Volume 124, Issue 3, September 2008
- jasa express letters
- acoustical news—usa
- acoustical standards news
- book reviews
- reviews of acoustical patents
- letters to the editor
- education in acoustics 
- nonlinear acoustics 
- aeroacoustics, atmospheric sound 
- underwater sound 
- ultrasonics, quantum acoustics, and physical effects of sound 
- transduction 
- structural acoustics and vibration 
- architectural acoustics 
- acoustical measurements and instrumentation 
- acoustic signal processing 
- physiological acoustics 
- psychological acoustics 
- speech production 
- speech perception 
- speech processing and communication systems 
- music and musical instruments 
- bioacoustics 
Index of content:
- JASA EXPRESS LETTERS
124(2008); http://dx.doi.org/10.1121/1.2972156View Description Hide Description
124(2008); http://dx.doi.org/10.1121/1.2963087View Description Hide Description
Fluctuations of the low frequency sound field in the presence of an internal solitary wave packet during the Shallow Water ’06 experiment are analyzed. Acoustic, environmental, and on-board shipradar image data were collected simultaneously before, during, and after a strong internal solitary wave packet passed through the acoustic track. Preliminary analysis of the acoustic wave temporal intensity fluctuations agrees with previously observed phenomena and the existing theory of the horizontal refraction mechanism, which causes focusing and defocusing when the acoustic track is nearly parallel to the front of the internal waves [J. Acoust. Soc. Am., 122(2), pp. 747–760 (2007)].
Mid-frequency sound propagation through internal waves at short range with synoptic oceanographic observations124(2008); http://dx.doi.org/10.1121/1.2963097View Description Hide Description
Preliminary results are presented from an analysis of mid-frequency acoustic transmission data collected at range during the Shallow Water 2006 Experiment. The acoustic data were collected on a vertical array immediately before, during, and after the passage of a nonlinear internal wave on 18 August, 2006. Using oceanographic data collected at a nearby location, a plane-wave model for the nonlinear internal wave’s position as a function of time is developed. Experimental results show a new acoustic path is generated as the internal wave passes above the acoustic source.
Intensity fluctuations of midfrequency sound signals passing through moving nonlinear internal waves124(2008); http://dx.doi.org/10.1121/1.2968294View Description Hide Description
The fluctuations of intensity of broadband pulses in the midfrequency range propagating in shallow water in the presence of intense internal waves moving approximately along the acoustic track are considered. These pulses were received by two separate single hydrophones placed at different distances from the source ( and ) and in different directions. It is shown that the frequency spectra of the fluctuations for these hydrophones have different predominating frequencies corresponding with the directions of the acoustic track. Comparisons of experimental results with theoretical estimates demonstrate good consistency.
124(2008); http://dx.doi.org/10.1121/1.2963043View Description Hide Description
Mid-frequency sound propagation was measured at ranges in shallow water in order to investigate intensity statistics. Warm water near the bottom results in a sound speed minimum. Environmental measurements include sediment sound speed and water sound speed and density from a towed conductivity-temperature-depth chain. Ambient internal waves contribute to acoustic fluctuations. A simple model involving modes with random phases predicts the mean transmission loss to within a few dB. Quantitative ray theory fails due to near axial focusing. Fluctuations of the intensity field are dominated by water column variability.
Mid-frequency acoustic propagation in shallow water on the New Jersey shelf. II. Intensity fluctuation124(2008); http://dx.doi.org/10.1121/1.2968295View Description Hide Description
The scintillation index and the intensity cumulative distribution function of mid-frequency sound propagation are presented at ranges of 1–9 in a shallow water channel. The fluctuations are due to water column sound speed variability. It is found that intensity is only correlated over a narrow frequency band (50–200 Hz) and the bandwidth is independent of center frequency and range. Furthermore, the intensity probability distribution peaks at zero for all frequencies, and follows an exponential distribution at small values.
Observed limiting cases of horizontal field coherence and array performance in a time-varying internal wavefield124(2008); http://dx.doi.org/10.1121/1.2947630View Description Hide Description
Using a moored source and horizontal/vertical line array combination, horizontal coherence properties of high signal to noise ratio signals have been measured. Internal waves in the area of the measurement created moving episodic sound-speed anomaly structures, influencing coherence length. Measured horizontal coherence scales for ranged from 5 to 20 acoustic wavelengths, and were inversely related to the sound-speed anomaly strength. Horizontal field properties were compared with fields computed using modal decompositions of the vertical signals. The comparison allows azimuthal field coherence properties to be studied apart from normal-mode interference effects.
124(2008); http://dx.doi.org/10.1121/1.2968304View Description Hide Description
Temporal coherencies are compared for individual pulse arrivals of 100 and centered broadband signals propagating through identical shallow channels during periods of low and high internal wave energy. All modes are clean, distinct in time, and remarkably coherent . A near continuum of modes is observed for the signal with much shorter coherence times. Higher order modes are less coherent. Internal wave scattering appears to dominate the signals, whereas bottom scattering also randomizes the signal. Observations are consistent with similar measurements for this and other sites for intermediate frequencies.
124(2008); http://dx.doi.org/10.1121/1.2963188View Description Hide Description
The Shallow Water Experiment 2006 was conducted off the coast of New Jersey in the summer of 2006. Defence Research and Development Canada—Atlantic performed a series of experiments designed to validate the use of rapid environmental assessment tools and methods to improve active sonar performance predictions. The sensitivity of acoustic propagation to a varying or uncertain environment is determined by examining the relative change of acoustic pressure caused by environmental variability, using the method described recently [Dosso et al., J. Acoust. Soc. Am.121, 42 (2007)]. The variability of the modeled environmental parameters is based on measured and estimated oceanographic and geoacoustic properties. The resulting sensitivity is compared to measured transmission loss data at .
124(2008); http://dx.doi.org/10.1121/1.2963038View Description Hide Description
Knowledge of sediment sound speed is crucial for predicting sound propagation. During the Shallow Water '06 experiment, in situ sediment sound speed was measured using the Sediment Acoustic-speed Measurement System (SAMS).SAMS consists of ten fixed sources and one receiver that can reach a maximal sediment depth of . Measurements were made in the frequency range . Signal arrival times and propagation distances were recorded, from which sediment sound speed was determined. Preliminary results from three deployments show that SAMS was capable of determining sediment sound speed with uncertainties less than 1.6%. Little dispersion in sediment sound speed was observed.
124(2008); http://dx.doi.org/10.1121/1.2961404View Description Hide Description
The existence of acoustic velocity dispersion and frequency dependence of attenuation in marine sediments is investigated using in situ measurements from a wideband acoustic probe system during the Shallow Water 2006 experiment. Direct-path pulse propagation measurements show evidence of velocity dispersion within the frequency band at two silty-sand sites on the New Jersey Shelf. The measured attenuation in dB/m shows linear frequency dependency within the frequency band. The measured velocity dispersion and attenuation curves are in good agreement with those predicted by an extended Biot theory [Yamamoto and Turgut, J. Acoust. Soc. Am.83, 1744–1751 (Year: 1988)] for sediments with a distribution of pore sizes.
Observations of the R reflector and sediment interface reflection at the Shallow Water ’06 Central Site124(2008); http://dx.doi.org/10.1121/1.2963048View Description Hide Description
Acoustic bottom-interacting measurements from the Shallow Water ’06 experiment experiment (frequency range ) are presented. These are co-located with coring and stratigraphic studies showing a thin higher sound speed layer overlaying a thicker () lower sound speed layer ending at a high-impedance reflector (R reflector). Reflections from the R reflector and analysis of the bottom reflection coefficient magnitude for the upper two sediment layers confirm both these features. Geoacoustic parameters are estimated, dispersion effects addressed, and forward modeling using the parabolic wave equation undertaken. The reflection coefficientmeasurements suggest a nonlinear attenuation law for the thin layer of sandy sediments.
124(2008); http://dx.doi.org/10.1121/1.2963093View Description Hide Description
This paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of during the Shallow Water 2006 experiments. A ray-tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties. The ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment. The sediment sound speed and thickness estimates are consistent with in situ measurements and matched-field inversion results of longer-range data from the experiment.
124(2008); http://dx.doi.org/10.1121/1.2963095View Description Hide Description
This paper presents results of a range-independent perturbative inverse approach applied to data from the Shallow Water Experiment 2006. The inversion technique is based on a linearized relationship between sound speed in the sediment and modal eigenvalues. Horizontal wave numbers were estimated from data collected from two distinct source/receiver tracks oriented along and across the shelf. The specific inversion algorithm used is based on qualitative regularization and uses known information about the environment to constrain the solution. Locations of the R reflector and other layering information are used as a priori information for the inversion to emphasize the layered structure of the sediment.
124(2008); http://dx.doi.org/10.1121/1.2960974View Description Hide Description
Combustive sound source (CSS) data collected on single hydrophone receiving units, in water depths ranging from , during the Shallow Water 2006 experiment clearly show modal dispersion effects and are suitable for modal geoacoustic inversions. CSS shots were set off at depth in of water. The inversions performed are based on an iterative scheme using dispersion-based short time Fourier transform in which each time-frequency tiling is adaptively rotated in the time-frequency plane, depending on the local wave dispersion. Results of the inversions are found to compare favorably to local core data.
124(2008); http://dx.doi.org/10.1121/1.2960977View Description Hide Description
Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collected on two L arrays separated by from a single multi-frequency tow suggest small horizontal environmental variability. Values for the sound speed structure of the seabed are extracted by first applying a geo-acoustic inversion method to broadband and narrowband acoustic data from short-range sources. Then, a parabolic equation algorithm is used to properly include the bathymetry and sub-bottom layering. Finally, the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long-range transmission loss data in the band.
124(2008); http://dx.doi.org/10.1121/1.2960976View Description Hide Description
On the New Jersey continental shelf ambient sound levels were recorded during tropical storm Ernesto that produced wind speeds up to in early September 2006. The seabed at the position of the acoustic measurements can be approximately described as coarse sand. Differences between the ambient noise levels for the New Jersey shelf measurements and deep water reference measurements are modeled using both normal mode and ray methods. The analysis is consistent with a nonlinear frequency dependent seabed attenuation for the New Jersey site.
124(2008); http://dx.doi.org/10.1121/1.2963096View Description Hide Description
Measurements of excess attenuation from near-surface bubbles from the Shallow Water '06 experiment are reported. These are transmission measurements made over the frequency range , and they demonstrate a frequency, grazing angle, and wind speed dependence in attenuation. Data modeling points to bubble void fractions of order in effect for wind speeds . Simultaneous measures of wind speed made within 1.5 and of the open water experimental location differed by in their respective average; this has cautionary implications for empirical models for bubbleattenuation that are a strong function of wind speed.
124(2008); http://dx.doi.org/10.1121/1.2968296View Description Hide Description
Land-based seismic observations of double frequency (DF) microseisms generated during tropical storms Ernesto and Florence are dominated by signals in the band. In contrast, data from sea floor hydrophones in shallow water ( depth, off the New Jersey coast) show dominant signals in the ocean gravity-wave frequency band, , and low amplitudes from , suggesting significant opposing wave components necessary for DF microseism generation were negligible at the site. Florence produced large waves over deep water while Ernesto only generated waves in coastal regions, yet both storms produced similar spectra. This suggests near-coastal shallow water as the dominant region for observed microseism generation.
124(2008); http://dx.doi.org/10.1121/1.2960954View Description Hide Description
Acoustical array data from the Shallow Water Acoustics experiment was processed to show the feasibility of broadband mode decomposition as a preprocessing method to reduce the effective channel delay spread and concentrate received signal energy in a small number of independent channels. The data were collected by a vertical array designed at the Woods Hole Oceanographic Institution. Phase-shift Keying (PSK) -sequence modulated signals with different carrier frequencies were transmitted at a distance from the array. Even during a strong internal waves activity a low bit error rate was achieved.