Constantine Wm. , Pezeshki C. , Mosher M.
Published: October 2005

Fourier analysis techniques for analyzing helicopter noise signals have been shown to be an adequate, yet inefficient tool for the design of helicopter noise control systems. Impulsive sources of noise, such as blade–vortex interaction (BVI) noise cannot be localized in time without collecting relatively large amounts of data at high sampling rates. Attempts to minimize the BVI phenomenon through helicopter blade control schemes in the Fourier domain are inherently inefficient since the control matrices must account for the large number of Fourier components needed to represent the signal. Time-frequency representations, such as the wavelet representation, offer an efficient alternative to these Fourier domain methods. Wavelet analysis has been performed on an ensemble of helicopter noise signals. An interactive wavelet program was designed using quadrature mirror filters developed by S. Mallat. Using the bandpass representations of the signal, BVI noise was isolated and extracted from the overall helicopter noise signature. Future research will integrate the wavelet decomposition into an adaptive frequency domain controller for BVI noise minimization.a)With NASA Ames Res. Ctr., MS T-42, Moffett Field, CA 94035.
A comparison of elastic constants of the quasicrystalline and cubic approximant phases of AlCuLi, using resonant ultrasound spectroscopy
Authors: Spoor P. S. , McKenna M. J. , Maynard J. D.
Published: October 2005

The anisotropy ε=‖1−2c44/(c11−c12)‖ of a sample of quasicrystalline (T2-phase) AlCuLi has been measured in our laboratory to be 0.0020±0.0004; since a perfect quasicrystal should be isotropic, this could signify deviation from perfect icosahedral order. A comparison with the closely related R-phase cubic approximant, which is often present when macroscopic quasicrystals are grown, may provide a better basis for interpreting such measurements. Among the various methods of determining elastic properties, only resonant ultrasound spectroscopy, which uses the normal mode resonance frequencies to retreive the complete elastic tensor in one measurement, offers the necessary sensitivity to resolve such small anisotropies. Results on a recently received R-phase sample, and on its neighboring icosahedral grains, will be compared with the results mentioned above. [Work supported by NSF Grant No. DMR-9000549 and by the Office of Naval Research.]
Using piezoelectric film and resonant ultrasound for photoacoustic measurements of very low optical absorption in piezoelectric and dielectric crystals
Authors: McKenna M. J. , Lin Wei-Li , Maynard J. D.
Published: October 2005

The photoacoustic effect is one of the most sensitive methods for measurements of the low optical absorption in glasses and crystals. Previously, a new photoacoustic technique has been developed, where a cw laser modulated at the acoustic resonant frequency of the sample generates an acoustic signal amplified by the quality factor of the resonance. With typical quality factors in the order of 105, this technique is several orders of magnitude more sensitive than conventional pulsed-laser techniques. However, previous applications using noncontact capactive transducers required precise postitioning of the sample, transducers, and seperate sample supports. Recently, this difficulty has been reduced through the use of 9-μm-thick piezoelectric (PVDF) film transducers. By supporting the sample at the corners between the film transducers, the need for separate supports is eliminated, with only a small reduction in the quality factor of the resonance. In addition, a large improvement in the signal-to-noise ratio is observed. Recent measurements on large single crystals of calcium floride and quartz will be discussed. [Work supported by NSF Grant No. DMR-9000549 and by the Office of Naval Research.]
Thermoacoustics of traveling waves
Authors: Raspet Richard , Bass Henry E. , Kordomenos John
Published: October 2005

Standard thermoacoustic sources and refrigerators have the stack placed near one end in a standing wave tube. This selection of the stack position optimizes the thermoacoustic effect. For certain applications, however, the effect of a thermoacoustic stack on a traveling wave is of primary interest. Equations governing wave propagation through a thermoacoustic stack have been derived including equations for work flux. When the wave propagates in the direction of increasing temperature, the wave is amplified by an amount dependent upon the temperature gradient. Waves propagating in the opposite direction are attenuated. Counterpropagating waves in a standing wave tube encounter both. In this case, the results reduce to those developed earlier by Swift [J. Acoust. Soc. Am. 84, 1145–1180 (1988)] and others. [Work supported by ONR.]
Transient sound radiation from impulsively accelerated bodies
Authors: Wu Sean F.
Published: October 2005

This paper presents an integral formulation derived from the Kirchhoff integral theorem for predicting transient sound radiation from an impulsively accelerated body. The acoustic pressure is determined in an explicit form in the frequency domain, and subsequently converted to the time domain through Fourier transformations. This integral formulation can be extended to cases in which the body is subject to an arbitrarily time-dependent excitation. The transient acoustic pressure is shown to be expressible as a convolution integral of the impulse response function to the time history of the surface velocity of the body. Since there is no relationship between the integral formulations for the exterior and interior regions, solutions for the radiated acoustic pressure in the exterior region are unique, even at frequencies corresponding to the eigenfrequencies of the related interior boundary value problem. Analytical results based on this integral formulation agree perfectly with those obtained using other methods for transient sound radiation from an explosively expanding sphere, impulsively accelerated rigid sphere, impulsively accelerated baffled and unbaffled circular disks. [Work supported by ONR.]
Acoustic spiral wave field
Authors: Ceperley Peter H. , Koren Alon
Published: October 2005

While most low-amplitude acoustic waves in uniform media can be considered to travel straight from source to receiver, the energy flow and propagation directions in a spiral wave field change as the wave moves away from its source [P. H. Ceperley, Am. J. Phys. 60, 938–942 (1992)]. Thus, one would expect that directional microphones and acoustic imaging systems would give false information as to the location of the source in such a wave field. Two synchronized oscillators, four small speakers, and a horn were used to create a spiral wave in the laboratory. A table top robot arm and microphone were used to map out this sound field, which was then displayed in color using MathCad. The apparent propagation direction was measured using a directional microphone. [Work supported by ONR.]
Monitoring, diagnosing, and actively controlling of complex systems using acoustic signatures and artificial neural networks
Authors: Ünal A.
Published: October 2005

Artificial neural network-based technology enables us to monitor complex systems in real time with reasonable efficiency. Acoustic signatures and/or their transforms can be utilized for diagnosis with less false alarms by exploiting the robust feature extraction abilities of the artificial neural nets. Active controlling requires the instantaneous sensing and actuating abilities that cannot be obtained otherwise. Only the use of artificial neural nets enables us to annihilate the excessive vibrational fields in complex systems. Examples from real life will be given.
Training and representation issues in machine diagnostic by neural networks
Authors: Sayegh Samir I.
Published: October 2005

Neural networks have emerged as a viable and effective paradigm for pattern recognition and discrimination. A widely used algorithm, backpropagation, can be sensitive to the representation used for the input patterns to the network. This is particularly true in machine diagnostic. An application is presented to discrimination of good versus bad electric motors. Representations in terms of spectral coefficients, wavelets, and KL coefficients are contrasted.
Application of multiresolution decomposition to scattering
Authors: McCoy John J. , Steinberg Ben Zion
Published: October 2005

The theory of multiresolution decomposition, using orthogonal wavelets, has received considerable attention as a tool for signal processing and more recently for developing efficient numerical algorithms for the solution of a class of integral equations. Relatively few studies have been reported of its use to investigate fundamental physics of the across-length-scale coupling that is a critical component for understanding the response of complex dynamical systems. In the context of the scattering of acoustic signals by a complex subscale heterogeneity in an elastic plate, the accommodation of the subscale heterogeneity in prediction models for the full-scale response, via a precisely defined operator, is demonstrated. This operator is seen to be invariant under changes in either the problem forcing or in the full-scale geometry of the plate system.
The multiscale structure of the passive scalar field in turbulent water jets
Authors: Everson R. M. , Sreenivasan K. R.
Published: October 2005

The wavelet transform is applied to two-dimensional dye concentration data in axisymmetric turbulent jets at moderate Reynolds numbers. The transform permits an examination, at different scales, of the geometry of turbulent structures. Information about the number of structures at a given scale, their area and aspect ratio is obtained; long, stringy structures are observed at small scales in contrast to the short, rounded structures at large scales. The wavelet transform is also applied to temporally resolved sequences of laser-induced fluorescence images, which allows analysis of the evolution of structures at different scales, their interactions, and speeds. It is found that a significant part of the dynamics involves the merging of scales besides the usual splitting traditionally associated with cascading. Furthermore little coupling between structures at different scales is observed. A comparison with the vorticity field is made.
Nonlinear and robust signal extraction based on wavelets
Authors: Bruce Andrew G. , Donoho David L. , Martin R. Douglas
Published: October 2005

The wavelet transform is an important new tool in applied mathematics, engineering, and science. In a series of papers, Donoho and Johnstone (1992) develop a powerful theory based on wavelets for extracting nonsmooth signals from noisy data. Several nonlinear smoothing algorithms are presented that provide high performance for a wide range of spatially inhomogeneous signals. These algorithms are computationally very fast. However, like other methods based on the linear wavelet transform, these algorithms are very sensitive to outliers in the data. The effect of a large isolated observation on the wavelet transform is smeared through all wavelet scales. In this paper, outlierresistant wavelet transforms are developed. In these transforms, outliers and outlier patches are localized to just a few scales. Hence, it is easy to identify and remove the outliers. By using the outlier resistant wavelet transforms, the Donoho and Johnstone nonlinear signal extraction methods are improved upon. These algorithms prevent outliers from leaking into the extracted signal. Applications will be given for a variety of data sets, including ocean acoustic data (e.g., ice cracking) and glint noise. [This research is supported by ONR Contract No. N00014-92-C-0066.] a)Also with Department of Statistics, University of Washington, Seattle, WA 98195.
Ambient noise oceanography: A new remote sensing technique for shallow water
Authors: Buckingham Michael J. , Deane Grant B.
Published: October 2005

Ambient noise contains broadband information about the oceanic environment. In particular, in shallow water, because of the multiple boundary interactions, ambient noise contains information about the geoacoustic parameters of the bottom. To extract this information, it is necessary to identify stable, reliable features of the noise. (Noise intensity is neither stable nor reliable since it is influenced by numerous highly variable factors.) An example of a reliable feature of the shallow-water noise field is its vertical directionality, which is controlled by the bottom. In fact, in an isovelocity channel of uniform depth overlying a fast fluid bottom, the vertical structure of the noise can be inverted to obtain an accurate estimate of the sound speed in the bottom sediment [Buckingham and Jones, J. Acoust Soc. Am. 81, 938–946 (1987)]. Thus, in this example, a simple measurement of the vertical coherence of the noise in the water column yielded an important geoacoustic parameter of the sediment. Similarly, in shallow water overlying a sloping, penetrable bottom (i.e., a range-dependent channel supporting three-dimensional acoustic propagation) the noise shows a horizontal anisotropy that could be used to determine geometric and geoacoustic parameters of the channel. In such applications, ‘‘ambient noise oceanography’’ provides a remote sensing tool for interrogating the bottom, much as seismic reflection and refraction techniques are used at present. [Research supported by ONR.]
Considerations for shallow water propagation experiments
Authors: Ewart T. , Henyey F. , Jackson Darrell R. , Thorsos Eric I.
Published: October 2005

When one examines the issues involved in propagation of sound in shallow water, the conclusion is that the ever-present ocean bottom, with its inhomogeneity and anisotropy, will dominate. A single model with a few parameters will not be appropriate for all bottom types. This is unlike studies of scattering in the random ocean volume and from the sea surface, where simply parametrized models are useful. The presence of very large numbers of multipaths blurs the distinction between stochastic and deterministic issues. It is clear that one needs to understand the angular and temporal behavior of the acoustic fields in order to understand the channel characteristics for given source(s)/receiver(s) combinations. This implies that large aperture and broadband experiments will be required. Several issues must be addressed before designing such experiments. (1) Will the present simulation capability allow one to design a good experiment for the case of a reasonably homogeneous bottom? (2) How many multipaths are there, and can they be separated? (3) If there are a large aperature and bandwidth, can matched field or backpropagation methods of source localization work? (4) What are the rest of the questions? This group will conduct an experiment in Knight Inlet, BC, which will include preliminary shallow water measurements, and the plans for this experiment will be discussed.
Geoacoustic modeling of the seafloor—Recent experimental work
Authors: Stoll R. D. , Ewing J. , Akal T.
Published: October 2005

Over the past decade a number of new techniques have been developed for measuring the geoacoustic properties of seafloor sediments. Several of these methods utilize sensors that are deployed on the seafloor and respond to seismic waves generated by different kinds of source including explosives and mechanical impact as well as the ambient pressure fluctuations generated by wave motion at the sea surface. Since the motion that is sensed at the seafloor is a combination of many different kinds of interface and body waves (i.e., Scholte waves, Love waves, p, sv, and sh refractions and reflections, etc.), inversion to obtain a geoacoustic model is a complex task that must be tailored to each individual experiment taking into account the bandwidth of the signal and the interaction between the various types of wave. This paper summarizes some of the recent field experiments and the methods that are being used to interpret the data. [Work supported by ONR codes 1125OA and 1125GG.]
High-resolution shallow water 3-D survey and inversion for geophysical parameters
Authors: Sen Mrinal K. , Stoffa Paul L. , Austin James A.
Published: October 2005

In the shallow water environment even in subsurface depths less than 30 m, 3-D structures can affect wave propagation. A high-resolution (500–3500 Hz) 3-D survey (53 lines; 5-km length, 10-m line spacing, 5-m shot spacing) using a Huntec deep-towed boomer source and STARFIX navigation was carried out offshore New Jersey in 1989. Additional 3-D acquisition along with vibra coring will be conducted in the same region in the summer of 1993. Processing and 3-D interpretation of the data record geologic features hundreds of meters across but only several meters in total depth, i.e., glacial meltwater channels prior to the most recent Wisconsin glaciation. Reducing spatial sampling even to 100-m line spacing results in severe spatial aliasing of these features, making geologic interpretation erroneous. In addition to 3-D structure, local subsurface elastic properties need to be estimated quantitatively by inverse methods. The global optimization methods can be employed to derive earth models and their uncertainties. A major challenge is to combine 3-D acquisition, imaging, interpretation, and core data with the requirements of material property estimation such that a complete understanding of propagation in shallow water environment can be achieved.
Influence of internal solitons on sound propagation in shallow water with a summer strong thermocline
Authors: Zhou Ji-Xun , Zhang Xue-Zhen , Rogers Peter H.
Published: October 2005

Analysis of extensive data has shown that the internal waves in the coastal zone exhibit the properties of solitons. Using experimental data and numerical simulation results, this paper shows what happens to sound propagation if internal solitons are present in shallow water with a strong summer thermocline. The experiments were conducted in the Yellow Sea off the China coast during the summer, where strong thermoclines with more than 10 °C temperature difference are often present. In order to provide a clear physical picture on the true problem, a carefully chosen simple ocean model is used to show the resonant interaction of sound waves with internal solitons, including signal frequency, soliton wavelength, and packet length resonances. Then, the numerical model is extended to include the classic characteristic properties of more realistic ocean soliton packets. Under the resonance condition acoustic mode coupling transfers a significant amount of energy from lower modes into higher-order modes that have much larger attenuation rates. This becomes a new attenuation mechanism for shallow water with a strong thermocline. The ‘‘resonancelike’’ behavior predicted by the PE analysis is consistent with mode coupling theory. [Work supported by ONR and IAAS.]
Shallow water acoustics research issues
Authors: Ali Hassan B. , Field Robert L. , Caruthers Jerald W. , Wagstaff R. A. , Chin-Bing Stanley A.
Published: October 2005

Propagation of sound in shallow water is complicated by the proximity of the boundaries and interferring noise sources and by environmental variability. Moreover, geomorphic and geoacoustic properties of the seabed play a major role in the character of the propagating signal. Propagation prediction is complicated by the need to use full wave field models versus simpler ray models. Roughness and inhomogeneities of the interfaces and seafloor are important to both forward and backscatter. Multiple interactions with the interfaces cause signal frequency, angle, and time spreads, coherence loss, and out-of-plane effects, and they exacerbate shear and interface wave problems. The practical effects of all this are complications in the reverberation and noise fields and in signal coherence. On the other hand, match-field processing in shallow water provides some benefits (essentially, by taking advantage of multiple images of the target reflected in the boundaries), but achieving a positive net gain is critically dependent on our basic understanding of the multiplicity of detrimental effects. These issues are discussed in terms of their relevancy to acquiring this understanding to support ongoing technology and advanced development programs in the Navy.
Modeling issues for predicting sound propagation at moderate frequencies in bottom-limited sound channels
Authors: Tappert Frederick D. , Brown Michael G. , DeFerrari Harry A. , Monjo Charles , Nghiem-Phu Lan
Published: October 2005

Consider sound propagation in the moderate frequency range (depth to wavelength ratio, H/λ, between 20 and 100) in shallow water environments with bottom roughness. Measurements in the Straits of Florida have shown remarkable phase stability together with rapid (minutes-to-hours) unstable amplitude fluctuations that nevertheless yield stable envelopes when averaged over many hours. What physical effects should be contained in an acoustic model in order to predict the observed behavior? It is suggested that a full-wave model that is capable of multiple rough bottom forward scattering and includes temporally slowly varying range-dependent sound-speed profiles will yield observed results, when used together with coherent signal processing techniques. A broadband PE model will illustrate the assertion, at least qualitatively. Absolute level prediction is quite another matter that requires more extensive environmental inputs.
Progress on the development of an instrument standard for the measurement of sound intensity
Authors: Krishnappa G.
Published: October 2005

ANSI and IEC working groups have been involved in the development of instrument standards for the measurement of sound intensity. The primary application of these standards is to instruments used for determining sound power of noise sources in accordance with the requirements of approved ANSI and ISO standards. The approach taken by both the working groups in the development of the documents is very similar with only minor variations, notably in the frequency range, specification of pressure residual intensity requirements, and testing devices. Requirements and performance verifications are specified for the complete instrument system comprising probe and processor, and separately for the probe and processor. Performance verification tests are written in terms of type of tests, periodic verification tests, and field checks. The paper will discuss in detail, the scope and purpose of the standard, instrument requirements, and methods for performance verifications.
Standing wave tube testing of sound intensity probes
Authors: Guy R. W.
Published: October 2005

To ensure correct measurement of sound intensity in highly reactive fields and lower frequencies (≤400 Hz) a standing wave field performance test has been specified in a draft standard (IEC 1043 Instruments for the measurements of sound—instruments which measure intensity with pairs of pressure sensing microphones, Draft Standard 1991). The purpose and requirements of the test are examined from theoretical and experimental perspectives, and suggestions for change are made. It is shown that differing tolerance limits are required if over and underestimate error cases are to be considered. A wider tolerance limit may be specified for the standing wave required by the test and fewer measurements need to be taken (2 in contrast to 15). [Work supported by the National Science and Engineering Research Council Canada—Individual Operating Grant.]
The standardization of sound power determination using sound intensity measurements: An analysis based on a computer simulation
Authors: Laville Frédéric , Nicolas Jean
Published: October 2005

The standardization of sound power determination using sound intensity measurements is a much more difficult task than in the case of pressure measurements. The difficulty comes from the fact that both the precision of each intensity measurement and of the resulting sound power depend strongly on the acoustic field. This effect has been analyzed with a computer simulation that has a broader scope than previous ones that were restricted to the evaluation of the sampling error for the source field only. Because the intensity estimated with two microphones is computed for sources represented by monopole arrays located inside as well as outside the measurement surface, the effects of instrumentation error and background noise field are included. The discrete point measurement standards proposed by ISO and ANSI are critically examined with the computer simulation. Among other results, it is shown how F3 as defined in the ISO standard is a good indicator of the phase mismatch error but should not be used in conjunction with F2 as suggested in the standard at this approach leads to variable error limits. [Work supported by IRSST.]