bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability in the bearing and range estimates of acoustic sources in air
Authors: Ferguson Brian G. , Criswick Lionel G.
Published: October 2005

When a passive acoustic system is used to localize a stationary sound source in air, the bearing and range estimates are observed to vary, although the source–receiver configuration is fixed. The variability in the estimates of the localization parameters is ascribed to temporal and spatial fluctuations in the sound propagation medium. This experiment employs a wavefront curvature technique to measure the bearing and range of a broadband acoustic source. The technique relies on three equally spaced microphones whose outputs are cross correlated to produce estimates of the differential time-of-arrival of an acoustic wavefront at each pair of adjacent sensors. Three intersensor separation distances are used: 25, 50, and 100 m. The temporal variations in the bearing and range estimates are presented together with an estimate of the measurement precision. Finally, the magnitudes of the systematic errors in bearing and range (introduced by a nonstationary atmosphere) are discussed.
A synthetic aperture parametric sonar for buried object detection
Authors: Fioravanti Stefano , Maguer Alain , Lovik Arne
Published: October 2005

This paper describes an experimental comparison between a parametric sonar and a conventional sonar for the detection of small objects on the seabed. First, a quick description of the parametric sonar used is given. Second, rail and sea experiments are described. The parametric array was mounted on a rail which was able to move at a constant speed (0.25 m/s). As a first experiment the sonar was kept fixed on the rail. A comparison of the detection of the object put on the seabed is performed between conventional sonar and the parametric one. The obtained results show a great improvement brought on by the parametric sonar which is less affected by bottom reverberation and which allows very precise identification of the detected object. As a second experiment, the sonar was moving on the rail in order to be able to perform synthetic aperture sonar processing with the parametric array. Significant improvements in resolution and signal-to-noise ratio were obtained when integrating together successive pings transmitted while the sonar was moving. In addition, a similar experiment performed at sea with a towed fish is described and results are given.
Focusing borehole time–space arrays
Authors: Ekstrom M. P. , Randall C. J.
Published: October 2005

The borehole sonic measurement in well logging consists of a wideband acoustic source operated in ‘‘pitch–catch’’ mode with an offset, linear array of receivers. The source/sensor configuration is moved up the borehole axis at a more-or-less constant speed, and the source fired at depth intervals of approximately one receiver spacing, generating a set of array measurements at each depth. The array processing problem is that of estimating the depth-dependent slowness dispersion of individual modes in the received wavefield. The classical approach to slowness estimation has involved processing each shot array individually, generating a sliding estimator window. The aperture of this measurement is defined by the linear extent of the receiver array. When logging subsurface formations comprised of closely spaced layers, it is often of interest to improve this ‘‘intrinsic’’ spatial resolution. A new two-dimensional spectral estimator has shown to be effective for dispersion estimation using single-shot data sets [M. P. Ekstrom and C. J. Randall, J. Acoust. Soc. Am. 98, 2867(A) (1995)]. In this paper, this estimator is extended to hi-spatial resolution logging. The array aperture is ‘‘focused’’ to improve vertical resolution by exploiting the measurement redundancy available with multiple, contiguous shot files. Examples of processing-field-acquired data sets will be presented.
Short-time Fourier transform: Error estimation with nonstationary signals
Authors: Burgess John C.
Published: October 2005

When used with nonstationary signals, a discrete Fourier transform (DFT or FFT) can provide only approximate values for the spectrum of the true, underlying signal. The purpose of this presentation is to provide some insight into the magnitudes of errors to be expected with increasing nonstationarity and noise, with some hints about how to ‘‘manage’’ the errors. [Work supported by the National Research Council (Canada) and the Lanikai Foundation.]
Line extraction from sonar images of elastic objects
Authors: Chang Min-Fon , Loeffler Charles M. , Kaduchak Gregory
Published: October 2005

Acoustic imaging of elastic targets often results in linear flashes in the image. Delineating these target features could be used in subsequent target detection and recognition schemes; however, the difficulty in this task is not to be underestimated due to the presence of background reverberation or ambient noise in the sonar image. A powerful line-fitting algorithm which locates the linear flashes in sonar images of elastic objects is presented. The algorithm initially groups the image pixels into neighboring clusters by using the parameters of an intensity-weighted least-mean-squared line fit locally computed over the entire image. The algorithm uses the information of these groups in order to extract the dominant lines from the image. It is noteworthy to realize that compared to the majority of line and edge detection schemes, the algorithm actually parametrizes for each line extracted its length, orientation, location, and intensity. By culling these lines based on their parameters, particular linear target features may be emphasized. Applying the algorithm to images produced from experimental high-frequency sonar data has shown that it performs even in consideration of acoustic noise.
Space-time signal processing algorithms for moving antennae
Authors: Gorban Igor I.
Published: October 2005

For underwater acoustic systems, new space-time signal processing (STSP) algorithms have been developed and researched. They realize the maximum likelihood STSP in complex conditions. These algorithms take into consideration a complicated antenna’s motion in space, the particularities of the additive noise, and the properties of the medium together. It was assumed that the antenna moved in three dimensions with variable velocity and angle rotations, the noise was multicomponent Gaussian space-time correlated, and the medium was inhomogeneous. The algorithms were obtained for two types of signals: partially coherent and stochastic ones. The signal-to-noise ratio was calculated and compared for different systems and work conditions. Optimum, some near optimum, and nonoptimum STSP systems were studied. As a result of research it was found that ignoring the fact of the antenna’s motion and the local noise component, often led to a significant loss in noise immunity of STSP systems. In some cases, a complicated antenna’s motion plays a positive role and assists in the rising of noise immunity. This effect may be used in different systems, in particular, in the systems with towed arrays for alienating ambiguity in estimation of signal direction.
Monitoring microseismicity in the northeast Pacific using hydroacoustic techniques
Authors: Fox Christopher G. , Dziak Robert P.
Published: October 2005

On 29 August 1991, NOAA/PMEL began collecting ocean acoustic signals from the U.S. Navy’s Sound Surveillance System (SOSUS) in the northeast Pacific Ocean. SOSUS consists of linear arrays of underwater hydrophones deployed on the seafloor within the sound channel that are directly cabled to shore. The NOAA/PMEL-developed system digitizes the acoustic signals directly from the underwater cables and passes the information via the phone line to NOAA laboratories in Newport, OR for analysis. The hydroacoustic method allows small submarine earthquakes (mb≳1.8) to be routinely detected and located throughout the North Pacific. The primary advantages of this method are the large areal coverage from relatively few sensors and the low detection threshold and improved accuracy of the derived epicenter locations relative to land-based systems. Several significant discoveries have been made using the hydroacoustic method over the past 5 years, including (1) a better understanding of the distribution of seismicity in the northeast Pacific; (2) detection of volcanic activity and magma dike injection supported by extensive field observations; (3) detection of periodic volcanic tremor; and (4) the discovery of a band of low-level seismicity within the Gorda plate that may offer a precursor to subduction zone earthquakes.
T-wave source level and earthquake fault parameters: Empirically derived scaling relationships
Authors: Dziak Robert P. , Fox Christopher G. , Slack Philip D.
Published: October 2005

Since 1991, NOAA/PMEL has routinely detected Tertiary waves from NE Pacific ocean earthquakes using the U.S. Navy’s SOSUS hydrophone arrays. Tertiary (T) waves are seismically generated acoustic waves (between 5–50 Hz) that propagate over great distances in the oceanic sound channel with little loss in signal strength. Low attenuation, combined with the availability of detailed ocean acoustic velocity models, have made T waves extremely useful for monitoring seafloor earthquakes;T waves allow for highly accurate epicentral locations, and a reduction of the detection threshold by almost two orders of magnitude. However, it is still not well understood how seismic energy generated at the earthquake source propagates through the seafloor–ocean interface and couples to the sound channel. Hence, the relationship between earthquake source parameters and the T-wave amplitude recorded at the hydrophone are not directly known. The goal of this paper is to empirically compare earthquake magnitude, seismic moment, and fault orientation (radiation pattern) to an event’s T-wave source level to see if systematic relationships exist. T-wave source level is estimated by deconvolving instrument gain and the transmission loss from the T-wave signal, thus resulting in the earthquake’s acoustic energy at the seafloor–ocean interface.
Periodic deep-sea hydrothermal vent activities observed by hydrophones at Mariana, Okinawa, and Mid-Atlantic Ridge
Authors: Junzo Kasahara , Toshinori Sato , Azusa Nishizawa , Kantaro Fujioka
Published: October 2005

Deep-sea hydrothermal vent activities were studied done by digital OBS/Hs(Ocean Bottom Seismometer / Hydrophone) at three hydrothermal vent areas, the Mariana Trough, the Okinawa Trough, and the TAG area in the Mid-Atlantic Ridge. The OBS/H has three-component seismometers and one hydrophone. The hydrophone has a response from dc to 50 Hz including recording characteristics. The seismometers are made up of one vertical and two horizontal components with a natural frequency of 2 Hz and a response to particle velocity of ground motion. At each location, OBS/Hs were placed at a 1-m distance from nearby fissures or a hydrothermal mound by using submersibles. During a 1-week observation at each location, high-amplitude pulse-like signals were observed only by the hydrophone, but not by seismometers, at all locations. The amplitude of pulses on the hydrophone is extremely large. The hydrophone also recorded numerous natural earthquakes with amplitudes similar to those on seismometers. The appearances of pulses are highly coherent with tide variation. Based on the above results, it is concluded that the tide effect possibly controls the deep-sea hydrothermal vent activities observed as a pressure change.
T-wave detection of underwater volcanism by land-based seismic stations: The example of the Hollister Ridge, Southern Pacific
Authors: Okal Emile A. , Talandier Jacques , Géli Louis
Published: October 2005

Seismic stations close to island shores can record the seismic waves resulting from the conversion of oceanic T waves at the shoreline. Over the past 25 years, the Polynesian Network has detected and monitored a number of active volcanoes on the floor of the Pacific Ocean. Recently, remarkable T waves were recorded from a location in the Southern Pacific (54°S; 140°W); they had both very high amplitudes and exceptionally monochromatic spectra, featuring a single frequency (fluctuating around 8 Hz) throughout the 2–80 Hz range. Other volcanic sources generally exhibit a much richer spectrum, including overtones of any resonance peak. The source of this T-wave activity, 150 km from the Mid-Oceanic Ridge, was explored by surface ships. A massive ridge extending 450 km in length, 20 km in width, and rising to 135 m b.s.l. was mapped. The nature of the monochromatic source remains a challenge. It is speculated that the absence of overtones could be explained by the resonance of a volume of bubbly fluid, significant degassing being allowed by the shallow depths mapped by the ship survey.
Arctic abyssal T-phase coupling to the ocean acoustic channel
Authors: Keenan Ruth Eta
Published: October 2005

Five T-phase events were detected in April 1980 on a horizontal hydrophone array suspended from the arctic icecap at a distance of 300 km from the mid-Arctic ridge. The hydrophone array localized the bearing of the event source and was able to detect P-wave arrivals with 5000- to 8000-m/s phase velocities in addition to the dominant T-phase signature with 1400- to 1700-m/s phase velocities. Scattering from the ice surface is considered as a mechanism to convert the near-vertical seismic energy into propagating acoustic energy. At 5 Hz, the scattering losses are about 40 dB, and at 15 Hz they are about 30 dB. The received acoustic levels of the T-phase spectral peaks ranged from 103–119 dB re: 1 μPa, 1 Hz, and the propagation losses over the 300-km distance between source and receiver are on the order of 90–100 dB. The earthquake source level in the water column is estimated to be about 250 dB re: 1 μPa, 1 Hz at 5 Hz, and 235 dBre : 1 μPa, 1 Hz at 15 Hz. These levels are consistent with refraction measurements of crustal attenuation of 0.52 dB/km at 5 Hz [R. E. Keenan and L. R. L. Merriam, J. Acoust. Soc. Am. 89, 1128–1133 (1991)].
Acoustic array observations of seismic events
Authors: Harris David B. , Hauk Teresa F.
Published: October 2005

Hydrophone arrays may be used to observe continental and oceanic seismic events. Observed signals are of two types: acoustic waves which travel from source to receiver entirely in the SOFAR channel (T-phases), and converted seismic waves, which propagate primarily as elastic waves through the solid earth, but convert immediately beneath the array into vertically traveling acoustic waves. Long-range observations of T phases might be used to identify acoustic blockage. Patterns of T-phase observations at the Nicolas Is. SOSUS arrays for ridge events along the East Pacific Rise and the Pacific-Antarctic ridge are consistent with known areas of blockage in the Tasman Sea and the Chatham Rise. Uncertainty in coupling mechanisms complicate the interpretation of blockage. Hydrophone arrays in the vicinity of continents observe converted seismic waves from on-shore events. An estimate of detection range for events at regional distance is made for selected western U.S. events using several hydrophone arrays in the eastern Pacific. Vertical line arrays improve converted-wave signal-to-noise ratios by enabling vertical beamforming with nulls steered horizontally to suppress ambient noise. [Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]
Monitoring ocean seismicity using autonomous hydrophone moorings
Authors: Matsumoto Haruyoshi , Fox Christopher G.
Published: October 2005

Following the successful use of the U.S. Navy’s SOSUS for monitoring low-level seismicity in the northeast Pacific, NOAA developed a strategy for monitoring remote areas of the world ocean not covered by fixed hydrophone arrays. This strategy requires the deployment of autonomous, hydrophone moorings able to record low-frequency acoustic energy in the SOFAR channel over extended periods. The instrument includes a single ceramic hydrophone, filter/amplifier stage designed to prewhiten the ambient noise spectrum, accurate clock (1 s/yr), and processor modified from off-the-shelf hardware. The instrument is capable of recording at 100 Hz (1 to 40-Hz bandpass) for periods of up to 1 year and is designed to be serviced at sea. A 2-month field test was conducted in the northeast Pacific during May–July 1995 to allow a direct comparison of the method with existing SOSUS arrays and other seismic experiments along the Juan de Fuca Ridge. The results indicate that the sensitivity of the moored systems is comparable to SOSUS detections. In May 1996, the array was deployed in the eastern equatorial Pacific to begin long-term monitoring of the East Pacific Rise between 20N and 20S, the Galapagos Ridge, and the Mid-America Trench.
Modeling oceanic T-phase generation using coupled wave-number-integration approaches
Authors: Schmidt Henrik , Thiam Goh Joo
Published: October 2005

The wave-number-integration approach has traditionally been limited to providing exact solutions to propagation problems in range-independent fluid–elastic stratifications. However, using various coupling approaches, this solution technique has recently been extended to handle stepwise range-dependent problems as well. The spectral super-element approach uses a Galerkin approach to represent the coupling of the wave fields in two consecutive sectors in terms of distributed panel sources [Schmidt et al., J. Acoust. Soc. Am. 98, 465–472 (1995)]. The virtual source approach [H. Schmidt, J. Acoust. Soc. Am. 97, 3316(A) (1995)] solves for reflection and transmission of each wave-number component at discrete points on the vertical sector boundaries, and computes the equivalent distribution of discrete, virtual sources. Both methods then use standard wave-number-integration to compute the resulting two-way seismoacoustic field in the range-independent sectors. This new class of range-dependent, seismoacoustic propagation models provides efficient handling of arbitrary fluid–elastic stratifications and typical oceanic sound-speed profiles. Since these approaches are based on fundamental wave solutions, the environment discretization is dependent on the local environmental length scales only, and they are therefore particularly well suited for modeling seismoacoustic wave field coupling by distinct environment features. The performance of these approaches is demonstrated by modeling the conversion of seismic energy into oceanic T-phases observable in the SOFAR channel. [Work supported by ONR.]
Possible mechanisms for T-phase generation
Authors: Sperry Brian , Goh Joo Thiam , Baggeroer Arthur , Schmidt Henrik
Published: October 2005

Recent extensions to the wave-number-integration approach [Schmidt et al., J. Acoust. Soc. Am. 98, 465–472 (1995) and H. Schmidt, J. Acoust. Soc. Am. 97, 3316(A) (1995)] have made it possible to apply spectral methods to stepwise range-dependent elastic problems. Using these methods, it is possible to study the potential mechanisms of T-phase generation in oceanic waveguides. Such a study has applications in the prediction of tsunamigenisis from T-phase observations. The general environment considered is a canonical sound-speed profile and sloping bottom. The seismoacoustic field is determined via the above spectral methods, and then a modal decomposition is applied. The initial modal excitation and subsequent energy exchange from coupling is examined. The energy that becomes trapped in the water column is indicative of what might be observed on a distant hydrophone. The inclusion of elastic effects in these range-dependent scenarios is likely to be critical in order to fully model the T-phase generation. For a sloping elastic bottom, the lower modes may actually be directly excited by the shear waves, whereas energy injected from compressional waves in the bottom must couple down through the higher modes. The strong presence of low-order modes is consistent with observations. This study considers the importance of a variety of parameters, including slope, source-depth, frequency and bottom characteristics. Both rift and slope bathymetries are considered. [Work supported by ONR.]
Acoustic T-phase directionality measuments using a towed line array
Authors: Chapman N. Ross , Marrett Ralph
Published: October 2005

The directionality of acoustic T-phase signals radiated from a series of shallow undersea earthquake in the South Fiji Basin has been determined using a linear hydrophone array. The array was towed in the vicinity of 24 S 176 W in the northern part of the basin at a depth of 300 m. The T-phase signal from each earthquake lasted for about 5 min, with a maximum level about 2.5 min after the arrival of the initialP -phase event. The T-phase signal directionality was determined by processing the array data using a time-delay beamformer. The first part of the signal arrived on a direct bearing between the earthquake source and the array, but the subsequent stronger components arrived from different directions significantly farther south of the source. A model based on ray path travel times suggests that the later components of the T-phase signal are radiated into the water via downslope propagation from ridges and seamounts. The intitial components are scattered into the sound channel by leakage from the P-phase signal relatively close to the array.
An automated system for detecting and classifying in-water explosions and T-phases
Authors: Laney Hyrum W. , Dysart Paul , Freese Herbert , Willemann Raymond J.
Published: October 2005

In support of the proposed Comprehensive Nuclear Test Ban Treaty, a large database of hydrophone recordings including T-phases, explosions, and noise has been compiled and cross referenced with known seismic events at the Center for Monitoring Research. Using this database, an automated hydroacoustic arrival detection and classification system has been developed. Detection is accomplished with a long-term-average/short-term-average power detector operating in several passbands. Station specific tuning of SNR thresholds and passband bounds allows the detector to trigger reliably on T-phases and explosions while passing over the majority of noise events such as whale calls. For each detected arrival, features such as duration, energy moments, spectral ratio, and order statistics are measured in multiple passbands from 2–85 Hz. A neural network uses these features to classify each arrival as signal or noise. Declared signals are passed to a second-stage network which classifies them as T-phases, explosions, or unknown events. T-phases arriving within a 4-min window around the time predicted from a seismic location are associated with that seismic event. These associations reveal relationships among event parameters such as location, magnitude, depth, duration, and coupling region.
A global monitoring system for a nuclear test ban treaty
Authors: Willemann Raymond J. , Laney Hyrum W. , Dysart Paul , Freese Herbert
Published: October 2005

The rolling text of Conference on Disarmament’s Nuclear Test Ban Treaty requires monitoring by 169 seismic, 11 hydroacoustic, 60 infrasonic, and 50 radionuclide stations. Stations will continuously transmit data to a center for real-time processing. Processing will detect, measure, and classify signals, then it will associate signals at different stations and locate sources. Results will be reviewed by analysis. To prepare, the Center for Monitoring Research participates in a seismic monitoring experiment, which is being broadened to other technologies. Continuous data from hydrophones at Point Sur and Wake Island have been received and processed at CMR since late 1995. Data from additional hydroacoustic stations are imminent. Software for processing seismic data will be adapted for hydroacoustics; real-time detection and feature measurement are underway. Visual review found signals from 30% of shallow, Pacific-region seismic sources in CMR’s bulletin, but the rate varied widely by source region. Among mb≳4.2, h<100 km earthquakes, detection was independent of magnitude and earthquake depth. Ocean depth near the epicenter may control hydroacoustic detection. Differences between visually selected onset times and times predicted from seismic locations and propagation modeling vary widely by region, and are often larger than differences predicted from seismic location uncertainty.
Doubly asymptotic approximations for transient elastodynamics
Authors: Geers Thomas L. , Lewis Brett A.
Published: October 2005

Considerable progress has been made in performing time-harmonic response computations for bodies surrounded by unbounded acoustic fluid and solid media. However, computational impracticality has hindered progress in transient response analysis, which has motivated the development of approximate approaches. A doubly asymptotic approximation (DAA) is an approximate temporal impedance relation at the boundary of a continuous medium; it approaches exactness at both early and late times, effecting a smooth transition in between. Here, first- and second-order DAAs are derived for a uniform, isotropic, elastic medium of either infinite or semi-infinite extent. Following boundary-element semidiscretization, either of these approximations provides a computational boundary for a finite-element model of a ground-shock-excited structure and, if desired, surrounding soil island. The derivations proceed from pertinent singly asymptotic approximations and employ the method of operator matching previously used for acoustic fluid domains. A simple problem with spherical symmetry is considered that illustrates the characteristics of the singly and doubly asymptotic approximations. [Work supported by the Defense Nuclear Agency.]
Trapping of hydroacoustic waves generated by underwater earthquakes into a sound channel
Authors: Lysanov Yury P.
Published: October 2005

Hydroacoustic waves generated by underwater earthquakes in the deep ocean are observed at very long ranges (hundreds and thousands of kilometers) from the place of their generation. This implies that they propagate in the underwater sound channel (USC) without any reflections from the bottom. However, the direct trapping of the acoustic waves is impossible. A physical mechanism of the trapping of waves owing to their scattering from a rough sea surface is investigated. To solve this issue an energetic approach is used. For low frequencies, in the ‘‘single scattering—multiple reflection’’ approximation an expression for the spectral density of the sound intensity is obtained. For numerical calculations a piston model of the earthquake and a ‘‘bilinear’’ model of the USC are used. It is shown that the largest contribution to the sound intensity is given by a weakly divergent bundle of rays. Calculated sound-pressure spectral levels significantly exceed that of the dynamic ambient noise in the ocean for typical values of parameters of the problem. The total acoustic power trapped by the USC is estimated.
Temporal organization in birdsong production
Authors: Okanoya Kazuo
Published: October 2005

Birdsong is a complex time-series behavior that requires learning. Although neural characteristics of the temporal domain in the songbird brain are described in some detail, few studies addressed temporal parameters at a behavioral level. Temporal organization of Bengalese finch (Lonchura striata var. domestica) song in several behavioral paradigms was examined. First, a detailed sequence analysis of song episodes was conducted and a transitional diagram of the song was obtained. Next, ongoing song production was interrupted by a flash-light stimulation, and the pattern of stopping was analyzed. Third, auditory and/or proprioceptive feedback was deprived and the temporal deterioration in the song was analyzed. All data suggest that the song in the Bengalese finch is a hierarchical behavior; a string of produced songs was comprised of subunits. The anatomical and physiological basis of the hierarchical organization of birdsong should be addressed in future studies.
Effect of beak movement in singing Bengalese finches (Lonchura striata var. domestica)
Authors: Moriyama Keiko , Okanoya Kazuo
Published: October 2005

In human vocal production, the lungs produce energy for the voice, the vocal folds have a function of a sound source, and the vocal tract functions as a resonator. Birds have the syrinx for the sound source, but they do not have the vocal folds. In birdsong, the syrinx had been thought to act alone in song production, and vocal tract played no role. However, when a bird sings in helium, harmonic overtones emerge [Nowichi (1989)]. For this reason, it is suggested that the vocal tract may play an important role as a vocal filter in birdsong production. In this study, beam movements were measured in the Bengalese finches while they were singing, and the correlation between fundamental frequencies in the song and the beak gape was examined. This correlation was significantly high (r=0.890), the wider beak gape corresponding to a higher fundamental frequency. The result suggests that in Bengalese finches beak movement formulas a dynamic filter which modifies the frequency composition of the syringeal output. Thus sound production in songbirds may be comparable to that in humans.
Effects of isolation rearing on the development of the distance calls in male Bengalese finches (Lonchura striata var. domestica)
Authors: Yoneda Tomoko , Okanoya Kazuo
Published: October 2005

Distance calls of adult Bengalese finches show sexual dimorphism. The calls of females are widebanded and pulsed, while those of males are narrow-banded and continuous. In an earlier study, it is revealed that this dimorphism appears during ontogeny [Yoneda and Okanoya, J. Ethol.9 , 41–46 (1991)]. Both males and females were emitting female-type calls at an early stage, but male calls begin to show structural changes around day 40–55 and then gradually crystallize into male-type calls until around day 90. In this study, male Bengalese finches were raised normally until day 23 and then isolated from adult conspecifics. The development of the distance calls of these birds was studied. Isolation-reared birds started emitting male-type calls at around day 50–60, but the call remained uncrystallized. It is suggested that the sensory learning of an external model is necessary for establishing crystallized adult male distance calls in Bengalese finches. [Work supported by a Fellowship from the Japan Society for the Promotion of Science.]
A computational model of early stages of dolphin hearing
Authors: Roitblat Herbert L. , Ketten Darlene , Au Whitlow W. L. , Nachtigall Paul E.
Published: October 2005

A computational model of the early stages of dolphin hearing was developed to model dolphin echolocation performance. The first stage consists of a bank of 49 gammatone filters with center frequencies from about 2.5 to 147 kHz. This stage computes the basilar membrane motion that results from the echo time series used as input. The second stage of the model computes a neural activation pattern that rectifies and log transforms the basilar membrane motion and computes lateral inhibition in both frequency and time. The third stage integrates and aligns the neural activation pattern from multiple echoes, a process that has been demonstrated empirically in dolphin echolocation. The result of this processing is a stable auditory ‘‘image’’ or time-frequency map of the signal. The parameters of this model are tuned for the anatomy of the dolphin cochlea. The model has been applied to echo returns from a synthesized dolphin signal reflecting from cylinders in clutter. The cylinders were made of different materials and had an outer diameter of 3.8 cm and a length of 10.2 cm.
Aspect-independent sonar recognition of cylinders using dolphin-like signals
Authors: Au Whitlow W. L. , Shizumura Reid H. , Nachtigall Paul E. , Hicks Robert J. , Roitblat Herbert L. , Moons Gerald
Published: October 2005

Echoes from four different cylinders having the same outer diameter (3.8 cm) and length (10.2 cm) were collected at 1-deg increments from the broadside to the end aspect and used in a neural network recognition study. The water-filled stainless-steel, water-filled aluminum, and foam-filled aluminum cylinders had the same 0.64-cm wall thickness. The fourth cylinder consisted of coral rock pebbles embedded in degassed epoxy. A dolphinlike sonar signal with a peak frequency of 120 kHz and a duration of approximation 50 μs was used in a monostatic echo collection system. Fifty echoes digitized at a 1-MHz rate were collected for each target at each aspect. Time-frequency representation of the echoes along with the envelope of the matched filter response were fed to two parallel independent multilayered feedforward backpropagation neural networks and the results were fused together in another feedforward network. The network was able to achieve better than 90% correct recognition of the echoes when trained with echoes that were separated in increments of 4 deg. Performance dropped to approximately 80% when the network was trained on echoes separated in increments of 10 deg.
A computational model of echo location
Authors: Mitsuhashi Wataru
Published: October 2005

The range and velocity of a moving object were measured unambiguously by a computational model of echo location. Based on the echo-location sounds utilized by some species of FM bats, a linear-period-modulated (LPM) signal was adopted in this model. The LPM signal was designed to yield a phase rotation of π rad for velocity of 0.5 m/s, and its frequency was hyperbolically swept down from 60 to 40 kHz within a 1.4-ms duration time. Experiments were performed in air by changing the velocity of a plastic disk of about 20 mm in diameter. When a passage of the disk was detected by a photosensor installed at a distance of 1 m from transducers, the LMP signal was emitted as a location sound. Echoes were processed by a bank of constant-Q filters, and the range and velocity were estimated according to the temporal phase distribution of phase-sensitive elements connected to the output of each filter. Regardless of the relatively small time–bandwidth product of the LPM signal, results of these estimations show that the estimation accuracy was better than 0.1 m/s in velocity and about 0.5 mm in range. On the contrary, a conventional sonar system with an up-chirp signal did not yield reliable results because of its ambiguous property in simultaneous parameter estimation.
Humpback whale sonar
Authors: Mercado Eduardo , Frazer L. Neil , Herman Louis M.
Published: October 2005

During the winter months male humpback whales produce long complex sequences of sounds which have been described as song. Current hypotheses for the function of humpback whale song speculate that it serves primarily to provide other whales with information about the singer such as location and reproductive fitness. An alternative possibility, however, is that male humpback whales vocalize to obtain information about other whales through active acoustic interrogation of their environment. Specifically, it is proposed that the primary function of humpback whale song is as a long-range sonar used by males to locate other whales. The conclusions are based on (a) comparison of humpback signal types and patterns with those of other echolocating species; (b) application of the sonar equation to measured sound levels of humpback singers and target strengths of whales; and (c) humpback behaviors observed in association with singing. The complexity of humpback song in comparison to the vocalizations of bats and odontocetes is an adaptation to the long-range acoustical signal distortion caused by multipathing. Song phrases, in particular, are designed for echoic recognizability in the multipath environment.
On the physics of sound waves generated and detected by cetaceans and bats
Authors: Raichel Daniel R. , Raichel Dina K.
Published: October 2005

Raichel [‘‘Cetacean perception of the environment—A theoretical approach,’’ J. Acoust. Soc. Am. 92, 2423(A) (1992)] postulated that cetaceans possess the ability to assess their surroundings through evaluation of acoustic reflections by resolving the presence of higher frequencies that arise from the inherently nonlinear nature of the sound propagation of the pulses that they emit. Palakalet al. [‘‘An acoustic perception model for echolocation signals,’’ J. Acoust. Soc. Am. 99, 2558(A) (1996)] developed a neurological model to explain the formation of auditory images as the mechanism of echolocation in bats. Time lapses for the return of echoes constitute the basis for perception of target distance and structural information. The manner in which cetaceans and bats use sound to navigate, find nourishment, and communicate must be quite similar, particularly since higher frequencies provide the key to precision of echolocation and target compliances. Nonreciprocity of signals bounced back to sources supplies additional information on the presence of variations in density, compliances, particle sizes, etc., in the propagation medium. It is also noted that the contortions of the melon of a beluga whale (Delphinapterus leucas) approximates the optimal shape of a radome for emitting and receiving signals.
Ultrasonic contrast agents and harmonic imaging
Authors: Shung K. Kirk
Published: October 2005

Significant progress has been made in recent years in the development of effective ultrasonic contrast agents for inducing better image contrast of certain anatomic structures in the body for diagnostic purposes. An ideal ultrasonic contrast agent should have the following characteristics: (1) be nontoxic, (2) be capable of producing sufficient contrast via intravenous injection, and (3) have a long persistence time. Gaseous contrast agents such as Albunex■ (Molecular Biosystems), Echovist■ and Levovist■ (Schering), and EchoGen■ (Sonus) have been shown to satisfy a majority of these requirements. Albunex■ was approved in 1994 by the FDA for clinical use. The most intriguing application of these contrast agents is in harmonic pulse-echo and Doppler imaging since nonlinear resonance of microairbubbles would yield echoes at the harmonics of the incident frequency. If detection is made at one of these harmonics, ideally only the signals produced by the bubbles will be seen, allowing a means to discriminate against echoes produced by surrounding tissue structures. In this paper the physical and ultrasonic properties of these agents will be reviewed along with principles of harmonic imaging. Clinical applications of these agents including harmonic imaging and Doppler flow measurements will be discussed. [Work supported by NIH Grant No. HL28452.]
Noninvasive measurement of motion velocity of the heart wall and its applications
Authors: Kanai Hiroshi , Sato Michie , Chubachi Noriyoshi , Koiwa Yoshiro
Published: October 2005

For the noninvasive diagnosis of heart disease based on the acoustic characteristics of the heart muscle, it is necessary transcutaneously to measure small velocity signals, including components with an amplitude of less than 100 μm/s, and to measure them continuously for periods of more than several heartbeats in a wide frequency range up to 1 kHz. Such measurement, however, has not been realized by any ultrasonic diagnostic method to date. By introducing the constraint least-squares approach, this paper proposes a new method for accurately tracking the movement of the heart wall based on both the phase and magnitude of the demodulated signal to determine the instantaneous position of the object so that the velocity of the moving object can be accurately estimated. By this method, a small velocity of the heart wall with small amplitudes less than 100 μm/s on the motion resulting from a heartbeat with large amplitude of 10 mm can be successfully detected, with sufficient reproducibility in the frequency range up to several hundred Hertz, continuously for periods of about ten heartbeats. The resultant small-velocity signal is analyzed not only in the time domain but also in the frequency domain. The new method offers potential for research in acoustical diagnosis of heart disease.
Measurement and correction of ultrasonic wavefront distortion
Authors: Waag Robert C. , Liu Dong-Lai , Hinkelman Laura M. , Mast T. Douglas
Published: October 2005

Wavefront distortion produced by transmission through abdominal wall, breast, and chest wall has been measured in a two-dimensional aperture and the abdominal wall measurements have been compared to distortion simulated using sound speed and density determined from stained cross sections. The results show that wavefront distortion varies with tissue type, scattering contributes significantly to distortion, and arrival time and energy level fluctuations can be large compared to increments in current beamformers. Focus degradation and compensation has also been investigated by reconstructing the time history of a virtual point source without compensation, with time-shift compensation in the aperture, and with backpropagation followed by time-shift compensation. Backpropagation followed by time-shift compensation was found to be more effective than time-shift compensation in the aperture. A comparison of wavefront distortion and compensation in one- and two-dimensional apertures has shown that distortion is smoothed increasingly by one-dimensional apertures with larger elevation dimensions and that one-dimensional compensation becomes less effective than two-dimensional compensation for larger elevations. Pulse-echo studies using different f-number transmitters have shown that wavefront aberration is significantly underestimated with a broad incident beam and demonstrated that a sharply focused incident beam is necessary for good estimation of time shifts and for effective compensation.
Three-dimensional prostate imaging and tissue typing
Authors: Feleppa Ernest J. , Fair William R. , Silverman Ronald H.
Published: October 2005

Three-dimensional (3-D) depictions of ultrasonic scan data have been developed in our laboratories for visualizing tissue properties and structure in several medical applications including characterization of prostatic and ophthalmic tissues. Data for 3-D depictions are acquired as a set of parallel ultrasonic scans and are displayed as volume or surface renderings or as interactively dissectable blocks. Acquired data consist of digitized radio-frequency (rf) echo signals. Tissue-typing information is based on parameters derived from linear-regression analyses of normalized power spectra of the digitized rf echo-signal data. Tissue properties, such as scatterer size, are computed from spectral parameter values. Tissue typing is performed by comparing computed parameter values from an unknown tissue with database values associated with known tissue types. Images portraying spectral parameter values, scatterer properties, or most-likely tissue type have been developed. Three-dimensional presentations are generated from sets of scan-plane data using desktop computers or imaging workstations. Volumes can be examined in several ways, e.g., by dynamically presenting the entire 3-D volume as a tilting or a rotating transparent rendering. Three-dimensional images of the prostate gland facilitate visualization of cancerous regions warranting biopsy. [Research supported, in part, by the National Cancer Institute and the National Eye Institute.]
Measurements of the spatial distribution of local heat generation due to irradiation of focused ultrasound
Authors: Watanabe Yoshiaki , Hasegawa Hiroshi
Published: October 2005

Applying ultrasound to hyperthermia treatment, the temperature rise caused by irradiation of focused ultrasound is discussed. A piezoelectric concave-shaped transducer whose radius of aperture is 100 mm, radius of concativity is 25 mm, and resonant frequency is 1 MHz is used. Glycerin is introduced as the phantom because of its transparency. The heat-sensitive tape which consists of thermometric ink covered with a Teflon thin film of 100 μm in thickness is used. The tape is spread out on the phantom with an observation area 50 mm long and 8 mm wide. The tape indicates the temperature as the color differences. The spatial distribution of the local heat generation, especially surrounding the focal point, is observed as a function of irradiation time. The experiments are carried out in the same kind of transmission conditions. The theoretical analyses for both the spatial thermal distribution and the time profile of the temperature rise are estimated by using the heat equation. The observed results show good agreement with the calculated ones.
Technique for stroboscopic analysis of the tip motion of ultrasonic surgical devices
Authors: Harris Gerald R. , Malinauskas Richard A. , Carey Ronald F.
Published: October 2005

Ultrasonic instruments used in surgical applications (e.g., ophthalmology, neurosurgery, dentistry) have vibrating tips driven at frequencies from 20 to 60 kHz, and maximum peak-to-peak tip excursions ranging up to several hundred micrometers. To study the tip motion, a stroboscopic system has been developed consisting of a digitally generated delay that automatically steps through the excursion cycle, a commercial xenon flashlamp strobe, and optics that permit video display and recording. The digital delay uses two 8-bit, synchronous binary counters with asychronously loaded data inputs. These counters are configured so as to produce a pulse train for strobe triggering that has successive pulse periods that differ by one clock cycle. Of the two possible sources for image blur, the finite light pulse duration and strobe jitter, the former is more significant because light pulse durations of less than 1 μs are difficult to obtain with xenon flashlamps. Image magnifications of up 550× are possible with the technique, with a tip displacement resolution of approximately 5 μm. The technique has been used to visualize the tip motion of an ophthalmic phacoemulsifier operating at 28 kHz and having a maximum tip excursion of 100 μm.
A new approach to modeling a backed transducer by the finite element method
Authors: Assaad Jamal , Talbi Rachid , Boudy Pierre
Published: October 2005

Backed transducers are widely used in acoustics and ultrasonic imaging. The finite element method (FEM) has been employed to characterize these transducers. But generally, the backing has not been considered. In fact, to model backed transducers by the FEM, the main drawback is generally the large size of the numerical problem. The aim of this paper is to show how the backing mesh can be quite limited. As will be shown in this paper, this is possible by reducing the thickness of backing TB and by scaling up the tangent of the phase angle (tan δ) keeping the product TB tan δ constant. Experimental results concerning a lithium niobate transducer bar are compared to the numerical one obtained by the FEM. Moreover, it will be shown that when an additional layer is placed between the backing and the piezoelectric material, the transducer bandwidth decreases.
Excitation of shear waves inside of rubberlike material by focused ultrasound
Authors: Andreev Valery , Pishalnikov Yury , Rudenko Oleg , Sapozhnikov Oleg , Dmitriev Vladimir , Sarvazyan Armen
Published: October 2005

It is known that the difference in shear modulus for normal tissues and for pathological ones can reach two or three orders. This is the basis for the development of a very sensitive medical diagnostics method. Shear stresses inside of tissue can be excited by a focused ultrasound. The efficiency of this process is the main problem. The phenomenon of shear wave excitation by a focused acoustical beam has been studied experimentally and theoretically. In the experiment a shear wave has been excited in rubberlike material (transparent polymer) by powerful focused ultrasonic beam in a pulsed regime. The registration of the shear deformation has been performed by means of an optical beam, which was focused at a target in the thickness of polymer sample. Temporal profiles of a shear wave have been registered at different distances from the focal region. The measured value of shear wave velocity was in a good agreement with its theoretical prediction. A theoretical model of shear wave generation by a beam of a longitudinal wave has been developed. An analytical expression for the pulse response function was derived which allows one to study the spatial and temporal characteristics of the shear wave.