Parameters Of Acoustic Signals Research Articles

Three dimensional parabolic equation modeling of acoustic intensity fluctuations due to internal wave phenomena.

During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (50–450 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf-break front and in an area where internal waves are known to occur. During the same time an internal wave, labeled event 44, passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both two and three dimensional) interference patterns. This presentation compares three dimensional modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship-born sensors to mimic the measured internal wave event. A modified version of the three dimensional Monterey–Miami parabolic equation (MMPE) code, which incorporates a user-defined sound speed field, is used. Measured and modeled intensity fluctuations are compared during dominating horizontal regimes such as refraction, focusing, and defocusing. Modal-dependent time-arrival analysis during the different horizontal regimes is examined. A sensitivity study of different sea-bottom properties is explored. [Work sponsored by the Office of Naval Research.]

Intensity fluctuations dominated by horizontal refraction during a strong nonlinear internal wave event.

During the Shallow Water 2006 (SW06) experiment, a J‐15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (100–500 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf‐break front and in an area where internal waves are known to occur. During the same time an internal wave, “Event 44,” passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both 2‐ and 3‐D) interference patterns. This presentation compares 3‐D modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship‐born sensors to mimic the measured internal wave event. A modified version of the 3‐D Monterey‐Miami parabolic equation (MMPE) code which incorporates a user‐defined sound s...

Three dimensional parabolic equation modeling of an internal wave event during Shallow Water 2006.

During the Shallow Water 2006 (SW06) experiment, a J‐15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (100–500 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf‐break front and in an area where internal waves are known to occur. During the same time an internal wave, “Event 44,” passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both two and three dimensional) interference patterns. Of specific interest are fluctuations of measured intensity preceding the internal wave’s arrival. Additionally, depth variability of the measured acoustic intensities can be attributed to a warm water intrusion coinciding with the internal wave event. This presentation shows recent modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship‐born sensors. A new version of the three‐dimensional Monterey–Miami parabolic equation code, which incorporates a user‐defined sound speed field, is used. [Work sponsored by the Office of Naval Research.]

Courtship behavior, communicative sound production and resistance to stress in Drosophila mutants with defective agnostic gene coding for LIMK1

To elucidate the role of one of the main elements of signal cascade of actin remodeling--LIM-kinase 1 (LIMK1)--in the control of animal behavior we studied the characteristics of courtship behavior, parameters of acoustic communicative signals and their resistance to heat shock (HS, 37 degrees C, 30 min) in Drosophila melanogaster males from the strain with mutation in locus agnostic (agn(ts3)) containing gene CG1848 for LIMK1. The data obtained was compared with the results of our previous similar investigation on wild type CS males (Popov et al., 2006). Flies were divided into 4 groups. The males of control groups were not subjected to heat shock. The rest of males were subjected to heat shock either at the beginning of larval development when predominantly mushroom body neuroblasts are dividing (groups HS1), or at the prepupal stage when the brain central complex is developing (groups HS2), or at the imago stage one hour before the test (groups HS3). All males were tested at the age of 5 days. Virgin and fertilized CS females were used as courtship objects. Comparison of control groups of the two strains--CS and agnostic--have shown that the mutation agn(ts3) has no influence on the main parameters of courtship behavior of intact (not subjected to HS) males (courtship latency, the rapidity of achieving copulation, courtship efficiency) but leads to lowering of their sexual activity, increase of duration of sound trains in the songs and to slight increase of rate and stability of working of singing pacemakers. Agnostic males in comparison to wild type males are more resistant to HS given 1 hour before the test. After HS their courtship intensity does not decrease and the main parameters of their courtship behavior and communicative sound signals in comparison tu wild type males either do not change, or appear to be even better stabilized. The frequency of distorted sound pulses (an indicator of frequency of impairments in the activity pattern of neuro-motor circuits of the singing center) decreases, and the rate and stability of pacemakers of the pulse and the sine songs increases. So, the sharply elevated LIMK1 and p-cofilin concentrations in the cells of agn(ts3) mutants, in comparison to wild type males, leading to derangement of learning and memory (Medvedeva et al., 2008) are accompanied by decline of motivation of males but do not seriously influence the neuro-motor coordination during singing. The higher resistance of characterictics of their behavior and communicative sound signals to heat shock is in agreement with the fact that the extremely high LIMK1 and P-cofilin concentrations in their cells go down to normal values after HS. At the same time the amyloid aggregations disappear and normally defective learning and memory are restore.

Mesoscale variations in acoustic signals induced by atmospheric gravity waves

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on acoustic signal parameters are analyzed in the present study. From the measurements of acoustic travel time fluctuations (periods 1 min-1 h) with distant receivers, the temporal fluctuations of the effective sound speed and wind speed are retrieved along different ray paths connecting an acoustic pulse source and several receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal phase velocities, and spatial scales) are estimated. The capability of acoustic tomography in estimating wind shear near ground is shown. A possible mechanism describing the temporal modulation of the near-ground wind field by ducted internal waves in the troposphere is proposed.

Acoustic tomographic study of the mesoscale coherent structures in the lower atmosphere

The results of acoustic tomographic monitoring of the coherent structures in the lower atmosphere and the effects of these structures on the acoustic signal parameters (travel time, duration and direction of propagation) are studied. From the measurements of acoustic travel time fluctuations (periods 1 min-1h) by a net of distanced receivers the temporal fluctuations of the effective sound speed are retrieved along different ray paths connecting a pulse source and the receivers. By using a coherence analysis of the fluctuations near spatially distanced ray turning points, the internal wave-associated fluctuations are filtered and their spatial characteristics (coherences, horizontal translation velocities, and spatial scales) are obtained. A possible explanation of the presence of the dominant periods in the observed mesoscale variations of the acoustic parameters, wind shears and turbulent fluxes of momentum near ground is done.

Incorporating environmental variability into received signal statistics

We have developed a Monte Carlo-based method for estimating the variability of acoustic signal parameters caused by uncertain ocean environments. The method begins with a physics-based model for the environmental properties and uses the maximum entropy (MaxEnt) method to construct probability density functions (pdf’s) describing the measured deviations from the model mean. Random realizations of environmental variability, with proper depth correlation, are constructed from the pdf’s and added to the mean model parameters. A parabolic equation code (ram) is used to propagate acoustic energy through each realization of the environment. Fourier synthesis is used to recreate the arrival structure. The method is demonstrated using measurements from the Strait of Gibraltar, which is a particularly complicated region dominated by strong tidal fluctuations and internal waves. During 1996, an international group carried out the Strait of Gibraltar Acoustic Monitoring Experiment (SGAME), in which detailed environmental and 250-Hz acoustic data were collected. Here, pdf’s of the received signal level are compared with results of the Monte Carlo method to demonstrate performance. [Gibraltar data and SVP model provided by Chris Tiemann (ARL:UT) and Peter Worcester (SIO). Work supported by ONR Undersea Signal Processing.]

Acoustic time delay estimation and sensor network self-localization: Experimental results

Experimental results are presented on propagation, coherence, and time-delay estimation (TDE) from a microphone array in an outdoor aeroacoustic environment. The primary goal is to understand the achievable accuracy of acoustic TDE using low-cost, commercial off-the-shelf (COTS) speakers and microphones. In addition, through the use of modulated pseudo-noise sequences, the experiment seeks to provide an empirical understanding of the effects of center frequency, bandwidth, and signal duration on TDE effectiveness and compares this to the theoretical expectations established by the Weiss-Weinstein lower bound. Finally, sensor network self-localization is performed using a maximum likelihood estimator and the time-delay estimates. Experimental network localization error is presented as a function of the acoustic calibration signal parameters.

Investigation of Strained States of Materials Using Fiber-Optic and Acoustic-Emission Methods

The paper reports on investigations of strained states and fracture of elements of thin-wall structures using acoustic and fiber-optic methods. A correlation has been found between the parameters of optical and acoustic signals on one side and strength characteristics of tested materials on the other. Combined tests using acoustic-emission and fiber-optic methods yield more reliable information about strained states of structural elements fabricated from various materials. These investigations can be used in developing diagnostic criteria for assessing technical conditions of thin-wall structures with the help of acoustic and fiber-optic methods.

Methodical approach to the experimental acoustic-emission evaluation of the crack resistance of structural materials

We develop a general approach to the determination of the characteristics of crack resistance of structural materials by the method of acoustic emission. This approach includes the procedure of selection of acoustic signals from cracks and the proper choice of the most efficient parameters of acoustic signals, the operating frequency of the receiving circuit of an acoustic-emission device, and the location of an acoustic-emission transducer. It is shown that, in the process of propagation of a crack, acoustic radiation is directed and the frequency band of emitted acoustic signals becomes narrower in the stage of subcritical crack growth.

DIVERGENCE IN MORPHOLOGY AND MATING SIGNALS, AND ASSORTATIVE MATING AMONG POPULATIONS OF CHORTHIPPUS PARALLELUS (ORTHOPTERA: ACRIDIDAE).

Three geographically widely separated populations of the grasshopper Chorthippus parallelus (Orthoptera: Acrididae) have been examined for morphological divergence, divergence in characteristics of the acoustic sexual signals of males, and assortative mating. Significant assortative mating existed between two of the three pairwise combinations of populations in multiple-choice tests. This may be caused by divergence in three of the four acoustic signal parameters measured. The populations also differed in morphology, including characters associated with signal production. The results are discussed in relation to theories for the origin of premating isolation, and it is argued that the observed divergence has developed rapidly, possibly indicating the action of selection. However, this selection could not have been caused by interactions with closely related taxa.

Remote acoustic sensing of manganese nodules on the ocean bottom

Experimental and theoretical investigations of acoustic properties of the deep-sea bottom covered with manganese nodules have been conducted. The objectives were (1) to study remote acoustic detection and outlining nodule deposits and (2) to investigate remote acoustic monitoring and estimation of the nodules abundance, mean size, and other parameters. Field experiments were conducted in four regions of the Pacific and Indian Oceans at the frequency range of 2–20 kHz. The field experiments have shown that availability of manganese nodules is displayed by an increase of both the sound reflectivity and scattering strength and by the appearance of their unusual, comparing nodules-free bottom, frequency-angular dependences. A theoretical model of sound scattering and reflection by a set of nodules laid on the bottom has been developed [A. V. Bunchuk and A. N. Ivakin, Sov. Phys. Acoust. 35(1), 5–11 (1989)] in which the explicit form of connection between characteristics of bottom reradiated acoustic signal and nodules parameters have been established. As a result, explanation became possible for all the obtained experimental data. The spatial distribution of amplitudes of signals reflected and scattered from the bottom can be mapped. Finally, real-time algorithms for the inverse problem solution were developed and their validity for adequacy was checked.

Adaptation au transfert de l’information sonore dans l’environnement. Rôle des paramètres de durée dans le cri de détresse de l’Étourneau (Sturnus vulgaris)

According to information theory, the extension of the duration parameters of acoustic signals increases their efficacity. The aim of our study was to test this hypothesis on distress call of a bird, the starling Sturnus vulgaris. Distress calls are high intensity alarm signals produced by birds when they are seized by a predator. Earlier studies revealed that frequency modulation constitutes an important feature of distress calls for triggering responses. The coding-decoding process is thus precisely defined. On the contrary, the coding of duration parameters seems imprecise since individuals produce distress calls of variable length. As predicted by the information theory, our experiments show that longer signals are more efficient than shorter ones. An explanation is that an increase in duration improves the signal resistance against degradation occuring during transmission through the environment. Our experiments indicate that signal recognition is affected by a noisy environment, particularly when noise overlaps a part of the signal. The greater the overlapping, the lower the signal recognition, independently of the position of the noise (at the beginning or the end of the signal). Consequently, to improve message efficiency in the case of transmission through a noisy environment, birds must increase the signal duration. The flexibility of duration parameters in the coding process gives birds the possibility of adapting their distress signals to different conditions of propagation.

Acoustic in situ monitoring of excimer laser ablation of different ceramics

Measurements of excimer laser generated acoustic transients were performed both on the back surface of various ceramic samples and in the surrounding gas. Several techniques of acoustic signal analysis were used to study the correlation between acoustic signal parameters and the ablation rate. The technique based on the defined ablation parameter E s is proved to be suitable for monitoring the excimer laser ablation processes.

Evaluation of the dimensions of growing cracks and unloading regions on the basis of acoustic signal parameters

Evaluation of the dimensions of growing cracks and unloading regions on the basis of acoustic signal parameters

Relationship between parameters of acoustic signals and dimensions of breaks in continuity during fracture of heterogeneous materials

1. By submerging a test specimen in a liquid, undesirable resonance phenomena can be eliminated, and the parameters of a single AS can be measured. 2. The AS parameters, i.e., the amplitude and duration, are closely related to the characteristic dimensions of the structural elements of heterogeneous materials. 3. The enlargement of cracks in heterogeneous materials takes place in discrete steps. The size of these steps is determined by the dimensions of the structural elements.

Spectral and source parameters of acoustic signals emitted by microcrack generation in a granite sample.

Source parameters of acoustic emission (AE) generated by crack generation in a granite sample are determined using a spectral model for the crack. To make a quantitative spectral analysis of AE possible, a relatively large sample having a size of 32×32×82cm3 is used, and a sensor consisting of a coil and a magnet is newly developed. In the spectral analysis, it is assumed that the rupture velocity amounts to 0.9Vs, where Vs is the S-wave velocity. Although no mechanism solutions of cracks are determined directly, it is deduced from the configuration of a fault zone in the sample that the mode of cracks is tensile.AE's having an amplitude that is sufficiently large for the present analysis are obtained under the ultimate stress of this experiment, which is about 60% of the compressional fracture strength of sampled rocks. Linear dimension r of cracks are estimated as 1-3cm. A quantity M0, which is defined by the rigidity multiplied by the crack volume, amounts to an order of 106-107 dyn·cm. The stress drops which are calculated from r and M0 are several bars and are relatively low compared to the tensile fracture strength of the sampled rock, which is about 170bar.

Evolution of hearing and acoustic communication in vertebrates

Selective pressures on acoustic communication fall into several general categories. (1) Reproductive isolation. The pressure for species recognition has favored both species-specific calls and sensitivity to them. In some instances, this sensitivity is accomplished by narrow tuning of the peripheral auditory system, in others apparently by higher neural mechanisms (e,g., “auditory templates”). (2) Predator avoidance. Alarm calls, for example, are often narrow-band signals which are difficult to localize. Some species may produce sounds that are inaudible to their predators; the ultrasonic vocal and hearing systems of mammals may have evolved in this context. (3) Long-distance communication between conspecifics. Animals characteristically produce calls for this purpose that are attenuated minimally over distance, and their hearing is best at frequencies near those of these calls. (4) Intraspecific contact maintainance. Contact calls, for example, are typically wide-band signals which are easily localized. (5) Complex social organization. Highly social animals have developed acoustic communication systems which require sophisticated vocal and processing mechanisms to produce and discriminate a variety of sound elements. These species show enhanced acuity for the relevant acoustic signal parameters. Some species, in addition, have increased the potential information in their vocal repertoire by using graded rather than discrete signals. There is some evidence that increases in the complexity of the vocal repertoire are accompanied by specializations of the processing mechanism, as may be true in categorical perception.