bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthetic aperture analysis using SEABEAM2000
Authors: Asada Akira , Ueki Toshiaki
Published: October 2005

For the purpose of higher resolution measurement of seabed topography, hydrophone signals of SEABEAM2000 were analyzed by using the synthetic aperture technique. The investigative line was 5 km in length at a depth of water of 500–1000 m in the Sagami Bay. Sailing was careful and slow in order to suppress the deflection from the planned line. The signals of 42 hydrophones, were recorded for 1 h by a 48-kHz sampling frequency. In order to measure a deflection from the planned line, a roll, a pitch and heading angle, and a kinematic GPS position were also recorded simultaneously. The reference orbit axis of the transmit array was obtained. In order to make multiple receive beamforming with no fluctuation on the reference orbit axis, each time-sampled hydrophone signal was corrected by time-shifting at each designed beam angle. This correction cancels the sum of deviation of the transmit array at transmission and the deviation of the hydrophone at receiving on each receive beam axis from the reference orbit axis. Finally, a synthetic aperture beamforming was put into practice by using 3- and 5-ping receive beams with no fluctuation on the reference orbit axis. As a result, the resolution of synthetic aperture beams became much higher.
Interpretation of a backscattering image for the prospecting of Co-rich Manganese Crust
Authors: Kodama Takayoshi , Maeda Kohei
Published: October 2005

The Metal Mining Agency of Japan (MMAJ) had started in operation a multibeam echosounder (HYDROSWEEP) on R/V HAKUREIMARU No. 2 in 1991. The Backscatter Imaging Program was developed in 1992 and started in operation in the next year. The theoretical method program by de Moustier and Alexandrou (1990) or statistical method program for correcting the refractive intensity of each beams are prepared. Ordinary, statistical methods are used to correct whatever has its basis in the mean reflective intensity of each incidence angle. The information derived in the backscatter image is highly significant for MMAJ prospecting the seafloor minerals. The Backscatter Image of Guyot, which exists in the central Pacific, shows the fossil reef structure such as the fringing reef, the inner reef, the sinkhole, and the features of basaltic structure, such as the dome-shaped summit and pinnacles. An abundance of Co-rich manganese crust between seamount tops and upper slopes are related to the presence of outcrops and nodules. Distribution of outcrops estimated from the backscatter image is coordinated to the data of sub-bottom profiling and others. The potential resources of Co-rich manganese crust using the area of outcrops measured with images and expected mean thicknesses of the crust can be estimated by collected samples.
Free vibration of a partially liquid-filled and partially submerged, clamped-free circular cylindrical shell
Authors: Chiba M.
Published: October 2005

A theoretical analysis and experimental study are presented on the free-vibration characteristics of a thin cantilever cylindrical shell partially submerged in a liquid. Emphasis is placed on the influence of the liquids inside and outside the shell, and on the free vibrations of the shell. In the analysis, the thin elastic shell is assumed to be submerged in a rigid cylindrical container with finite diameter. Coupled bulging-type natural frequencies are calculated for different values of the thickness ratio, aspect ratio, and liquid height. The effect of liquid heights both outside and inside the shell on the bulging-type natural frequency are clarified. The results are summarized in the form of engineering design data from which one can easily predict the natural frequency of a given tank containing a liquid and then partially submerged in a liquid. To confirm the accuracy of the theoretical analysis, an experimental study was conducted on a test cylinder made of polyester film. Excellent agreement between theoretical and experimental results was obtained.
Fundamental frequency estimation of speech signals using a nonlinear observer
Authors: Yoshihama Taro , Doi Asako , Ishida Yoshihisa
Published: October 2005

This paper describes a new method of estimating the fundamental frequency of speech signals using an adaptive Fourier analysis (AFA) algorithm based on the presumption of signal parameters using a nonlinear observer. The recursive presumption of signal parameters such as fundamental frequency can be effectively implemented by using the proposed AFA algorithm. Nonlinear observers can be used to measure nonlinear parameters which are included in observed signals. Recursive estimation procedures make it possible to follow the slow changes of signal parameters to be measured. In real-time signal analysis, the recursive algorithm is preferred to the conventional Fourier transformation because of this property. The AFA algorithm, which is based on the recursive discrete Fourier transform (RDFT), is a recursive algorithm for the simultaneous estimation of the Fourier coefficients and instantaneous fundamental frequency of speech signals. This AFA algorithm is applied to speech signals with an arbitrary length of the transform window. Further efforts are required for better convergence speed of the proposed algorithm, but this method is mostly capable of adapting and tracking nonlinear signals such as speech sound.
Feature extraction for a neural network classifier
Authors: Wellman Mark , Srour Nassy
Published: October 2005

Unattended ground sensor (UGS) networks are intended to detect and localize the presence of strategic relocatable targets in the theater of operation over several kilometers. Passive acoustic sensors, an integral part of UGS, have achieved a high level of maturity and will allow acoustic target classification for tracked and wheeled vehicles. Of primary importance in the classification problem is the selection of a robust feature extraction technique, tolerant of both the environment and the nonstationary nature of the acoustic signatures. Several feature extraction techniques were used with experimental acoustic data collected from a small baseline, circular array. Results will be presented of the classification for acoustic features using a backpropagation neural network with simple power spectrum, harmonic line association [J. A. Robertson, IIT Research Institute, in-house report], principal components [J. Mao and A. K. Jain, IEEE Trans. Neural Networks 6 (2) (1995)], and wavelet packet [K. Etemad and R. Chellappa, Proc. First Intl. Conf. on Image Processing (November 1994)] feature extraction techniques.
On the use of the zero-crossing analysis for multi-channel signal processing
Authors: Sugihara Takaaki , Kajita Shoji , Takeda Kazuya , Itakura Fumitada
Published: October 2005

Since time precision in finding delays between channels is one of the most important issues in estimating direction of arrival (DOA) from multichannel signals, a zero-crossing analysis is proposed as a fine and robust time-domain preprocessing for the DOA finding. As for the preliminary evaluation of noise robustness using zero-crossing information, how the zero-crossing points are affected is investigated, i.e., how far the zero-crossing points move from the original points, under the presence of noise. For test speech, a 48-kHz sampling of a male voice (upsampled from an 8-kHz signal) is used after an adding machine generated white noise so that the SNR of the signal becomes 0 to 20 dB. The robustness of the zero-crossing analysis can be concluded from the summarized results: (1) the mean value of the distance is less than 100 μs throughout the SNR; and (2) the standard deviation of the distribution becomes large as the SNR decreases; the standard deviation is less than 0.125 even under the condition of 0 dB SNR.
Source identification using nonlinear signal processing
Authors: Quazi Azizul H.
Published: October 2005

Traditional techniques of signal processing in both the time domain and frequency domain are often not sufficient enough to characterize the complex dynamics of underwater sources that generated, radiate, and/or reflect sonar signals. The purpose of this paper is to analyze simulated signals by means of a nonlinear technique (based on mutual information), which is a completely new method that represents a revolutionary advance. Mutual information is a measure of the amount of information that one random variable contains about another random variable. It is also a reduction of uncertainty of one random variable, which is due to the knowledge of the other. Here the results of simulated sonar signal processing are presented based on mutual information and which is then compared to the traditional correlation technique. The results indicate that the mutual information is a more powerful tool compared to the correlation technique, and the results based on mutual information provide clues leading to source identification.
Broad bandwidth underwater transducer
Authors: Barger James E.
Published: October 2005

A new underwater transducer design technique is described that provides for ultrabroad-bandwidth directive arrays that are lightweight and thin (for easy towing). An example of this new technique is a planar array that is 1 m high, 0.75 m wide, and 0.15 m thick. This array has greater than 60% radiation efficiency throughout the frequency band extending from 400 Hz to 4 kHz, and a nominal power output within this band of 10 kW. The array is neutrally buoyant, and uses Navy type-III PZT actuators. The broadband goal is met by designing the transducers in such a way that their own stiffness reactances are mostly canceled by their masslike radiation reactances over the entire operating band. This feat is accomplished both by properly adjusting the ratio of actuator cross-sectional area to radiation area, and by using low dynamic transducer mass. Since the principle of operation requires for each transducer that its motion be influenced by its own radiation load, it is necessary to control each transducer’s motion so that the desired radiation pattern is achieved. This is done by a filtered-X feedforward LMS adaptive controller.
Vertical array performance in shallow water with a directional noise field
Authors: Yoo Kwang , Yang T. C.
Published: October 2005

The performance of a vertical array for source localization and for target detection (array gain) is studied in shallow water under a directional noise field. The acoustic environment consists of a downward refractive sound-speed profile. At mid (e.g., 500 Hz) frequencies the vertical directionality of the surface generated noise exhibits a notch near the signal arrival direction, i.e., which is close to horizontal for a submerged source. The ability of the beam filter in rejecting directional noise has been previously demonstrated using conventional beamforming. The same capability is carried over into full field processing by using matched-beam processing which is an equivalent of matched-field processing conducted in the beam domain. It is shown with simulated data that matched-beam processing incorporating a beam filter of 10 deg enhances the array output signal-to-noise ratio (array gain) by more than 5 dB compared with conventional beamforming and matched-field processing. For white noise, matched-field processing yields a higher peak-to-sidelobe ratio than matched-beam processing with a beam filter. For directional noise, matched-beam processing with a beam filter yields better results than matched beam processing using a minimum variance correlator. The noise field in the background ambiguity surface (the sidelobes) has been suppressed by the beam filter.
Simulated performance of an acoustic modem using phase-modulated signals in a time-varying, shallow-water environment
Authors: Bjerrum-Niese Christian , Bjo/rno/ Leif
Published: October 2005

Underwater acoustic modems using coherent modulation, such as phase-shift keying, have proven to efficiently exploit the bandlimited underwater acoustical communication channel. However, the performance of an acoustic modem, given as maximum range and data and error rate, is limited in the complex and dynamic multipath channel. Multipath arrivals at the receiver cause phase distortion and fading of the signal envelope. Yet, for extreme ratios of range to depth, the delays of multipath arrivals decrease, and the channel impulse response coherently contributes energy to the signal at short delays relative to the first arrival, while longer delays give rise to intersymbol interference. Following this, the signal-to-multipath ratio (SMR) is introduced. It is claimed that the SMR determines the performance rather than the signal-to-noise ratio (SNR). Using a ray model including temporal variations of the shallow-water environment, the performance of the acoustic modem may be estimated. Simulations indicate that optimum performance is not necessarily found at receiver depths yielding the maximum total signal level, since the SMR may correspondingly be low due to strong intersymbol interference. [Work sponsored by the Danish Technical Research Council.]
Development of the acoustic packet data relay communication system and the results of its sea trial
Authors: Ochi Hiroshi , Shimura Takuya , Amitani Yasutaka , Tsuchiya Toshio
Published: October 2005

In order to recover the data obtained by various sensors deployed in the ocean, a study was made concerning the acoustic digital data communication system [Ochi et al., Proc. Meeting Marine Acoust. Soc. Jpn., pp. 85–86 (1996) (in Japanese)]. The data communication system was constructed by up to 99 of the same type of equipment in the area, and its specifications are: a half-duplex communication, FSK modulation, a 2500bps data rate, HDLC (high-level data link control procedure) protocol packet transmission, CRC (cyclic redundancy check) code, and frame retransmission for error detection/correction. The sea trial of this system was done at about a 4000-m depth area. Three sets of equipment were deployed in the ocean, and one of them hangs from the ship. Then, relay data transmission, among the three sets of equipment, was carried out. The detail of that sea trial will be shown at this presentation.
The effectiveness of a thin wedge design anechoic lining for long-time signature measurements.
Authors: Boober Walter H. , Emery Scott
Published: October 2005

A thin wedge design anechoic lining has proven to be very effective for long time signature measurements at frequencies above 10 kHz. Partial treatment on five of six surfaces in a 60×40×35-ft3 depth tank resulted in accurate transfer functions of a test transducer using late sample delays for long-time signature waveforms. Comparison of data resulting from delays prior to wall/surface reflections with delays as late as 200 ms revealed negligible contribution, if any, from reflections. The ‘‘reflection’’ data when graphed over ‘‘free-field’’ data were indistinguishable. Tests were run using a directional array projector and a horizontally omnidirectional projector. The hydrophone was an H-52; a 5.1-cm vertical line array, omnidirectional in the horizontal plane. This allowed some discrimination from surface and bottom reflections. Reflections from the untreated wall were strong contributors while using the omnidirectional projector and were revealed in radiation patterns of the directional array. These tests under real world everyday measurement conditions demonstrate the effectiveness of the panels for long pulse times with late delay sampling in constrained boundaries.
Acoustic thermometry of ocean climate
Authors: Munk Walter H.
Published: October 2005

The purpose of ATOC is to study climate variability in the oceans using three related techniques: (i) satellite altimetry, (ii) acoustic thermometry, and (iii) climate modeling. Satellite altimetry is related to ocean temperature by thermal expansion (melting glaciers are a secondary factor) with each mm of sea level rise corresponding to 15 to 30 mJ/m2 of stored thermal energy. Acoustic thermometry is associated with the temperature dependence of the speed of sound, and relates changes in the interior heat storage with small changes in acoustic travel times (10 ms at 5000 km, say). The THETIS experiment (Send, 1995; Menemenlis and Wunsch, 1996) in the western Mediterranean gives consistent results for the seasonal heat storage when all three techniques are combined; model prediction alone does not account for the observed changes. Fu and associates at JPL have reported on the changes in sea level measured by TOPEX-POSEIDON for the period 1992–5. For a global spatial average they obtain an astounding (but preliminary) 6 mm/year, but with regional departures by an order of magnitude. Some of the departures can be related to decadal variability. A comparison between the satellite and acoustic measurements is needed for interpretation. [Work supported by SERDP/ARPA.]
Acoustic thermometry of ocean climate. A description of the acoustic network
Authors: Mercer James A. , Howe Bruce M. , Dushaw Brian D. , Spindel Robert C. , Worcester Peter F. , Colosi John A. , Cornuelle Bruce D. , Dzieciuch Matthew A. , Munk Walter H. , Birdsall Ted , Metzger Kurt
Published: October 2005

The ATOC acoustic feasibility network became functional in December 1995 following the installation of an acoustic source on Pioneer Seamount approximately 50 nm off the coast of Northern California. The current effort is part of the Marine Mammal Research Program Pilot Study. This paper describes the acoustic network of sources and receivers, including the augmentations to be made in summer 1996. The network was designed to take advantage of existing hydrophone arrays, while providing for maximum coverage of the North Pacific by the acoustic paths. The acoustical receptions currently being obtained are processed to obtain ‘‘dot plots’’ which show the arrival times and arrival angles of acoustical energy above a chosen signal-to-noise ratio. The ‘‘dot plot’’ histories demonstrate stable ray arrivals (albeit with significant amplitude fluctuations) for even the longest propagation ranges of 5 Mm. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
On the acoustic forward problem for basin-scale ocean acoustic tomography
Authors: Colosi John A. , Cornuelle Bruce D. , Dzieciuch Matthew A. , Munk Walter , Worcester Peter F. , Dushaw Brian , Howe Bruce , Mercer James , Spindel Robert C.
Published: October 2005

For the ATOC program two dense vertical-line arrays (VLA) centered on the sound-channel axis and located off of the islands of Hawaii and Christmas, and several bottom-mounted horizontal arrays located around the North Pacific have recorded basin-scale acoustic transmissions emminating from a bottom mounted source located on Pioneer Seamount since December 1995. Coherent ‘‘raylike’’ wavefronts with small travel-time fluctuations are observed at these stations ( ranges 1 to 5 Mm). The ‘‘ray- like’’ arrivals can be unambiguously identified with specific ray paths using standard climatologies so that travel times of these ray arrivals may be used to infer oceanic variability such as tidal current and average heat content. The ‘‘raylike’’ arrivals recorded on the bottom receivers appear to be associated with ray paths whose lower turning points are several hundred meters above the receiver. Vertical leakage of acoustic energy below the ray turning point from internal waves and/or diffraction effects are insufficient to explain these observations. At the VLAs, the ‘‘raylike’’ arrivals are followed by a complex ‘‘modelike’’ finale. Resolved modal arrivals show mode 1 to be fairly adiabatic, yet nonadiabaticity increases rapidly with increasing mode number. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
Comparison of ATOC heat content estimates with combined estimates from a general circulation model and TOPEX/POSEIDON altimetry
Authors: Menemenlis Dimitris , Stammer Detlef , Wunsch Carl , Hill Chris , Marshall John
Published: October 2005

To study the role of the oceans in climate, weather, and other ocean–atmosphere phenomena, one needs to observe a global-scale turbulent fluid that is opaque to electromagnetic radiation. Acoustic tomography and satellite altimetry provide complementary observational technologies for this purpose: Tomography provides path-averaged heat content estimates with a degree of vertical resolution commensurate with the number of resolved acoustic rays or modes; altimetry provides depth-integrated heat content estimates with good horizontal coverage but with additional contributions from the wind-driven circulation and from uncertainties in the mass and salt budgets. These data, in combination with the dynamical descriptions embodied in general circulation models, are powerful tools for monitoring large-scale oceanic variability. As a first step toward the demonstration of a complete system, heat content estimates obtained by the acoustic thermometry of ocean climate (ATOC) project are compared with those obtained by constraining the MIT ocean circulation model with TOPEX/POSEIDON altimeter data. This work extends a technique that has already been successfully deployed to make basin scale state estimates in the Western Mediterranean. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
Acoustic observations of internal-wave strength in the Mid-Pacific in 1989 and 1996
Authors: Flatté Stanley M. , Colosi John A. , Dzieciuch Matthew A. , Worcester Peter F.
Published: October 2005

Depth diffusion of acoustic energy in the finale of acoustic pulses has been observed for transmissions of 1 Mm (Slice89, Mid-Pacific), 3.5 Mm (ATOC, California to Hawaii), and 5.1 Mm (ATOC, California to Christmas Island). This depth diffusion is a measure of the strength of internal waves in the main thermocline. A measure of the strength of internal waves is defined as the variance of displacement at a reference buoyancy frequency of 3 cph. The standard Garrett–Munk spectrum has a strength of 50 m2. In the case of Slice89, an internal-wave strength of 25 (+/−) 10 m2, was observed (July 1989). Internal-wave strength will be presented for the two ATOC location paths, for dates beginning in November 1995. Information from identifiable time fronts in the early-arriving part of the pulse will also be presented. [Work supported by ONR and by the Strategic Environmental Research and Development Program through ARPA.]
Estimation of internal wave strength from mode space source localization
Authors: Heaney Kevin D. , Colosi John , Kuperman William A.
Published: October 2005

Internal waves have been shown to cause significant mode coupling for long-range acoustic transmissions [Colosi and Flatte, J. Acoust. Soc. Am. (in press)]. This coupling produces a variance and bias in a modal arrival time difference range estimator and a mode space depth estimator. The bias and variance induced by internal wave coupling is quantifiable. An inversion is therefore possible for the background strength of the internal wave field. The structure of the mode arrival time bias provides information on the depth of maximum internal wave activity. The success of the depth estimator reveals the limit of internal wave-induced mode coupling and places an upper bound on the energy in the Garrett–Munk spectrum. Broadband long-range simulations through internal wave realizations will be presented, quantifying the effect. Results from experimental data along different propagation paths (AET and ATOC95) will be presented, and an estimate of the internal wave strength parameter will be given for each.
Twin broadband waveform generation using a nonlinear acoustic source
Authors: Metzger Kurt , Birdsall Ted
Published: October 2005

The ATOC AST measurements in July 1996 used simultaneous broadband waveforms in bands near 28 and 84 Hz to study frequency-dependent differences in long-range propagation. The low band was below the normal operating range of the Hydroacoustics HLF6 transducer. The nonlinearity of the source, driven exceedingly hard in the low band, generated the high band waveform. Both m-sequence based and prescription FM waveforms were used. The desired level in each band was 135 W. This paper describes the procedures used to generate the transmitted waveforms and to process the receptions for multipath travel times and modal analysis. [Work supported by the Strategic Environmental Research and Development Program through ARPA.]
Modeling issues in the simulation of long-range ocean acoustic pulse transmissions
Authors: McDonald B. Edward , Kuperman W. A. , Heaney Kevin D.
Published: October 2005

Pulse propagation from a wideband source in the ocean sound channel is being modeled theoretically and numerically in the time domain for comparison with ATOC transmissions on a 3-Mm path between California and Hawaii. The physics of pulse dispersion in a waveguide is addressed using stationary phase approximations for integrals over frequency. For a parabolic sound slowness profile the basic theory admits a closed analytic solution for an impulsive source using the WKB approximation. Inclusion of realistic SSPs with time- and range-dependent fluctuations (primarily internal waves) is accomplished by a combination of parabolic equation modeling and modal analysis. Attempts to include realistic fluctuations in the stationary phase approximation are discussed. [Work supported by NRL and ONR and by the Strategic Environmental Research and Development Program through ARPA.]
Source localization at basin scale ranges from a small array
Authors: Heaney Kevin D. , Kuperman William A.
Published: October 2005

Application of time domain filtering to acoustic signals received at distances of greater than 3000 km has allowed oceanographers to extract modal information for a number of modes greater than the number of elements in the array. A model-based iterative algorithm has been developed to estimate the range of the source from the normal mode arrival time differences. The algorithm was applied to the acoustic engineering test of the acoustic thermometry of the ocean climate (ATOC) project. The modal amplitudes were used to then determine the source depth successfully. Successful localization implies that the source information has not been lost completely. This places an upper bound on the amount of internal wave-induced mode coupling that can be occurring. The bias in the range estimator is caused by internal wave-induced mode coupling and can be used as a measure of the internal wave strength. Results from the ATOC95 experiment at larger ranges (3500 and 5500 km) will be presented as well.
New Zealand ATOC path stability test results
Authors: Bold Gary E. J. , Tindle Christopher T. , Guthrie Michael K. , Marrett Ralph
Published: October 2005

Signals were recorded at a site off the New Zealand coast during the 1994 ATOC Acoustic Engineering Test (AET) using a single hydrophone at the SOFAR axis suspended from a drifting sonobuoy. The receptions recorded were limited to a 2-day period due to weather and logistic constraints, but those analyzed showed considerable variability in structure from transmission to transmission. This path is particularly interesting because of its length (10 Mm) and its transequatorial nature. A moored, autonomous system was deployed in early 1996 off the New Zealand coast to acquire data over several months to investigate signal variability further. The source was on the Pioneer Seamount, and the single hydrophone moored at the SOFAR axis channel depth. These data and their analysis will be presented and discussed.
Establishing realistic requirements for sonar transducers used in ocean acoustical tests
Authors: Hugus George D. , Ivey Larry E.
Published: October 2005

Unrealistic requirements are often placed on sonar transducers employed in ocean acoustical tests. This is because projectors and hydrophones are often the last components considered when system requirements are established. Acoustical systems for performing these tests are typically designed for one application, but are frequently used for additional tests. This can cause conflicting system requirements and place constraints on the transducer design which result in failure to meet test objectives and redesign of the whole system. This paper provides an approach for first establishing realistic transducer design requirements which, in reality, drive those for the complete system. Experience with important transducer acoustical parameters such as operating frequencies, sensitivity and transmitting response, directivity, dynamic range, self-noise, and flow noise is discussed. Also discussed are experiences with at-sea effects of system deployment while stationary or maintaining a constant velocity, operating depth, cable dynamics, hydrodynamically configured tow bodies, and costs.
Electrical equivalent circuit of a thick Langevin-type flexural transducer
Authors: Tamura Takeshi , Koike Yoshikazu , Ueha Sadayuki
Published: October 2005

Since there are two vibration components at a mechanical output terminal of a thick flexural transducer, that is, lateral and rotational components, corresponding electrical ports have to be provided in the electrical equivalent circuit. A load applied to the transducer also has to be considered separately corresponding to each vibration component. To treat this situation with the electrical equivalent circuit, an analytical solution, namely, Timoshenko’s beam theory given by Miklowitz and the piezoelectric equation, is applied to calculate the free vibration mode and the electrical equivalent components of the transducer. Using this derived equivalent circuit, the behavior of the loaded flexural transducer is experimentally studied to prove the validity of the proposed circuit. This is the first trial to derive such an equivalent circuit that can treat two vibration components simultaneously.
A sonar application of 1-3 piezocomposite material
Authors: Geil Fred G. , Gentilman Richard , Serwatka William , Webman Kenneth
Published: October 2005

Injection molded piezocomposite materials have significant potential for improving the performance of Navy and civilian acoustic systems. Specifically, a 1-3 configuration based on PZT exhibits attractive properties for hydrophone array systems where the elements are many and/or small. An array of 1-3 composite hydrophones has been manufactured and tested as a potential replacement for a currently used 0-3 composite (Piezo-rubber) hydrophone array developed for a high frequency sonar. For this application, several experimental composite panels have been manufactured from injection molded PZT-5H and PZT-4 ceramic, each of which contains 20 or 40 elements. Acoustic modeling and test results have been obtained for two configurations of interest: the array panel alone; and the panel installed in a housing similar to the finished hydrophone module. Results will be presented which include: predictions of sensitivity and phase response; predictions of self-noise candidate material, including future designs with smaller elements; acoustic measurements (sensitivity, beam patterns, relative phase) for the test panels alone; acoustic measurements for the panels mounted in the housing. A companion paper (R. Y. Ting) will cover the sensitivity of these measurements to changes in pressure and temperature. In conclusion, trade-off factors for choosing various hydrophone materials will be suggested.
High-power, low-frequency magnetostrictive TRIPODE and JANUS projectors
Authors: Dubus Bertrand , Bigotte Patrice , Claeyssen Frank , Lhermet Nicolas , Grosso Gilles , Boucher Didier
Published: October 2005

Terfenol-D is a magnetostrictive rare-earth alloy having giant dynamic strain capabilities and low Young’s modulus compared to PZT ceramics. Therefore, terfenol-D is a good candidate for realizing high-power, low-frequency projectors for oceanography or sonar. This paper presents two magnetostrictive projectors which have been recently designed and realized for the French Navy. The first one is a tonpilz transducer (TRIPODE) which uses three parallel terfenol-D rods as drivers. Magnetic dc bias and excitation are produced by coils. The drivers are surrounded by a cooling liquid continuously stirred by an electrical device. In water, the maximal acoustical power reaches 4 kW at 1.1 kHz. TRIPODE volume and mass are, respectively, 22 dm3 and 60 kg. The second one is an axisymmetrical double-ended longitudinal vibrator (JANUS) having a central terfenol-D rod. Permanent magnets provide magnetic dc bias. A specific thermal analysis has been performed to enable heat evacuation by natural convection. Models predict an acoustical power of 1.5 kW at 400 Hz. JANUS volume and mass are, respectively, 25 dm3 and 100 kg. For both transducers, various results obtained at the design stage during realization and experiments are provided.
Development of combustive sound source for array and towed deployment
Authors: Wilson Preston S. , Muir Thomas G.
Published: October 2005

The combustive sound source (CSS) utilizes the combustion of a gaseous fuel-oxygen mixture to produce very low-frequency signals. Various different deployment configurations previously reported adapt CSS for use in the water column, on the ocean bottom, and on the earth’s surface [Wilsonet al., IEEE J. Ocean. Eng. 20, 311–320 (1995)]. There has been recent work in the development of a linear horizontal array consisting of up to four 2.5-liter elements. Measured acoustic signatures and spectra in the 10- to 1000-Hz band, which are produced by the combustion of methane and oxygen mixtures, are reported for individual elements and 2-, 3-, and 4-element arrays. Comparisons are made with the array performance of similar sources such as the air gun and sparker, as well as to model predictions. Finally, a prototype towed version of the single element CSS has been developed using an on-board electrolytic gas generator that enables the combustion of hydrogen. Signatures and spectra produced by the towed CSS will be compared to stationary CSS data and to other similar towed sources. [Work supported by the U.S. Navy Office of Naval Research.]
Control of segment interactions in flexural shell transducers
Authors: Benthien George W. , Gillette David L. , Barach Don
Published: October 2005

Many flexural shell transducers are constructed of independently driven segments. It has been observed that this construction often leads to undesirable nulls and peaks in the acoustic response arising from acoustic interaction of the segments. Methods for minimizing the effects of these interactions will be presented along with supporting modeling results. [Work supported by SPAWAR, Code 182.]
The development of a very large, dense-packed, two-dimensional, ultrasonic imaging array
Authors: Benjamin Kim C.
Published: October 2005

The design, construction, and measured results for a prototype module of probably the world’s largest dense-packed, two-dimensional, ultrasonic (1.5-MHz) receive array is described. Containing over a quarter million diced elements, and a centrally located, constant beamwidth, spherical cap projector, the complete array was to consist of 25 modules, of which the central module is described. The individual receive element dimensions were (0.91×0.91×0.89) mm, with a center to center spacing of 1.07 mm. The ultrasonic spherical cap projector element had a 29-mm radius of curvature and an active angular aperture of 40 deg. Both projector and receive elements were designed to achieve a minimum 3-dB beamwidth of 30 deg at 1.5 MHz. In both cases the active material was piezoceramic. This presentation will discuss the various material tradeoffs associated with the selection of the: (1) active layer, (2) backing layer, (3) mechanical, and (4) electrical connections. Also the issues of dicing and back filling of the inter element interstices will be addressed. Measured acoustic calibration results for a small subset of receive elements and the projector will be presented.
Aerodynamic problems arising in high-speed train development
Authors: Kohama Yasuaki , Tanaka Giichi , Oizumi Shouichi
Published: October 2005

The aerodynamic problem, which has not been a serious one previously in the field of train technology, is now becoming serious as the train speed is increased: aerodynamic noise, aerodynamic drag, train oscillation, and structural damage, etc. Of these, the present investigation deals with the aerodynamic problems concerned with the shapes of a nose coach and a pantograph, which are the most important portions to be improved in the train system as far as the train aerodynamics and noise are concerned. Using a recently constructed low-noise, low-turbulence small wind tunnel, systematic investigations have been conducted experimentally, and new shapes for those train components are being developed and suggested for future high-speed train systems. Especially, a detailed investigation was done for the insulator (Gaishi, in Japanese), and a low-noise insulator was developed.
Aeroacoustic noises radiating from a louver at an intake hole
Authors: Sagawa Akio , Matsuo Jun , Shibuya Masayuki , Kitayama Shigeru
Published: October 2005

This paper presents the wind tunnel test results for measuring aeroacoustic noises originating from several half-size models of a louver used at an air intake hole, which is often seen on the side plate of the rolling stock of a Japanese high-speed train. Based on the acoustic characteristics of the measured sounds radiating from the louver when an airflow passes by, the following conclusions are reached. (1) Aeroacoustic sounds radiating windward and leeward from a louver of standard type are significant, possibly caused by pressure fluctuation on the strips reinforcing the louver, which are fixed crosswise to partitioning strips and usually to an airflow. (2) Recommended countermeasures for strong and dipolelike sounds originating from the reinforcing strips are reducing the number of the strips, adopting a roundish shape like an ellipse for their cross sections, and fixing them somewhat inside, avoiding windy positions. (3) It is ascertained that rounding the right-angled edges, which are located windward and leeward, of the framework of an air intake opening has considerably desirable effects on both generated sounds and the capacity of the air intake.
Community noise model for train warning horn
Authors: Carman Richard A.
Published: October 2005

For public safety, freight and passenger trains are required to have audible warning devices to signal the approach of trains at grade crossings, and in case of an emergency, where there is a shared right-of-way or other possible public access to railroad tracks. Some communities have expressed a desire to reduce the need for sounding warning horns at grade crossings. Although very expensive, grade-separated railroad crossings are one means by which communities and railroads can reduce the need for horn blowing in populated areas. Efforts are being made to develop new grade crossing safety devices that reduce the need for horn blowing. However, use of warning devices such as horns or whistles to signal the approach of trains, especially at grade crossings, will probably remain a major source of railroad noise in most communities through which railroads pass. A noise prediction model is presented and compared with noise data measured for freight train locomotive horns at grade crossings. Horn sounding duration is included in the model, and its effect on time-weighted community noise descriptors such as Ldn is examined.
A method for predicting train noise in subway stations
Authors: Kang Jian
Published: October 2005

Subway stations are typically long enclosures, where classical room acoustic theory is inappropriate [J. Kang, J. Acoust. Soc. Am. 99 (1996)]. In this research, a computer model for predicting the temporal and spatial distribution of train noise in subway stations is developed [J. Kang, J. Sound and Vib. 194 (1996)]. The train is regarded as a series of sections, and the train noise distribution in a station is calculated by inputting the sound attenuation from a train section source in the subway system (i.e., the station and tunnel). This input can be obtained by physical scale modeling. The prediction in a subway station shows good agreement with the site measurements. A series of computations in the station demonstrates that: (1) the overall level of the train noise in the area near the end walls is slightly less than the other areas; (2) some conventional architectural acoustic treatments in the station are effective when a train is still in the tunnel but not as helpful when the train is already in the station; and (3) train noise typically decreases the speech transmission index of public address systems to below 0.5. [Work supported by MTRC, ORS, and COT.]
The propagation of high-speed train noise above an impedance ground
Authors: Li Kai Ming
Published: October 2005

Transportation noise sources are usually in motion. Previous analyses have simplified the problem by assuming a moving source either as a quasistationary point source or, in the case of traffic noise as a continuous line source problem. This assumption is valid for a vehicle traveling at low speed but is unlikely to be adequate for a source traveling at a non-negligible Mach number. A notable example is a high-speed train traveling in excess of 200 km h−1. In this paper, as a first approximation, the high-speed train is modeled as a moving monopole source above an impedance ground. Although the sound field due to a moving monopole source in an unbounded medium is well known, there is relatively little attention focused on a moving point source near to an impedance ground surface. Asymptotic analysis has been conducted to derive a closed-form analytic solution. The project described in this paper is a canonical problem. The solution (Green’s function) will be a building block for modeling noise propagation due to high-speed trains in future studies which includes, for example, a moving line source and a moving dipole, etc. [Work supported by EPSRC, UK.]
A measurement method of an oblique-incidence absorption coefficient
Authors: Suzuki Hideo , Okoshi Masaru , Shiroko Norio , Kido Ken’iti
Published: October 2005

It is said that the road surface has significant effects on road noise. For a proper evaluation of the effect of the road surface, it is important to develop a measurement method of the absorption coefficient for oblique as well as vertical incidence. A measurement method was developed that can be used in a hemianechoic room. A long strip of test material approximately 2 m in length and 0.5 m in width is placed on the floor of the room. A test noise is generated by a line array of loudspeakers which is placed above the floor and parallel to the test material. The distance from the material to the loudspeaker array is approximately 2 m. The position of the loudspeaker array is moved on the circumference so that the incidence angle may be changed while keeping the radius constant. The incident power is measured beforehand in an anechoic room which is proportional to the sound pressure squared. The absorbed power is measured by use of the sound intensity method. The measurement points of the intensity are on a smaller semicircle (approximately 0.5 m) with the same center as the test material. The absorption coefficient is given by the ratio of the absorbed power to the incident power.
Efficiency of noise barriers with an acoustically soft cylindrical edge
Authors: Okubo Tomonao , Fujiwara Kyoji
Published: October 2005

It is well known that an absorptive obstacle installed on the edge of a noise barrier can improve sound shielding efficiency without increasing its height. In the present study, efficiency of the noise barrier with a ‘‘soft’’ cylindrical edge is investigated. Soft means a surface on which the sound pressure is zero, but it is difficult for traditional materials to realize this surface. It is shown, by numerical and experimental analysis in a two-dimensional sound field, that the ‘‘Waterwheel cylinder’’ approximately realizes a soft surface. The Waterwheel consists of acoustic tubes arranged radially; thus the acoustical properties of the Waterwheel’s surface (i.e., the sound pressure at the open ends of the tubes) depend on the relation between the depths of the tubes and the wavelengths. Then sound shielding efficiency of a half-plane and a barrier sitting on the ground with the Waterwheel edge has been investigated. The results show that the Waterwheel on the edge improves the noise shielding efficiency by more than 10 dB in a certain frequency range, although the Waterwheel decreases the efficiency of a barrier in another range. The effect depends strongly on the frequency, as the sound pressure on the surface of the Waterwheel does.
Scale model investigations into the insertion loss of screens under the influence of wind
Authors: Rasmussen Karsten B. , Galindo Arranz Marta
Published: October 2005

A hard screen on an absorbing ground is investigated experimentally and theoretically under the influence of wind. The experimental data are the result of model experiments in a 1:25 scale model within a wind tunnel. The sound propagation is measured using a triggered spark source and averaging on a power basis in the frequency domain. The meteorological data representing the wind conditions have been determined by means of hot-wire anemometry in positions on both sides of the screen as well as directly over the screen. The measured data are compared with calculated results from PE calculations [taking the screen into account as suggested by E. Salomons, J. Acoust. Soc. Am. 95, 3109–3117 (1994)] and from an alternative ray oriented approach based upon the use of diffraction theory for the screen. The use of the scale model approach makes it possible to perform detailed comparisons of range-dependent measured profiles and calculated results. This reveals new insight in the insertion loss of screens under realistic conditions and provides a basis for future investigations into the influence from turbulent eddies generated at the top of the screen.
Experimental results for transmission of a finite-amplitude, focused sound beam at a curved interface between two media
Authors: Makin Inder Raj S. , Everbach E. Carr , Hamilton Mark F.
Published: October 2005

Transmission of an intense focused sound beam through two different liquids separated by a curved interface was investigated experimentally. The acoustic field was generated by a 2.25-MHz tone burst from a focused source of radius 19 mm and focal length 159 mm. Measurements of propagation curves and beam patterns were made using a PVDF needle hydrophone. The source was placed in water, the first liquid, and either lamp oil (cwater/coil=1.08) or a 50% glycerin–water mixture (cwater/cmixture =0.85) was used as the second liquid. Curvature at the interface between the water and the second liquid was controlled by using a thin (≊40 μm) polyether polyurethane membrane. Both concave or convex curvatures, with radii varying from 90 mm to infinity (plane interface), were achieved by varying the hydrostatic pressure between the two liquid chambers. Measurements were compared with theory, presented earlier [Makin, J. Acoust. Soc. Am. 95, 2864(A) (1994)], based on the nonlinear parabolic (KZK) wave equation. Reasonably good comparison between theory and experiment was observed for the first four harmonics generated in the incident and transmitted fields for interfaces with various curvatures, and located in either the pre-focal or post-focal regions. [Work supported by NSF.]