bluuebunny/crossref_metadata_2025 huggingface dataset:
Variable rate codec for speech and audio
Authors: Howitt Andrew Wilson
Published: October 2005

Most voice and audio codecs are optimized for fixed bandwidth streaming channels. There is a growing need for codecs which operate efficiently over variable bandwidth packetized channels, such as Internet telephony. A novel codec structure is proposed which is optimized for packetized channels. It allows dynamic trade-off between bandwidth, quality, and computational load. Block normalization is performed by segmenting the signal into short time epochs of similar amplitude, and renormalizing each epoch, which greatly decreases dynamic range requirements for subsequent coding. The degree of ‘‘intelligence’’ used to find these segment boundaries can be tailored to balance bandwidth against computational load. Channel squelch is performed by suppressing transmission of packets with low amplitude. In this way, silent epochs consume zero bandwidth. The threshold for suppression can be tailored to balance quality against bandwidth. Experiments were conducted to evaluate several versions of the codec, examining bandwidth, computation, and quality (as measured by DMOS testing). Results show good quality at bandwidths and computational loads appropriate for home computers with modem connections to the Internet.
Interpolating HRTF for auditory virtual reality
Authors: Nishino Takanori , Mase Sumie , Kajita Shoji , Takeda Kazuya , Itakura Fumitada
Published: October 2005

Two (linear and nonlinear) interpolation methods of the head-related transfer function (HRTF) are exploited in order to realize virtual auditory localization. In both methods, HRTFs of the left and right ears are represented by a delay time and a common impulse response, where delay time is determined so that the cross correlation of two HRTFs takes the maximum value. A three-layer neural network is trained for the nonlinear method, whereas basic linear interpolation is used for the linear method. Evaluation tests are performed by using HRTF prototypes, Web-published by the MIT Media Lab. The signal-to-deviation ratios (SDR) of the measured and interpolated HRTFs are calculated for objective evaluation of the methods. The SDR of the nonlinear method is much better, i.e., 50 to 70 dB, than that of the linear method, i.e., 5 to 30 dB. On the other hand, there is no significant difference in the subjective evaluation of localizing the earphone-presented sounds generated by the two interpolated HRTFs. Furthermore, the results of the above subjective tests are nearly identical to that of the measured HRTF.
A time-varying ARMAX speech analysis method based on the glottal source model
Authors: Funaki Keiichi , Miyanaga Yoshikazu , Tochinai Koji
Published: October 2005

Human speech production is usually modeled by an AR process with an impulse or white Gauss process input, such as in LPC analysis. But it is well known that a vocal tract feature provides an antiformant in addition to a formant frequency, and a voiced source of human speech contains a glottal source as well as noise characteristics. In order to represent speech production efficiently, a time-varying ARMAX (ARMA with eXogeneous input) model with a glottal source model is introduced. This model provides two MA processes, one for the white Gauss input and the other for the exogeneous input, which is generated by the glottal source model. A new speech analysis method is proposed that is based on the speech production model to extract speech characteristics accurately. In the proposed method, the Rosenberg–Klatt (RK) model [Klatt et al., J. Acoust. Soc. Am. 87, 820–857 (1990)] is adopted to generate a glottal wave. The glottal source and ARMAX parameters are estimated pitch synchronously and simultaneously, so as to optimize error criterion jointly by using an adaptive MIS method [Miyanaga et al., IEEE Trans. Acoust. Speech Signal Process. ASSP-34, 423–433] in ARMAX identification. Experiments have already been conducted using synthetic speech, which is generated by an ARMAX process with the RK model glottal source and a white Gauss input. The experimental result shows that the proposed method makes it possible to estimate accurate vocal tract and voice source characteristics (such as open quotient) from the speech signal.
A speech improver for hearing-impaired children using DP matching and SOM
Authors: Osogami Yukiko , Ishida Yoshihisa
Published: October 2005

This paper describes a new system, a speech improver, for hearing-impaired children. This system is composed of DP matching and SOM. The child’s voice is changed to a normal-hearing person’s voice by DP matching. However, the child’s voice feature is not changed by retaining its pitch information. In addition, the SOM compresses much input data for reference into a small pattern. The sound source (amplitude and pitch) and articulation of the child’s voice are managed separately. The amplitude comes from the LPF, and the pitch is obtained accurately by the authors’ method. The LPC power spectrum envelope which represents the articulation is obtained by applying the LPC and the DFT to the input child’s voice. Besides, the many spectra of the reference voice have been clustered by the SOM. These spectrum sequences of the input and the reference are the input of the DP matching. According to this output, the child’s voice spectrum is replaced by a reference spectrum. A synthesized voice is obtained by concatenating the replaced spectrum transformed into a time domain considering the pitch and the amplitude. The synthesized voice has been improved with the remaining characteristics of the child’s voice. Furthermore, this system corresponds to many childrens’ input voices, because it uses compressed patterns.
Seismoacoustic remote sensing of ‘‘edge waves’’ in the Arctic ice cover
Authors: Dudko Yuriy V. , Schmidt Henrik
Published: October 2005

As part of the ONR sea-ice mechanics initiative (SIMI) experiments in the spring of 1994, arrays of high-resolution seismic sensors were deployed in areas of high seismicity identified by real-time processing of acoustic emission events recorded by a wide, horizontal aperture hydrophone array. A major episode detected by the surveillance array was a new major lead opening up 2 km north of the ice camp. Two seismic arrays, each consisting of five three-component geophones in an 80-m aperture pentagon, were deployed 400 m apart on the edge of the lead. One of the methods employed for analysis of these data was the 2-D horizontal wave-number estimation of the recorded time series using plane wave beamforming. This procedure determined the propagation directions of arrivals of different wave types along with their dispersion characteristics. This analysis revealed a large number of events, corresponding to ‘‘edge waves’’ propagating in opposite directions along the lead. The analysis revealed that these waves behaved differently from the edge waves of bending-gravitational nature, predicted theoretically in the literature. Also, the broadband nature of these waves is inconsistent with floe resonances. To explain the nature of these waves, a simplified elastic model has been developed for the lowest-order modes of a floating, semi-infinite plate. The characteristics of the edge waves and the comparison with the simplified model are discussed. [Research supported by ONR.]
Spatial sampling issues for active-sonar performance predictions in shallow water
Authors: Leclere James H. , Del Balzo Donald R. , Bucca Paul J.
Published: October 2005

Predictions of active sonar performance at subkilohertz and a few kilohertz in shallow water are examined for a measured environment. The sound-speed profiles are derived from XBT and CTD data obtained during the acoustic characterization test (ACT) III in 100 m of water. Transmission loss, reverberation level and signal excess for a generic sonar system are calculated for several realistic geophysical bottom descriptions and water mass regions in the ACT III area. The sensitivity of acoustic predictions to spatial environmental variations are quantified and implications about space sampling strategies are discussed. The relative importance of changes in bottom properties to changes in water mass sound speeds are highlighted. [Work supported by NRL.]
A shallow-water experiment for estimating bottom geoacoustic properties at a site off Numazu
Authors: Ohkawa Keiichi , Tukimori Toshinao , Nakajima Hiroyoshi , Ohta Kazuhiko , Morishita Itaru , Ishiwata Tsuneo , Ozaki Shunji
Published: October 2005

An experiment to estimate bottom geoacoustic properties was conducted in the coastal area of Gulf Suruga off Numazu in August 1995. The measurements were made at a 70-m-depth site using a vertical line array of 12 receivers spaced at 5-m intervals. A cw source output at 55 Hz with 167 dB re: 1 μPa source level was towed at a constant depth over 3 km in horizontal range along the coast. Acoustic fields measured by a synthetic array at each channel were processed with a Hankel transform, whose output wave-number spectrum provided several peaks corresponding to mode eigenvalues. The position of each peak, however, varies slightly depending on the channel; this variation is considered to be caused by the range dependence of the waveguide and/or by mutual interaction of adjacent mode spectrum due to the finite aperture. Applying an inversion method to the observed mode eigenvalues, bottom geoacoustic parameters (sound speed, attenuation, and density) were estimated under several assumptions. Propagation loss calculated with use of the estimated parameters was found to be in good agreement with the observed one.
The behavior of mud pulse signals in drill pipes
Authors: Watanabe Tsuguhiko , Morita Naoki
Published: October 2005

The MWD (measuring while drilling) system, which transmits information such as temperature, pressure, direction, and inclination at the bottom of the hole to the surface of the earth while drilling, is used and is underdeveloped as a higher temperature version, but it was hoped that it would be more efficient in the oil fields and the geothermal fields as a supporting tool in drilling. The transmission from MWD is realized by the pulse interval modulation, which generates pulsed pressure waves and uses the interval of pressure waves to send physical information. This paper shows that our calculation results can accurately simulate the mud pulse in drill strings comparing them with experiments carried out in the laboratory and that, due to the loss of propagation depending upon well depths, the behavior of mud pulse signals apparently change. It is concluded that the simulation program is reliable for this system, and that the mud signal is useful from a 500- to 3000-m depth borehole.
Pressure effect on absorption coefficients in the deep-sea area
Authors: Tsuchiya Toshio , Hashimoto Kikuo , Umezawa Masaaki , Kikuchi Toshiaki , Hasegawa Akio
Published: October 2005

In order to design deep-sea acoustic devices, it is very important to estimate the sound absorption loss in the deep sea. In general, the Thorp equation [F. H. Fisher and V. P. Simmons, J. Acoust. Soc. Am. 62, 558–564 (1977)] is used in the design of deep-sea acoustic equipment for safety monitoring. However, it is known empirically that the measured absorption losses are less than the losses calculated by the Thorp equation [Tsuchiya et al., presented at the Meeting of the Marine Acoustics Society of Japan (1993), p. 77 (in Japanese)] in the deep-sea area. The sound absorption losses in the deep sea were measured using the deep submergence vehicle ‘‘SHINKAI 6500’’ of the Japan Marine Science and Technology Center (JAMSTEC). It is known that there is a discrepancy between the measured absorption loss in a water tank and that in the deep sea. The data are close to those measured in the laboratory by Fisher [F. H. Fisher, J. Acoust. Soc. Am. 38, 805–812 (1965)]. It appears that absorption loss decreases quadratically as a function of depth.
Acoustic current tomography of a coastal front in Haro Strait, British Columbia
Authors: Elisseeff Pierre , Schmidt Henrik , Johnson Mark , Chapman N. Ross , McDonald Mark M.
Published: October 2005

Various tomographic approaches are investigated for determining the spatial and temporal characteristics of the current field in the vicinity of a tidally forced coastal front near Stuart Island in Haro Strait, British Columbia (Canada). The front separates water masses with a current differential of 3 kn or more, corresponding to Mach numbers of 0.001 or higher. Three vertical receiving arrays were moored 2 to 4 km apart around the front. A variety of signals were transmitted across the water column: a 100-Hz-bandwidth linear FM sweep centered at 250 Hz, cw signals ranging from 100 to 350 Hz, and very wideband impulses with a strong spectral content from 150 to 850 Hz. Three current inversion schemes are compared: traditional travel time tomography, matched-field tomography, and linear full-field modal tomography. The latter is a novel algorithm based on cross-mode coupling coefficients appearing in the modal representation when an inaccurate or arbitrary mode set is used in place of the exact solution to the Sturm–Liouville problem. Its performance vis-a-vis bandwidth and signal-to-noise ratio is discussed. [Work supported by ONR.]
Second-order perturbations of peak-arrival times due to sound-speed disturbances
Authors: Athanassoulis G. A. , Skarsoulis E. K.
Published: October 2005

Ocean acoustic tomography has been commonly used in a linear framework, by assuming small perturbations of the ocean environment about a given background state. However, in the case of large sound-speed variations (e.g., seasonal changes) nonlinear dependencies of arrival times on the sound speed may become significant; such a case occurred in the THETIS-2 tomographic experiment conducted in 1994 in the western Mediterranean basin. Second-order arrival-time perturbations are studied here on a wave-theoretic basis, using the recently introduced notion of peak arrivals [G. A. Athanassoulis and E. K. Skarsoulis, J. Acoust. Soc. Am.97 , 3575–3588 (1995); Skarsoulis et al., J. Acoust. Soc. Am. 100 (August 1996)]. A second-order perturbation formula relating arrival-time with sound-speed perturbations is derived, containing background arrival times and also functional derivatives of the background field with respect to the sound speed. For the case of a range-independent environment the perturbation formula is further elaborated by exploiting normal-mode theory. Its performance is demonstrated using simulations motivated from the THETIS-2 environment. [Work partially supported by EU/MAST.]
Mathematical modeling of Stonely wave propagation
Authors: Assaoul Viktor N. , Gribin Serguei V.
Published: October 2005

Long distance propagation of a Stonely wave is caused by the concentration of the wave energy in the thin layer near the bottom. Such a property makes it possible to use the generation of a Stonely wave for transmission of information. The main applications can be concerned with registration of volcano eruptions, underwater explosions, and elaboration of new methods of long distance communications. The mathematical model calculations are analyzed and confirm the possibility of the long distance propagation and use of a Stonely wave in the applications mentioned above.
Sound transmission through structures—protecting occupants from exterior noise
Authors: Sharp Ben H.
Published: October 2005

In most aspects of our lives, people encapsulate themselves in enclosures of one kind or another to provide separation and protection from local harsh environments, i.e., temperature, weather, fire, air flow, air pressure, etc., and to provide privacy and protection from predators. This encapsulation also provides some degree of protection from noise—often more by accident than design, for structural noise reduction is not always at the top of the list of design priorities. In order to provide adequate protection from noise for people and sensitive equipment in enclosed spaces, it is necessary to work within the design constraints imposed by the harsh environments. In many cases, this means that a rudimentary understanding of sound transmission through structures is not sufficient to achieve the necessary protection, and more advanced techniques are required. This tutorial will provide an overview of the principles of sound transmission through materials, highlighting some of the more common misconceptions, and presenting the design of structures for special applications. Examples will be given of the techniques and designs used in the expanding market for the sound insulation of buildings exposed to aircraft noise.
Aspects of uncertainty in room acoustical computer simulation and auralization
Authors: Vorländer Michael , Behler Gottfried K.
Published: October 2005

Sound field simulations for parameter predictions and for auralization are affected by several factors influencing the quality of the simulation. These factors can be combined into groups of (a) simulation input data (absorption, diffusion, directivities, etc.), (b) algorithm details (systematic and stochastic errors), (c) signal processing (filtering, HRTFs, phase generation), and (d) auralization setup (convolution hardware, sound field reproduction). The magnitude of the errors can be checked by experiments, by listening tests, and by intercomparisons. Particularly, intercomparisons gave interesting indications of error sources in the algorithms caused by simplifications and compromises between complexity and processing time. After a brief description of the software developed, the recent work on the relevant factors of auralization and the necessary efforts for obtaining reasonable results are discussed.
Visualization and auralization for architectural acoustic simulation
Authors: Tsuru Hideo , Tadahira Yoshio , Tsutsumi Masatoshi
Published: October 2005

Numerical simulation of the acoustic field for a large concert hall is normally executed by geometrical acoustics. Although it is a classical method, it needs considerable calculations for practical applications for a large hall. Therefore, some algorithmic technique is needed. As the simulated result contains three-dimensional information, its visualization is useful for intuitive understanding of the field. An auralization of the simulated result is also presented. Because the wave nature of the field should be considered for long wavelength sound, a wave acoustical simulation technique is proposed, which is based on a boundary-element method. A comparison of results from geometrical acoustics and wave acoustics is also presented.
Concert performance in virtual reality
Authors: Takala Tapio , Hanninen Rami , Savioja Lauri , Valimaki Vesa , Huopaniemi Jyri , Huotilainen Tommi , Karjalainen Matti
Published: October 2005

An integrated computer graphics and audio signal processing system is developed for producing real-time audiovisual performances, such as a virtual concert. Animated musician models play MIDI-coded music, with hands and fingers synchronized to each note by kinematic calculations. Instrument sounds are synthesized by physical modeling techniques. Acoustic response of the concert hall is calculated based on its geometric model and material information. Ray tracing and image source methods are used for early reflections, whereas a recursive filter structure, consisting of comb and allpass filters, models the later diffuse reverberation. For three-dimensional sensation of the environment, the direct sound is auralized with a FIR approximation of the listener’s head-related transfer function (HRTF), and the image sources are processed with the interaural amplitude and time differences (IAD and ITD). The system implementation is distributed over a high-speed network using workstations for the visual and interactive parts and a dedicated digital signal processor for sound synthesis and HRTF convolution. The listener may freely move in the virtual concert hall using a mouse controller. Methods for conducting the virtual orchestra with a tracker baton are under development. [Work supported by the Academy of Finland.]
Auralization on a laptop PC
Authors: Michalson William R.
Published: October 2005

There are many well-known techniques for performing auralization. Most involve real-time convolution using extremely powerful, custom-built signal processing hardware. These systems tend to be complicated and expensive, but they are necessary when the goal is to alter room or hall acoustics for a professional performance or recording. At WPI our goal was to develop a much simpler auralization system that could be used for educational purposes. The approach taken was to implement Gardner’s algorithm for performing efficient convolution on a Windows-based personal computer. The resultant system allows performing reasonably fast auralization on arbitrary length source and room impulse response files. Students can then play back these files to hear the differences between previously created room impulse responses.
Effectiveness of interaural delays alone as cues during dynamic localization of virtual sources
Authors: Wenzel Elizabeth M.
Published: October 2005

The contribution of interaural time differences (ITDs) to the localization of virtual sound sources with and without head motion was examined. Listeners estimated the apparent azimuth, elevation, and distance of virtual sources presented over headphones. Stimuli (3-s, white noise) were synthesized from minimum-phase representations of nonindividualized head-related transfer functions (HRTFs); binaural magnitude spectra were derived from the minimum phase estimates and ITDs were represented as a pure delay. During dynamic conditions, listeners were encouraged to move their heads; head position was tracked and stimuli were synthesized in real time using a Convolvotron to simulate a stationary external sound source. Two synthesis conditions were tested: (1) both interaural level differences (ILDs) and ITDs correctly correlated with source location and head motion and (2) ITDs correct, no ILDs (flat magnitude spectrum). Head movements reduced azimuth confusions primarily when interaural cues were correctly correlated, although a smaller effect was also seen for ITDs alone. Externalization was generally poor for ITD-only conditions and was enhanced by head motion only for normal HRTFs. Overall, the data suggest that, while ITDs alone can provide a significant cue for azimuth, the errors most commonly associated with virtual sources are reduced by location-dependent magnitude cues.
Auralization of localization cues
Authors: Valiani Waqar-Un-Nissa , Hodgson Murray , Pichora-Fuller M. Kathleen , Schneider Bruce
Published: October 2005

Auralization has the potential for assessing the difficulties faced by listeners in nonideal conditions. Thus simulated environments were created using a commercial auralization system from Tucker–Davis Technologies. A small reverberant test room was simulated in order to present test stimuli to subjects binaurally. This simulation took into account direct sound, the six first-order reflections, an approximate reverberant tail to account for higher-order reflections, the reflective properties of the room’s surfaces, the head-related transfer functions, and the source–receiver position in the room. To validate the simulation, the localization perception of listeners in the real and virtual environments were compared. In the real room, localization was accurate with feedback; without feedback approximately 10% of front–back confusions occurred. Localization performance in the virtual condition as compared to the real condition was found to be comparable. [Work supported by NSERC.]
Acousto-fluidic sound augmentation for Orthodox Jewish worship spaces
Authors: Drzewiecki Tadeusz M. , Poindexter Joseph C.
Published: October 2005

An acousto-fluidic sound augmentation system has been developed which provides adequate sound coverage in worship spaces accommodating as many as 1600 persons. Because of the unique religious restrictions of Orthodox Judaism, use of electricity and sound reproduction per se are prohibited while sound augmentation is permissible as long as the original sound is preserved and no apparent sound amplification occurs. A kosher sound system has been built and tested with essentially 0-dB sound-level gain but about 50 dB of power gain when operating with a 10-psi air source. The system frequency response is flat from 700–3500 Hz, and cuts off at 200 and 6000 Hz, respectively. A single-channel output comprises two 180° out-of-phase ElectroVoice HB640 horns. The monaural sound quality is good enough for recognition of the speaker’s voice with good reproduction of sufficient overtones to render singing pleasant. Sounds can be transmitted up to 25 m through 5-cm-diam PVC pipes thereby allowing speakers to be placed far enough away from the inputs to ensure good aural reception at the furthest reaches of worship spaces. The inherent acoustic delay obviates the need for the introduction of artificial delays and consequently results in very natural sound propagation and rendition.
Geographic and temporal variation in songs of humpback whales
Authors: Helweg David A.
Published: October 2005

Humpback whales (Megaptera novaeangliae) migrate annually between high-latitude summer feeding waters and low-latitude winter mating waters. During migration and in winter waters, adult [male] humpbacks produce long complex songs. Songs gradually change during each singing season, and singers incorporate changes as they occur. Classification of song units using neural networks and cepstral cross correlation reveals that variability in song characteristics within region is lower than variability between regions. These regional differences in song characteristics can be considered to be dialects that are maintained through cultural transmission of regional variants. Thus differences in songs from different regions may be an index of reproductive isolation. Cladistic patterns of geographic and temporal variation in songs support a model of limited migratory exchange among widely separate wintering regions. [Work supported by UARC, SPREP, WDCS, PDCT.]
A comparison of the vocal repertoires of beluga whale populations in Bristol Bay and the Beaufort Sea, Alaska
Authors: Angiel Nicole M. , DeMaster Douglas P. , VanBlaricom Glenn R.
Published: October 2005

Little is known about the acoustic behavior of Alaskan beluga whales, as their vocalizations have not been fully cataloged. Alaskan belugas summering in different regions are assumed to constitute distinct populations, but uncertainty remains about where to draw stock boundaries. Geographic variation in bioacoustics refers to dissimilarities in vocalizations between isolated, noninterbreeding populations of the same species. It occurs in many avian species and several mammalian species, and has been suggested for beluga whales in Russian waters. Geographic variation represents local adaptation and may lead to the development of new species. It is therefore important in conservation biology and management and should be considered in stock designation. Beluga whales from Bristol Bay and the Beaufort Sea are believed to constitute distinct stocks, but the extent to which they interbreed is unknown. A preliminary analysis of genetic distance between these putative stocks indicate genetic exchange is rare. This study characterizes and compares the vocal repertoires of these two populations. The data contribute to our understanding of beluga acoustic behavior and may contribute to the development of a noninvasive tool for elucidating stock structure in beluga whales.
Graded structure of false killer whale (Pseudorca crassidens) phonations: Implications for production models
Authors: Murray Scott O. , Mercado Eduardo , Roitblat Herbert L.
Published: October 2005

Odontocete phonations have traditionally been classified into three mutually exclusive categories: (1) click trains, (2) burst-pulse sounds, and (3) whistles. An analysis of phonations from two false killer whales revealed that these categories are not actually distinct and that gradations exist between them. In a sample of 152 whistles, 80% had a pulsed component with a pulse train occurring before, during, and/or after whistle production. Many whistles could be seen to fade into and out of pulsed signals that aurally and spectrographically could appear as click trains or burst-pulse signals. These associated pulsed signals matched the signal characteristics of the whistles, including peak frequencies. The mechanism that produces whistles also seems to produce pulsed signals. Based on waveform and spectral analysis, at least three states in the gradation from whistle to click train can be identified: (1) amplitude modulations of the whistle, (2) a secondary spike in the whistle waveform, with the second harmonic appearing as the fundamentals, and (3) rapidly pulsing oscillations appearing as harmonic bands. The observation of independent whistles and clicks suggests that there are at least two sound-producing mechanisms. The occurrence of graded signals is significant when considering the function and information content of animal signals.
Burst-pulse sounds of a neonate bottlenosed dolphin
Authors: Killebrew Deirdre A. , Mercado Eduardo , Pack Adam A. , Herman Louis M.
Published: October 2005

Vocalizations produced by a neonate male bottlenosed dolphin during the first 5 days after birth were compared to the vocalizations of two adult female bottlenosed dolphins housed in the same enclosure. Audio and video recordings were made of the focal mother and her calf from birth. Calf vocalizations were identified as sounds that occurred concurrently with the emission of bubble streams by the calf. Adult vocalizations were recorded prior to, during, and after the birth of the calf. Initial calf vocalizations were of a single sound type varying in duration from 0.35 to 1.4 s. The sounds produced by the calf were broadband signals with spectral energy from approximately 0.5 to 9 kHz and peak energy levels between 1.2 and 1.6 kHz. Spectrographic and aural analyses of sounds made by the calf and adults revealed that calf vocalizations were more similar to the burst-pulse sounds of both adults than to any other vocalizations of either dolphin. Evolution of the calf’s sounds toward narrow-band frequency-modulated whistles was evident in later recordings. These results contrast with previous reports that bottlenosed dolphins produce whistles from birth and elucidate relationships between the production of whistles and burst-pulse sounds and their ontogeny.
Open-water echolocation of bottom objects by dolphins (Tursiops truncatus)
Authors: Sigurdson John E.
Published: October 2005

The interpulse-intervals, 3-D-head-attitudes, azimuths, and pulse waveforms of two Atlantic bottlenose dolphins were recorded while they searched successive circular bottom areas of 80-yd radii in the open ocean to echolocate bottom objects at depths of 40–50 ft. The animals remained near the center of the area while searching the bottom for 8-in., half-tri-planes on steel plates with both the location of animals and objects determined by a high-accuracy GPS. The animals were rewarded for correctly reporting the presence or absence of objects that were placed at a random 50% of the stations and, where present, randomly distributed over station area. The derived scan patterns and pulse spectra provide a systematic description of open-ocean echolocation of bottom objects. As in previous work with water-column objects in a single field, these animals adapted their spatial distributions of ensonification to their recent experience with detected objects (i.e., the search area). Head orientation and interpulse intervals were correlated with object location on object-present trials while analysis of the pulses-on-object as a function of distance, echo-to-pulse delays, and consistency of the pulse spectra showed important differences between the open-water test scenario and the more traditional tests with animal and targets in static positions.
Dolphins can immediately recognize complex shapes across the senses of echolocation and vision
Authors: Pack Adam A. , Herman Louis M.
Published: October 2005

Pack and Herman (1995) revealed that in ‘‘cross-modal’’ matching tests, a dolphin could spontaneously recognize the shape of an object through one sense (either echolocation or vision) that it had earlier interrogated through the alternate sense [A. A. Pack and L. M. Herman, J. Acoust. Soc. Am. 98, 722–733 (1995)]. Objects exposed to the echolocation sense were presented underwater in an anechoic box fronted by opaque Plexiglas. Objects exposed to the visual sense were presented in air ‘‘live’’ or on a television monitor. Eight unique pairs of 16 shapes were tested. Recognition was immediate across these pairs both going from echolocation to vision (E–V matching) and from vision to echolocation (V–E matching)—no learning of shape was required. The present study re-paired subsets of these shapes, thereby contrasting many more features. Twenty-five completely new pairings were tested. Performance on the first two unique trials with each pair provided the measure of immediacy of recognition. The dolphin chose correctly on 49 of 50 of these trials under E–V matching and on 44 of 50 during V–E matching. Together, the results of both studies strongly support the hypothesis that the dolphin’s echoic perceptual system can construct rich spatial representations of objects.
Echolocation rates of harbor porpoises, a bottlenose dolphin, and a baiji
Authors: Akamatsu Tomonari , Hatakeyama Yoshimi , Wang Ding
Published: October 2005

The echolocation events of free-ranging harbor porpoises, a bottlenose dolphin, and a baiji were observed by a compact acoustic signal detector (click light) and a hydrophone (B&K8103). The click light harnessed on a dolphin with a hydrophone above the melon of the dolphin lit at every detection of echolocation events. It was assumed that a series of pulses corresponded to an echolocation event. The hydrophone beside a tank could also receive echolocation events from the dolphins. Echolocation events from two harbor porpoises kept in a tank and in a net enclosure were observed by the click light. The bottlenose dolphin with the click light was kept in a circular pool. The echolocation events from the baiji were observed by a hydrophone beside a pool of the Institute of Hydrobiology in China. The echolocation events per minute (echolocation rate) ranged from 0 to 25. The echolocation rate changed frequently for all three species. The dolphins could be swimming without echolocating for a few minutes. Feeding induced higher echolocation rates. Enclosure types and human disturbances during experiments also affected the echolocation rates. Visual deprivation for the bottlenose dolphin or a dark condition for the harbor porpoises significantly increased the echolocation rates.
Low-frequency hearing in three species of odontocetes
Authors: Nachtigall Paul E. , Au Whitlow W. L. , Pawloski Jeffrey
Published: October 2005

The low-frequency underwater hearing thresholds for pure-tone signals between 75 and 1600 Hz for an Atlantic bottlenose dolphin, a false killer whale, and a Risso’s dolphin were determined using behavioral measures. All thresholds were obtained behaviorally by training the animals to station in a hoop and press a response lever when sounds were presented and to wait in the stationing position if no sound was heard. Data were collected using a staircase procedure with signals presented in 1-dB steps. Thresholds were then determined when the means for two consecutive ten reversal sessions differed by no more than 3 dB. In comparison to very sensitive hearing capabilities for these odontocete species at high frequencies, all animals showed relatively poor hearing for these lower frequencies. Most thresholds exceeded 125 dB re: 1 Pa.
Effects of scaled ATOC playbacks on the behavior of humpback whales in Hawaii
Authors: Frankel Adam S.
Published: October 2005

A shore-based team observed humpback whale behavior and movements before, during, and after a playback of the ATOC m-sequence. Eighty-four trials were conducted with both ATOC and no-sound control conditions. Shore observers did not know which sound condition was used. Playbacks originated from a projector suspended beneath a moored boat. The source level was 172 dB re: 1 μPa (60- to 90-Hz band). A second drifting vessel measured received levels and ambient noise. Received levels were measured between 105 and 130 dB. No overt responses were noted during the experiment. Movement and behavioral variables were examined for changes due to playback. Comparison of whale tracks between control and experimental conditions showed no difference in distribution. Preliminary analysis of the data found no changes in the movement variables and a slight change in respiratory behavior. Whales appear to have longer surface intervals during playback then during control trials. The magnitude of this effect on humpbacks appears to be comparable to effect of small vessels.
Removal of environmental effects from whale calls using coherent beamforming methods
Authors: Thode Aaron M. , D’Spain Gerald L. , Kuperman W. A. , Hodgkiss William S.
Published: October 2005

Coherent beamforming with point constraints (MPC) and matched-field processing (MFP) techniques are used to remove multipath reflections from whale vocalizations recorded on a 64-element 120-m vertical aperture array suspended from R/P FLIP. From a rough estimate of the whales’s location, the beamformer response required to cancel the surface and bottom reflections is constructed. The CMPC algorithm then derives the appropriate array element weightings. The beamformed output at each frequency is summed and inverse-transformed to reconstruct the original whale call. MFP is an alternate method for removing reflections from sounds generated within well-defined acoustic environments. MFP yields an estimate for the range, azimuth, and depth of a calling whale, which in turn allows subsequent calculation of the amplitude and phase shifts experienced by the call’s frequency components during propagation. The transfer function of the channel is thereby constructed and removed from the received call spectrum, producing another estimate of the whale source signal. The recovered signal spectrum are compared to spectral estimates obtained by incoherent averaging across phones and single-phone cepstral analysis to examine their utility for situations where coherent multiphone data are unavailable. [Work supported by ONR.]
Occurrence of blue and fin whales calls in the north Pacific as monitored by U.S. Navy SOSUS arrays
Authors: Stafford Kathleen M. , Fox Christopher G.
Published: October 2005

NOAA’s Pacific Marine Environmental Laboratory (PMEL) has been monitoring U.S. Navy SOund SUrveillance System (SOSUS) data from the northeast Pacific since 1991. Beginning in May 1995, additional hydrophone arrays were made available to PMEL for the study of underwater earthquakes, volcanoes, and whale acoustics. The addition of these data has made it possible for monitoring of low-frequency (60 Hz) whale calls over large areas of the north Pacific. Thirteen arrays in the north Pacific were grouped into five subregions: nearshore NE Pacific, offshore NE Pacific, central Aleutians, western Aleutians, and northwestern Pacific. SOSUS data were examined for the presence or absence of four different call types, two each from presumed blue (Balaenoptera musculus) and fin (B. Physalus) whales. The blue whale call types included the A–B pair [Thompson et al., Mar. Mamm. Sci. 12, 288–292 (1996)] and the two-part call described by Thompson and Friedl [Cetology 45, 1–19 (1982)]. Fin whale calls were divided into two groups based on the pattern and frequency content of the call series. Seasonal and geographic variation were found for all four call types.
Variability of acoustic transmissions in the Strait of Gibraltar
Authors: Cornuelle Bruce D. , Worcester Peter F. , Send Uwe
Published: October 2005

The Strait of Gibraltar Acoustic Monitoring Experiment was conducted during April–May 1996 to determine the feasibility of using acoustic methods to monitor the transport through the Strait of Gibraltar. Three different approaches to monitoring the flow were explored: (i) Traditional reciprocal ray differential travel times were obtained from three 2-kHz transceivers. (ii) A horizontal array of two 2-kHz receivers was installed on one of the acoustic paths across the Strait to test the feasibility of using horizontal arrival angles (phase differences) due to ray bending by the currents to measure the flow. (iii) A low-frequency (250-Hz) source transmitted to a 350-m vertical receiving array on the opposite side of the Strait to begin to examine the feasibility of using modal analyses, matched-field tomography, and full-field inversion techniques to obtain data on the temperature and current fields. Our initial efforts are aimed at examining the stability of ray and mode propagation and quantifying the accuracy of existing acoustic propagation codes in the complex oceanographic environment that exists in the Strait. Extensive independent measurements of the temperature, salinity, and velocity fields along and perpendicular to the acoustic paths were obtained. [Work supported by ONR.]
Coastal front tomography in the Haro Strait experiment: High resolution ray-based techniques
Authors: Deffenbaugh Max , Schmidt Henrik , Johnson Mark
Published: October 2005

The coastal environment presents some unique challenges for ray-based acoustic tomography. The need to resolve travel time effects of environmental changes over smaller distance scales pushes the experiment designer toward higher frequencies, but higher frequency signals are more susceptible to unmodeled features of the environment like surface and bottom roughness and micro-structure within the water column. At Haro Strait, it was found that these unmodeled features of the environment had a greater overall impact on the received acoustic signal than did the features of interest. Two techniques proved useful in improving the environmental estimates under these conditions. The first technique was a matched filtering of the received signal which emphasized those parts of the signal most sensitive to the environmental features of interest and least sensitive to unmodeled features of the environment. The second technique was adaptive repositioning of one of the tomography sources, made possible by mounting the source on an AUV. Tomographic resolution is dependent on the source/receiver geometry, and by repositioning a source, resolution can be concentrated at emerging features of interest. The improved resolution offered by these techniques is shown in the data from Haro Strait. [Work supported by ONR.]
Horizontal refraction tomography with mode interaction
Authors: Voronovich A. G. , Shang E. C.
Published: October 2005

Measurements of horizontal refraction angles associated with horizontal refraction of different acoustic modes can be used for inferring 3-D ocean inner structure [A. G. Voronovich and E. C. Shang, J. Acoust. Soc. Am. 98, 2708–2716 (1995)]. Numerical simulations demonstrated that the corresponding inversion scheme works very well for adiabatic propagation. It was also shown that the nonadiabatic case can be incorporated into the inversion scheme when mode interactions can be approximately accounted for by modifying local values of propagation constants of modes. In the present investigation, mode interaction is taken into account in a much more realistic ‘‘N×2-D’’ approximation (only relatively weak azimuth coupling is neglected). A new exact algorithm was used for the calculation of mode interactions in the plane of propagation. Numerical simulations showed that in many cases, the effect of mode interactions on horizontal refraction is rather weak and can be taken into account by rapidly converging iterative procedure. The results of tomography reconstruction of mesoscale inhomogeneities typical for the Pacific are demonstrated. [Work supported by ONR.]
Observations, characterizations, and acoustic effects of nonlinear internal waves on the Mid-Atlantic Bight continental shelf
Authors: Chiu Ching-Sang , Lynch James F. , Orr Marshall , Taube Donald W. , Ng Seng L.
Published: October 2005

During the summer of 1995, a multi-institutional field study called Shallow Water Acoustics in a Random Medium (SWARM) was conducted in the Mid-Atlantic Bight continental shelf region off the coast of New Jersey. Environmental and acoustic sensors were deployed as part of SWARM to measure and characterize the nonlinear internal waves and their impact on the spatial and temporal coherence of the acoustic transmissions. As part of the environmental monitoring network, two bottom-moored, upward-looking acoustic Doppler current profilers (ADCPs) were deployed. An oceanographic, modal, time-series analysis of the ADCP data reveals that: large-amplitude, nonlinear, internal wave packets were generated at multiple sites near the shelfbreak; the generation mechanism was consistent with the lee-wave hypothesis of generation; the propagation characteristics were in good agreement with nonlinear soliton theory; and the power spectral density was spatially varying and changed markedly during the passage of these nonlinear waves. Based on these observations, a canonical model of the induced sound-speed perturbations was developed. Using a coupled normal-mode propagation model, the temporal and vertical structures of the sound field were subsequently calculated for comparison to data obtained by a vertical line array. [Work supported by ONR.]
Internal tide impact measured by acoustic tomography experiment
Authors: Stephan Yann , Demoulin Xavier , Jesus Sergio , Ferreira Coelho Emanuel , Porter Michael B.
Published: October 2005

The INTIMATE (internal tide impact measured by acoustic tomography experiment) project is devoted to the study of internal tides by use of acoustic tomography schemes. The first exploratory experiment was carried out in June 1996 on the continental shelf off the coast of Portugal using a towed broadband acoustic source (500–800 Hz) and a four-hydrophone vertical array. Acoustic data were collected for 5 days, including legs where the source ship was moving and legs with the ship on station. Intensive environmental surveys (XBT, CDT, bottom and hull-mounted ADCP, thermistor chain, bathymetry, geoacoustic characteristics of the sediments) were also conducted. The purpose of the presentation is to give the preliminary results of acoustic data processing and to evaluate the impact of internal tides on the acoustic propagation in a shallow water environment. Future works will deal with inversions in terms of sound speed and geoacoustic parameter estimation. [Work supported by SHOM-IH-UAL. The hydrophones array was provided by the SACLANT Undersea Research Center, La Spezia, Italy.]
Fast normal-mode approximation of tomographic arrival patterns
Authors: Skarsoulis E. K.
Published: October 2005

The wave-theoretic calculation of arrival patterns for the needs of ocean acoustic tomography is computationally expensive due to the large number of computation frequencies necessary for properly synthesizing a broadband signal in the time domain. A scheme for approximate fast normal-mode calculations of broadband acoustic signals in the time domain is proposed, based on a second-order Taylor expansion of eigenvalues and eigenfunctions with respect to frequency. For the case of a Gaussian impulse source, a closed-form expression is obtained for the pressure in the time domain. Using perturbation theory, analytical expressions are derived for the first and second frequency derivatives of eigenvalues and eigenfunctions. The proposed approximation significantly accelerates arrival-pattern calculations, since the eigenvalues, eigenfunctions, and their derivatives need to be calculated at a single frequency, the central frequency of the tomographic source. Furthermore, it offers a satisfactory degree of accuracy for the lower- and intermediate-order modes. This is due to the fact that essential wave-theoretic mechanisms such as dispersion and frequency dependence of mode amplitudes are contained in the representation up to a sufficient order. Numerical results demonstrate the efficiency of the method. [Work partially supported by EU/MAST.]