bluuebunny/crossref_metadata_2025 huggingface dataset:
Relations between the temporal and the prosodic structure of French
Authors: Zellner Brigitte
Published: October 2005

In a text-to-speech system, a well-constructed prosodic grammar is of primary importance. Extensive prosodic components have thus been incorporated into French speech synthesis systems. However, relatively little work has concentrated on factors that control speech fluency [B. Zellner, ‘‘Pauses and the temporal structure of speech,’’ inFundamentals of Speech Synthesis andSpeech Recognition, edited by E. Keller (Wiley, Chichester, 1994), pp. 41–62]. It was hypothesized that the lack of fluency observed in most French synthesizers was mainly due to insufficiencies in their temporal structure. This suspicion originated in the observation that utterance timing was most often inferred from its accentual structure, just as in English. However, French accent structure is known to be dramatically different from English accent structure, which renders this assumption suspect. A temporal model was thus developed, based on psycholinguistic evidence. In this model, no initial accentual information was required, yet it could be added in later processing for the production of local modifications of segment durations. First assessments of the model are promising, in view of a highly observed correlation between synthesized and natural speech with respect to measures of syllabic duration.
TEMAS: Visualization of temporal variation in spontaneous speech
Authors: Kitazawa Shigeyoshi , Ichikawa Hideya , Kobayashi Satoshi
Published: October 2005

This study presents a new method for analyzing speech rhythm. First, speech speed is measured and displayed on the basis of syllable (or mora) and stress (rhythmic foot). Then, this specific algorithm TEMAX (temporal evaluation and measurement algorithm by KS) is applied to the speech envelope sampled at 40 Hz; speech wave is half-wave rectified and low-pass filtered at 20 Hz. The DFT of the envelope using a 1-s window is convenient to set off isosyllabic characteristics. For Japanese, the TEMAX-gram, a sonagraphic output, traces two dark bars, called rhythmic formants: RF1 and RF2: the first one, around 8 Hz, and the second one, at about halfway. RF1 corresponds to speech rate, which appears almost steady in read speech and monolog but shows wide variations in spontaneous speech. RF2 represents the bimoraic rhythmic foot, that is, a combination of two adjacent moras forming a single large power peak. Considering English, its isochronic characteristics are observable with a 2-s window as RF1. Furthermore, using a 1-s window TEMAS-gram displays the periodicity of syllables between stress as broken bars around 5 to 10 Hz. This approach appears to be a promising tool for analysis of extremely different rhythmic structures.
Synthetic aperture matched-field processing
Authors: Lee Yung P.
Published: October 2005

Acoustic synthetic aperture processing (SAP) has been discussed in a special issue of IEEE J. Ocean Eng. [ 17(1) (1992)]. It is noted that SAP essentially converts temporal gain to spatial gain. If one is working in an isotropic noise field and is concerned with the total gain only and not directionality, SAP provides no ‘‘new’’ gain. However, in the case of a nonisotropic noise field, one can achieve much larger spatial gain from SAP at the expense of temporal gain. To achieve this larger spatial gain, one needs to maintain the signal and null out the directional noise. A major problem in maintainng the signal in SAP is that the signal can be degraded due to propagation perturbation resulting from multipath interference. To overcome this problem, it is proposed to incorporate matched-field processing (MFP) in SAP. In MFP, a propagation code is used to model the multipath interference and includes it in matched-filtering data. It will reduce multipath signal loss and provide better source localization. To address signal response of the synthetic aperture MFP, data from a 1995 shallow-water experiment were processed and results will be discussed.
Reducing mismatch effects for matched-field processing in a shallow water northeast Pacific Ocean environment
Authors: Ozard John M. , Yeremy Maureen L. , Chapman N. Ross , Wilmut Michael J.
Published: October 2005

This paper describes matched-field processing (MFP) of northeast Pacific Ocean data collected from a vertical line array (VLA) during PACIFIC SHELF 93. In this trial, sound at 45, 70, and 72 Hz from a source at a depth of 30 m towed downslope in water from 150 to 375 m deep was received on a 16-element VLA with sensors evenly spaced between 90 and 315 m. Using sparse bathymetric data, a single measured water sound-speed profile, and estimates of bottom properties, MFP correlations on individual ambiguity surfaces were found to be greater than 0.9 for the strongest signals. By applying an efficient linear tracker to the top 15 peaks extracted from each MFP ambiguity surface at a fixed depth, the source’s depth and range as a function of time were recovered. In contrast, the source position could not be determined unambiguously from most of the ambiguity surfaces. These results show the reduction in ambiguity of source position through the use of an efficient tracker. Results are also presented that show the localization or detection performance improvement from reducing mismatch from array tilt, improving the tracking model, searching for the best bathymetry in an N by 2-D model, and taking mode coupling into account.
Performance estimation for matched-field processing trackers
Authors: Wilmut Michael J. , Ozard John M. , Zala Cedric A.
Published: October 2005

A procedure is presented for estimating the probability of localized detection of an acoustic source under conditions of low signal-to-noise ratio (SNR). This technique, motivated by a tracking application, considers the strongest peaks in the ambiguity surfaces generated by matched-field processing. In an exhaustive series of simulations, conditions were defined under which a Gaussian cumulative distribution function (cdf) predicted the probabilities that a source at a particular location and SNR produced one of the m strongest peaks in the ambiguity surface, for various ranks m. The procedure for efficient performance estimation involved the use of noise-only data to define statistical thresholds for peaks in the ambiguity surface which corresponded to the various ranks. These thresholds could be used to predict analytically the probabilities of localized detection as a function of SNR. Results obtained for slanted and horizontal arrays indicate that this approach, combined with other analysis, can provide an effective way to estimate the probability that the source track is examined and to determine the detection performance and localization accuracy of arrays.
Matched-field tracking (MFT) with experimental data
Authors: Fialkowski Laurie T. , Perkins John S. , Fawcett John A.
Published: October 2005

The ability of matched-field tracking (MFT), a matched-field ambiguity surface summation technique, to track a source as it moves through the experimental region is demonstrated in this paper. The acoustic data are from two experiments: TESPEX 2, off the coast of Australia in 1994; and SWellEX-96, off the coast of California in 1996. Both were shallow water regions. Archival bathymetry and expendible bathy thermographs (XBT) taken during the experiment are used to construct the replicas corresponding to trial source positions in a horizontal plane. Matched-field processing is then used to match the data of a source track to the replicas for the region. MFT takes source motion into account by averaging values from these individual matched-field ambiguity functions corresponding to trial source tracks. This results in a new ambiguity function which depends on four parameters: the horizontal coordinates of the initial and final source position. Generally, the results are plotted as a function of the two horizontal coordinates of the final position. As increasing numbers of individual ambiguity functions are included, the movement of the source becomes apparent. The technique shows robustnesss to the uncertainties in replica computation (due to various mismatch problems) and periods when the signal to noise ratio is low.
Matched-beam processing: A synthesis of conventional beamforming and matched-field processing
Authors: Yang T. C. , Yates T.
Published: October 2005

Conventional beamforming, based on the concept of delay and sum of plane-wave signals, has been the cornerstone for radar and underwater acoustic array processing for many years. Matched-field processing, which has received much attention in recent years, represents a departure from conventional beamforming in that the signal propagation is an integral part of the processor. In this paper a framework is presented (i.e., matched beam processing) in which conventional beamforming and matched-field processing can be unified and treated on an equal footing. Matched-beam processing is matched-field processing in the beam domain. The resulting benefits are (1) the extension of full field processing to conventional beams, (2) the ability to do spatial filtering based on the angle of arrival, and (3) the ease of integration of the (matched-beam) processor into existing systems. For a horizontal array in shallow water, conventional beamforming would be the processor to use, but it suffers from signal gain degradation and bearing bias when the signal energy is split over many beams. Matched-field processing can be used to estimate the bearing accurately, but it must simultaneously estimate the target range, depth, and bearing. Using matched-beam processing, bearing can be estimated accurately while maintaining some tolerance to environmental mismatch.
Detection improvements of active sonar processing: Accounting for time dispersive properties of medium in the matched-filter replica
Authors: Michalopoulou Zoi-Heleni , Porter Michael B. , Stergiopoulos Stergios
Published: October 2005

Matched filtering is an optimum detection process when the only difference between the transmitted and received signals is an additive Gaussian noise component. In practice, however, multipath and time dispersions in either deep or shallow water cause energy spreading that distorts the transmitted signal of an active sonar and this results in a loss of matched-filter processing gain [J.-P. Hermand and W. I. Roderick, IEEE J. Ocean. Eng. 18, 447–465 (1993)]. Standard ‘‘sonar matched filtering’’ ignores the propagation medium effects and is therefore suboptimum. This work investigates how the environmental and geometry parameters of detection problems affect the performance of the standard sonar matched-filter detector. Also, a replica-model-based matched filter is implemented that accounts for the time dispersive properties of the underwater environment by convolving the transmitted active signal with the transfer function of the medium. The proposed replica-model-based matched filter is an extension of matched-field processing techniques to active, time-domain problems and is an optimum detection processor if the environment and geometry are modeled accurately. The two methods, standard and replica-model-based, are evaluated with the use of receiver operating characteristic (ROC) curves. [Work supported by DREA and ONR.]
The effect of three-dimensional bathymetry on array processor performance
Authors: Baxley Paul A. , Bucker Homer
Published: October 2005

Array processing on underwater acoustic arrays traditionally ignores three-dimensional aspects of acoustic propagation. In shallow-water environments with sloping seafloors, paths of acoustic energy will ‘‘bend’’ out of the vertical plane containing the source and receiver, creating an acoustic field that may be significantly different from that predicted with a two-dimensional propagation model. Consequently, array processors such as conventional beamformers (CBF) or matched-field processors (MFP) may suffer serious localization errors and correlation degradations when arrays are placed in these environments. This study examines the effects of the two-dimensional propagation assumption on array processor (CBF on horizontal arrays, CBF and MFP on vertical arrays) performance when the field is actually three-dimensional. Computer simulations for the ASA benchmark penetrable wedge were used to systematically quantify degradations as a function of wedge angle, water depth, and distance from the array along a cross-slope track. Three-dimensional effects were also demonstrated experimentally for cross-slope source tow data (bottom slope =4–8 deg) recorded on a vertical line array during the fourth shallow-water evaluation cell experiment (SWellEX-4) off San Clemente Island near San Diego. In both cases, localization improvements obtained by incorporating known three-dimensional effects into the matched-field processor were determined. [Work supported by ONR/NRaD.]
Implementation of adaptive processing schemes in active and passive sonar systems
Authors: Stergiopoulos Stergios
Published: October 2005

This paper details the implementation of adaptive processing schemes with near-instantaneous convergence in integrated active–passive sonar applications. The adaptive schemes of this investigation include a generalized sidelobe canceller (GSC), a coherent broadband adaptive algorithm based on a multiple steered covariance matrix and the MVDR method. The effort is part of a major study that includes the design of a generic signal-processing structure which allows the implementation of adaptive and synthetic aperture signal-processing schemes in real-time sonar systems. Application results from synthetic and real experimental datasets show that the adaptive processing schemes of this study provide continuous beam time series at the input of a matched filter and a spectrum analyzer for active and passive sonar applications, respectively. The same set of results demonstrates that the implementation scheme of this study eliminates undesirable adaptive performance degradation effects such as signal cancellation. In addition, the adaptive beam time series have temporal coherence properties equivalent to those of the conventional beam time series. Moreover, their amplitude of correlation with the reference FM signal of active sonars is the same with that of the conventional ‘‘main stream‘‘ schemes, which indicates that the adaptive algorithms have achieved near-instantaneous convergence.
Active, broadband detection and localization of target in an uncertain multipath environment with a horizontal array: An optimum physics-based signal processing approach
Authors: Wazenski M. , Alexandrou D.
Published: October 2005

Active detection and localization of a target using a horizontal array is implemented via optimum physics-based signal processing. This approach provides a robust method of detection and localization by incorporating anya priori knowledge of the physical environment, however uncertain or incomplete. The active return from a target in a dense multipath environment is assumed to be well modeled as the sum of weighted, delayed, and phase-shifted replicas of the active source transmission. These signal model parameters (i.e., the set of weights, delays, and phase shifts) vary as a function of the physical environment. An acoustic propagation model drives the optimum detector by mapping prior descriptions of the physical environment to a stochastic description of the signal model parameters. The optimum processor additionally provides localization estimates in bearing, range, and depth for a horizontal array. Illustrative simulation results will be presented in the form of receiver operator characteristics (ROC). Experimental results are anticipated. [Work supported by Digital System Resources.]
Coherence estimation of shallow-water acoustic narrow-band cw pulsed signals
Authors: Nagel Samuel M. , Meredith Roger W.
Published: October 2005

Different methods for estimating signal coherence from underwater acoustic data taken in shallow water are compared. Specifically, this study details methods to estimate coherence from narrow-band, high-frequency, short pulse length, cw signals that typify the signals used by mine-hunting sonars in shallow-water environments. Due to the short record length of the received pulses, the spectral frequency resolution was poor using classical Fourier techniques. This motivated alternate approaches for the spectral estimation and coherence estimates. The other methods compared are an autoregressive parametric based approach, a harmonic wavelet approach, and concatenation of successive pulses followed by the classical method.
Broadband mine detection and classification—Preliminary results from a set of low-frequency shallow-water experiments
Authors: Kaczkowski Peter J. , Siderius Martin , Luby James C. , Owsley Lane
Published: October 2005

Mine counter measures (MCM) sonars have seen accelerated development over the last few years as Navy interests have shifted into shallow-water operations. To find mines, most MCM sonar technologies use relatively high-frequency and narrow-band signals to produce high-resolution images of the seafloor. Even so, the problem of discriminating between proud mines and similarly sized false targets and of detecting buried mines at ranges of several hundred meters remains very difficult. The Applied Physics Laboratory-University of Washington in conjunction with Arete Engineering and Technologies Corporation-San Diego have been conducting shallow-water experiments with a relatively low-frequency and very broadband (2–20 kHz) sonar. The use of low frequencies permits greater penetration into bottom sediments and very broadband signals mitigate the lack of spatial resolution expected from a narrow-band analysis. A description of the sonar and of the experiments conducted in Puget Sound using mines and minelike false targets will be presented, as well as some preliminary results illustrating the kinds of signal processing approaches that have been developed.
Frequency-dependent classification cues resulting from localized interactions on a target surface
Authors: Kaduchak Gregory , Loeffler Charles M.
Published: October 2005

Much work has been done to extract information about a scatterer by analyzing the spectrum of its echo return. Typical applications rely on phase matched circumnavigations of a surface guided wave (a ‘‘resonance’’ of the structure). The present research incorporates high-frequency scattering mechanisms which interact in a small localized area located about the specular points of a curved surface. The scattering contributions from such mechanisms promptly follow the onset of the specular echo in the time signature and are independent of the backside of the scatterer. The mechanisms presented here include the effects of thickness resonances and ‘‘negative’’ group velocity surface guided waves. It is shown that by temporally isolating the region about the specular return in the backscattered time signature, it is possible to gain information related to the thickness and/or material properties of a scatterer. This is demonstrated both computationally and in experiments involving cylindrical shells and finite surfaces with one- and two-dimensional curvature. The scatterers are constructed from either anisotropic, fiber-reinforced plastics or metals. Experimental results display the ability to probe the thickness of an extended target with high-resolution sonar. [Work supported by ONR.]
Calculation of speech intelligibility using an autocorrelation function
Authors: Shoda T. , Ando Y.
Published: October 2005

In this paper, a new method to calculate Japanese CV monosyllable speech intelligibility (confusion rate) by use of an autocorrelation function (ACF) is proposed. This method is based on the principle of speech information processing in the auditory pathway and the brain. In order to find out the essential part to identify syllables, the head and tail parts of syllables were cut and speech intelligibility tests were conducted. The normalized ACF of the essential part was analyzed. Results show that all syllables may be characterized by the time (τ) and the amplitude (φ) of only the first dip of the normalized ACF. Using this characterization, together with the distance between syllables and the manner of articulation, the monosyllable speech confusion rate may be calculated.
Design of a plane rectangular near-field array with nearby reflective boundaries
Authors: Martin James S. , Rogers Peter H.
Published: October 2005

The problem of designing an array for the generation of a spatially and temporally discrete region of plane-wave uniformity from 2 to 10 kHz is addressed. The problem is complicated by the fact that the array’s dimensions are close to those of the tank containing it. The array lines are oriented horizontally to allow for phase steering in the vertical plane. Each line is comprised of 26 elements with identical real shading sets. The lines are irregularly spaced and loosely supported giving the array the appearance of a venetian blind. Time and frequency domain analysis are used with simple source assumptions to determine the drive signals for the 34 independently addressable lines in the array. The result is a set of frequency-dependent complex shading coefficients which constitute transfer functions analogous to localized wave solutions in radar and ultrasonics. The function of the peripheral elements of the array can be seen, from a time domain assembly of the transmit signal, to be active cancellation for the late energy from the center elements and the surface reflections. Nearby scatterers (tank walls, water surface, and neighboring array transducers) are modeled as image sources of the array. Drive signals are assembled digitally and applied via a system of simultaneously triggered buffers. Good agreement exists between experimental data and model predictions of array performance. [Work supported by ONR.]
Bilingualism: Sign language and English
Authors: Goldstein Moise H.
Published: October 2005

More than 1000 babies with virtually no hearing are born in the US each year. Over 90% have hearing parents. Two extreme approaches to their language acquisition are: (a) They must attain oral language to stay part of their family; further, ASL is so much easier that it inhibits their gaining oral language and should be excluded; (b) given a functional visual system and a nonfunctional auditory system, the infant will learn ASL at the brain’s pace and, as an adult, he/she will choose to be part of the Deaf culture, so English is de-emphasized. Both approaches are flawed. In the age-old battle between the oralists and the manualists, deaf children and their parents are the losers. For some time there has been the hope that technology will yield dramatic breakthroughs in aids for the deaf. It is suggested here that progress may well be made through intensive study of the neurology of language acquisition [Poizner et al., What the Hands Revealabout the Brain (MIT, Cambridge, MA, 1987)] and application of knowledge about bilingualism [F. Grosjean, Life with Two Languages (Harvard U. P., Cambridge, MA, 1987)].
Use of language media for social activities of hearing-impaired persons in Japan
Authors: Kamikubo Emiko , Hiki Shizuo , Fukuda Yumiko
Published: October 2005

This selective use of language media by the hearing impaired in contemporary Japanese society was investigated. The data used in this study were collected from a survey conducted by mailing questionnaires to 1700 profoundly deaf males and females, aged from 20–70, in 1991. Responses to the items regarding the significance of the language media such as oral and manual methods, and conversation by writing were analyzed, with regard to the difference between the responses of both genders. The following results were obtained: (1) According to the category of people with whom they communicated, the rate of use and the rate of effectiveness of each medium were characteristically different; (2) according to the different occasions of the use of language in daily life, use of the language media and their efficiency differed significantly; (3) assistance from sign interpreters and accompanying persons was useful, depending on the occasion; (4) younger subjects showed higher ability in the use of language media than older subjects; (5) females showed higher ability in lip reading; and (6) one-third of the subjects used only one or two of the language media for all the categories of people and occasions.
Perception of prosodic units in native and non-native languages by 4- to 10-month-old Japanese infants
Authors: Hayashi Akiko , Deguchi Toshisada , Kititani Shigeru
Published: October 2005

The present study investigated whether Japanese infants are sensitive to prosodic cues to clausal units in native (Japanese) and non-native (English) languages. Two types of speech samples (child-directed speech) of each language were constructed for use as stimulus materials: Coincident samples were created by inserting 1-s pauses at all clause boundary locations, and noncoincident samples were created by inserting the same number of pauses between words within clauses. Groups of 6- and 10-month-old infants were tested using Japanese samples, and groups of 4- and 10-month-old infants were tested using English samples on the headturn preference procedure. The results showed that only the 10-month-old infants tested on Japanese speech samples demonstrated a significant preference for the noncoincident samples over the coincident samples. These results indicate that very young Japanese infants are not sensitive to clausal units in either language, but they come to be sensitive to clausal units only in their native language before they are 10 months old.
Comparing L2 production and perception: What level of analysis?
Authors: Flege James Emil
Published: October 2005

Very different conclusions might be drawn concerning the relation between production and perception of a second language (L2) if different levels of analysis are considered. A clear dissociation between production and perception exists at a global level of analysis. Non-natives who speak English with a strong foreign accent are able to scale foreign accents in English sentences much like native speakers of English. Other studies have compared the production of subsegmental acoustic properties that are important to phonetic distinctions (e.g., vowel duration differences in English words ending in /t/ vs /d/) to listeners’ perceptual use of the ‘‘same‘‘ property (e.g., stimulus vowel duration as a cue to the identification of a final stop as /t/ or /d/). Such studies typically yield only modest correlations between production and perception. Ultimately, however, it may be most useful to consider the perception–perception relation at a categorical (segmental) level. A recent study tested for phonetic category formation by Spanish/English late bilinguals. Subjects who provided perceptual evidence for having established a new category for English /t/ (which differs phonetically from the short-lag Spanish /t/) produced a robust voice-onset time distinction between Spanish /t/ and English /t/. On the other hand, subjects who had apparently not established an English /t/ category produced English /t/ with Spanish-like VOT values. [Work supported by NIDCD.]
Learning non-native speech contrasts: What laboratory training studies tells us
Authors: Akahane-Yamada Reiko
Published: October 2005

Training studies of the past decade demonstrated that laboratory training can improve the ability of adults to perceive non-native speech contrasts. Those studies used various training methods, which differed in several variables, such as target contrast, task, stimulus material, stimulus sequence, and amount of training. Recently, the effects of these variables have been systematically examined in a series of studies [e.g., Lively et al., J. Acoust. Soc. Am. 96, 2076–2087 (1993); Magnuson etal ., J. Acoust. Soc. Am. 97, 3417(A) (1995); Bradlow et al., Proc. ICPhS, 562–565 (1995)]. When Japanese speakers were trained on /r/–/l/ minimal pairs using an identification task with natural tokens, the effects were generalized to novel talkers and novel words. The following findings were also obtained: First, the training using a single talker sometimes failed, suggesting the importance of high variability in the stimulus set. Second, the training in perception resulted in improvement in production, implying a close link between speech perception and speech production. Third, trainees retained their perception and production ability as much as 3 to 6 months after the conclusion of the training, proving that the laboratory training produced long-term modifications in both domains. Implications for the optimization of this training method will be discussed in the context of theories of perceptual learning and development of phonological categories.
Characterization of PMN-PT-La for use in high-power electrostrictive projectors
Authors: McLaughlin Elizabeth A. , Powers James M. , Moffett Mark B. , Janus Robert S.
Published: October 2005

There is increasing interest in relaxor ferroelectrics such as PMN-PT-La,Ba (lead magnesium niobate-lead titanate doped with lanthanum or barium) for use as high-power transducer driver materials in lightweight projector arrays. These electrostrictive materials have been shown to have induced strains an order of magnitude greater than PZT at modest electric fields. The drawback, however, is that the response of the material is dependent on frequency, prestress, temperature, and ac drive and dc bias fields. To date no measurements have been made of all these relationships for 33-mode vibration applications. In this study, using various mechanical prestresses, quasistatic room temperature measurements were made of the piezoelectric constant, d33, of the relative permittivity, ε33T/ε0, and of the short-circuit Young’s modulus, Y33E for PMN-PT-La (TRS Ceramics, Inc., 0.90 / 0.10 /1%, 31 March 1995). Electric fields of up to 2 MV/m were applied to samples (2×2×10 mm that were prestressed from 0 to 12 ksi (83 MPa). The material was found to have energy density values comparable to Terfenol-D, but its lower electromechanical coupling may compromise the useful bandwidth. [Work sponsored by the Office of Naval Research.]
A new one-dimensional model for electrostrictive materials
Authors: Robinson Harold C.
Published: October 2005

Electrostrictive materials such as lead magnesium niobate (PMN) are currently being evaluated for use in high-powered sonar transducers and actuators. The principal characteristics which differentiate them from piezoelectric ceramics are nonlinear dependence of the strain on the applied electric field and saturation of the polarization at high electric fields. A new set of constitutive relations for the behavior of electrostrictive materials in one dimension is developed, using the stress and the electric field as the independent variables. These relations are derived from a Gibbs free energy function using thermodynamic definitions of the strain and the electric displacement. The nonlinearity of the strain and the saturation behavior are included explicitly in the formulation. The resulting equations reduce to the correct power series forms for a pure electrostrictor [G. H. Blackwood and M. A. Ealey, Smart. Mater. Struct. 2, 124–133 (1993)] in the limit of small fields and/or stresses. The theory will be shown to be consistent with experimental data on PMN obtained at NUWC. Comparisons with other electrostrictive material models, such as those using polarization as the independent variable [C. L. Hom and N. Shankar, J. Intell. Mater. Syst. and Struct. 5, 795–801 (1994)], will also be made.
New mica-based capacitance ultrasonic immersion transducers
Authors: Bashford Andrew G. , Hutchins David A.
Published: October 2005

A new type of ultrasonic immersion transducer has been designed and constructed that has a wide bandwidth when used in water. It is a capacitive (electrostatic) device, using a micromachined backplate and a thin mica metallized membrane. It will be demonstrated that the field pattern of the device can be plotted experimentally using a miniature hydrophone, and the results will be compared favorably to theoretical predictions. The device has been produced as a plane piston, and also as a focusing device using both an annular transducer and a zone plate. The device has none of the ringing associated with piezoelectric devices, and hence is suitable for a wide range of applications.
Fabrication of an ultrasonic probe using plate-mode waves
Authors: Wakatsuki Naoto , Mizutani Koichi , Nagai Keinosuke
Published: October 2005

Propagation characteristics of plate-mode waves in a wedge-shaped piezoelectric ceramic plate are described based on numerical and experimental results. Distributions of phase velocity, group velocity, and mechanical displacement are given as functions of the product of frequency F and substrate thickness D. In the experiment, the transition wherein the Rayleigh-mode wave disperses into zeroth-order antisymmetrical and symmetrical modes as it propagates on the wedged substrate is studied. The process in which the waves of these modes are reflected from the front end of the substrate and then degenerated again into the Rayleigh-mode wave is also observed and analyzed. By use of the above-mentioned characteristics, a contact ultrasonic probe is proposed which can distinguish between longitudinal and transverse vibrations. In contrast to a probe which uses a convergent beam, this probe has a resolution which is not limited by the wavelength, so it has high resolution even at low frequencies. It is confirmed experimentally that the probe can discriminate longitudinal and transverse vibrations and that it has a resolution higher than about 4 mm, which is the wavelength of a carrier wave around 1 MHz.
A low-frequency directional flextensional transducer and line array
Authors: Butler Stephen C. , Butler John L. , Butler Alexander L. , Cavanagh George H.
Published: October 2005

A unique low-frequency (900 Hz) Class IV flextensional transducer which produces enhanced far-field pressure on one side and canceled far-field pressure on the other side has been developed. The transducer radiating surface consists of an elliptical aluminum shell and a piezoelectric stack along its major axis with two active sections and one inactive section. The directionality is achieved by exciting the shell into an omnidirectional and dipole operation by driving the ceramic stack into both extensional and bending modes. Both measurements and modeling on this device show a front to back pressure ratio of more than 25 dB, producing cardioid type radiation patterns over an octave band. The measured mechanical Q, coupling coefficient, and electroacoustic efficiency were found to be approximately 8%, 0.25%, and 80%, respectively, and the transducer produced a source level of 215 dB re: 1 μPa/m. Six of these transducers were placed in a closely packed line array. The array successfully produced narrow directional sound beams with a front to back ratio greater than 25 dB and a source level of 225 dB re: 1 μPa/m. [Work supported, in part, through a U. S. Navy SBIR contract.]
A nonacoustic reference sensor for processing against turbulent flow noise
Authors: Bruno Anthony B. , Kasper Rolf G. , McDowell Donald J.
Published: October 2005

Hydrophones embedded within conformal, towed, and free-falling arrays are subject to a noise contribution due to the turbulent boundary layer flow that exists over the array’s external surface. At medium to high flow speeds, this noise can dominate the arrays output to the extent that detection and/or localization of targets is improbable. If an independent estimate of the flow noise is available, then extracting the acoustic signals of targets from the flow noise background can be accomplished using standard signal processing techniques. A new sensor, a flush mounted hybrid detector consisting of a permanent magnet, a pair of orthogonal electrodes, and a coincident hydrophone will be shown to act as a reference sensor. The magnetic field of the permanent magnet interacts with the turbulent flow to generate an electric field that is measured by the electrodes. The voltage induced in the electrodes is proportional to the strength of the turbulent boundary layer flow and is thus an independent estimate of this noise. Experimental evidence will be shown demonstrating coherence between the electrode pair and a coincident hydrophone.
Estimation of the the direction-of-arrival of the sources and the cross-spectral matrix of the noise without eigendecomposition
Authors: Bourennane S. , Frikel M.
Published: October 2005

In the context of the narrow-band or wideband array processing problem, in this study a robust method is developed to improve the accuracy of the estimation of the direction-of-arrival of the sources. It is well known that when the noise cross-spectral matrix is unknown, these estimates may be grossly inaccurate. Using both a least-squares algorithm and a noneigenvector algorithm to estimate the noise subspace projection matrix and then its corresponding eigenvalues using the Rayleigh quotient, a new robust algorithm for the source characterization problem in the presence of noise with an unknown cross-spectral matrix is developed. It is shown that the performance of bearing estimation algorithms improves substantially when the robust estimate is used. Simulation results are presented for the Toeplitz band noise spectral matrix model.
Wind-dependent sea noise in open and enclosed waters
Authors: Cato Douglas H.
Published: October 2005

Because of low shipping densities and thus low traffic noise in some of the waters around Australia, ambient noise measurements often show evidence of wind dependence at low frequencies. Significant differences, however, have been observed between open oceanic waters and enclosed or partially enclosed waters, in the behavior of noise as a function of wind speed at low frequencies (less than 200 Hz). In enclosed waters, the wind-dependent noise spectrum is similar to that of Wenz [G. M. Wenz, J. Acoust. Soc. Am. 34, 1936–1965 (1962)], having a broad peak at about 500 Hz. In open waters, there is also evidence of a second component that is dominant at low frequencies, significantly exceeding the level of the ‘‘Wenz’’ component at these frequencies. This difference has been observed for similar water depths. One difference between the open and enclosed waters is the absence of swell in the enclosed waters, due to the limited wind fetch. The differences in wind-dependent noise may be related to differences in the behavior of wave breaking and bubble clouds as a result of the presence or absence of swell.
Spatial correlation of noise in underwater acoustics
Authors: Frikel M. , Bourennane S.
Published: October 2005

In eigenstructure methods for direction of arrival estimation of signal wavefronts, the additive noise term is assumed to be spatially white or known to within a multiplicative scaler. When the noise is nonwhite but has a known cross spectral, the problem can still be handled through pre-whitening. However, there are no techniques presently available to deal with completely unknown noise fields. In this paper, the localization of the wideband sources is studied when the noise cross-spectral matrix is an unknown banded matrix. The focusing operator developed in the literature, which is used to estimate the coherent signal subspace, is studied in the presence of spatially correlated noise. Some computer simulations are provided to illustrate the results.
A predictive model for underwater noise level variations with an application to the fracturing of sea ice
Authors: Lewis James K. , Stein Peter J. , Euerle Steve E.
Published: October 2005

A model of the thermal fracturing of the sea is coupled with a model of acoustic propagation in ice and the underlying water to provide a means of predicting underwater noise variations with time. Numerical simulations using the ice-fracturing model provides a time history of the number of fractures per time step, as well as the location of the fracture relative to the surface of the ice. An analytical model is presented that relates such fracturing within an ice floe to noise levels at a given frequency in the water column under the ice. This model accounts for temporal and spatial variations of the elastic modulus of the ice. The analytical solution predicts that most thermally induced, under-ice noise at 500 Hz is a result of fracturing occurring between 5 and 25 cm below the ice surface for a 1.6-m-thick piece of sea ice. When used in conjunction with the fracture time histories determined by the rheological model, the under-ice noise levels predicted by the analytical solution compare quite well with noise observations in the eastern Arctic Ocean.
Breaking wave noise measurements at frequencies below 400 Hz
Authors: Schindall Jeffrey A. , Heitmeyer Richard M.
Published: October 2005

A sea surface noise experiment was conducted in shallow water (200 m) near San Clemente Island in March/April 1995 using a vertical array deployed from the RP/FLIP. Measurements of the time-frequency structure of the noise generated from individual breaking waves were obtained using the endfire beam of a vertical array along with optical measurements of the locations, sizes, and lifetimes of those breaking waves. Strong acoustic bursts in time coincidence with the larger breaking wave events were observed. There is no apparent correlation between the smaller breaking wave occurrences and low-level acoustic noise at the sea surface in this frequency band. These acoustic measurements were the first at-sea measurements capable of spatially resolving the individual breaking wave contributions at frequencies below 400 Hz where collective bubble oscillations are believed to be the dominate sound generation mechanism.
Relation between ambient noise and wind speed at several shallow-water sites
Authors: Smith Randall W.
Published: October 2005

The relationship between omnidirectional ambient noise measurements and wind speed has been investigated at several shallow-water sites. For the sites included in this analysis, water depths varied from about 80 to over 1200 m. Both curve fitting and conditional sampling have been used to reveal the correlation between noise level and wind speed. Other factors that played a role in determining the observed wind speed dependence were the local shipping density and transmission loss characteristics. For the sites included in this analysis, estimated shipping densities varied from almost zero to as high as 27 ships per square degree. The discussion will address the effects of water depth, shipping density, and transmission loss at each site.
Project Spinnaker: Long-term Arctic ambient noise measurements
Authors: Sotirin B. J.
Published: October 2005

Due to harsh environmental conditions, long-term, real-time Arctic ambient noise is extremely difficult to acquire. Since 1988, U.S. and Canadian investigators have been collecting data from temporary ice camps in the Lincoln Sea, northwest of Greenland. During the spring of 1996 a joint U.S./Canadian multiple-aperture, bottom-mounted acoustic array was deployed in the Lincoln Sea under the Arctic sea ice and fiber-optically cabled back to shore over 100 miles away. The data is being recorded in real time and the system is batteried for a 3- to 5-yr life. These data will support many aspects of noise characterization including noise statistics, seismic content, ice signatures, and marine mammals as well as contribute to global scale acoustics and ocean parameter estimation. A brief history of the U.S. technology development, the resulting array configuration and status, and the data analysis, archiving and dissemination plan will be presented. [Work supported by ONR and SPAWAR.]
When does the vertical directionality of the ambient noise exhibit a notch near the horizontal direction?
Authors: Yang T. C. , Yoo Kwang
Published: October 2005

The acoustic environment is known to influence the vertical directionality of the ambient noise. For example, in shallow water with a downward refractive (summer) sound-speed profile, the noise vertical directionality is expected to show a deep (≳5 dB) null in the horizontal direction for wind generated noise below 1 kHz. This ‘‘horizontal null’’ is a consequence of the fact that low-order modes are weakly excited by the noise sources which are located near the ocean surface. This phenomenon has been experimentally observed in limited cases. This paper concentrates on a quantitative analysis of when the vertical directionality will exhibit a notch in the horizontal direction. The answer will depend on the acoustic frequency, the sound-speed profile, the water depth and bathymetry, the bottom properties, the vertical array aperture, and finally the noise source distribution. Currently no simple way exists to model the noise notch except to run the numerical noise model repeatedly. A modal analysis is presented of the ambient noise directionality with a closed-form expression that allows one to predict and model the noise notch under a typical condition.
Low-frequency ambient sound in the North Pacific
Authors: Curtis Keith R. , Howe Bruce M. , Mercer James A.
Published: October 2005

In an effort to quantify the long-term statistics of ambient sound in an ocean basin, data are being collected on 13 SOSUS receivers in the North Pacific. The present data set is over a year long and consists of power spectra from single hydrophones computed every 5 min from 5 to 500 Hz in 1-Hz bands. The clearest feature in many of the spectrograms is a strong seasonal cycle in the 15- to 20-Hz band with peak-to-peak amplitudes up to 25 dB. This is attributed to the presence and the migration of blue and fin whales. Probability statistics as a function of frequency show that the 10% probablity sound level is typically 3–5 dB above the median level, and the 1% level is 10 dB higher. The records have been broken into three frequency bands for further analysis: 17 Hz (whales), 30–100 Hz (shipping), and 200–400 Hz (wind-generated sound). Only for the first band is there significant correlation between arrays. There is no correlation between the high-frequency band and ECMWF estimated wind speed at a receiver location. There is no obvious seasonal cycle in the 200- to 400-Hz band. [Work supported by ONR.]
HOTWIT: An unconstrained shallow-water reverberation estimation algorithm
Authors: Newcomb J. , Bradley Marshall , Walrod Melanie H.
Published: October 2005

A new algorithm/method for the inversion of activated towed array reverberation data in shallow water, known as the heading optional transformation of Wagstaff’s iterative technique (HOTWIT), has been developed. By taking advantage of the activation and motion of the towed array, the algorithm resolves the inherent left–right ambiguity of the towed array without the need for multiple headings and is an active analog to the passive 3-D WIT algorithm. The result is an unambiguous estimate of bottom target strength from which the reverberation density at a given receiver location can be inferred. The algorithm lends itself well to a rapid characterization of shallow-water reverberation in shallow-water areas. A description of the algorithm with a discussion of results from the algorithm with measured and modeled towed array data will be discussed.