Whistles of beluga whales in the reproductive gathering off Solovetskii Island in the White Sea

Whistles recorded in a reproductive gathering of beluga whales near Solovetskii Island in the White Sea are analyzed. On the basis of the absolute characteristics and shape of the frequency contour, whistles are classed into 16 types. Whistles belong to a relatively low frequency band, contain many harmonics, and have a simple shape of frequency contour. The average whistle duration varies from 0.1 to 1.7 s for different types, the average value of the maximum fundamental frequency varies from 1.4 to 4.5 kHz, and the average number of inflection points is from 0 to 9 per signal. In contrast to other populations, where flat whistles are the most frequent vocalizations, beluga whales observed in the reproductive gathering in the White Sea most often produce short whistles with a V-shaped frequency contour.     

High-pitched tonal signals of beluga whales (Delphinapterus leucas) in a summer assemblage off Solovetskii Island in the White Sea

High-frequency whistles of beluga whales are analyzed. The signals are recorded in a belgua summer assemblage off Solovetskii Island in the White Sea. The high-frequency whistles are narrowband signals with a continuous waveform and a fundamental frequency above 5 kHz. On the average, they make up 7.7% of the total vocal production of the animals. Based on the shape of the fundamental frequency contour and its time-frequency parameters, the high-frequency whistles are classed into 12 types. The HF whistles have a mean fundamental frequency of 9.7 kHz, an average bandwidth of 3.3 kHz, and an average duration of 1.0 s. The number of inflection points per signal ranges from 0 to 56 with a mean of 2.3. The predominant types are flat (50%), rising (23%), and wavy (7%) high-frequency whistles. Presumably, beluga whales can use some of the whistle types for short-range communication and other types for long-range communication. Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 2, pp. 156–164. The article was translated by the authors.     

Demonstration of adaptation in beluga whale echolocation signals

The echolocation signals of the same beluga whale (Delphinapterus leucas) were measured first in San Diego Bay, and later in Kaneohe Bay, Oahu, Hawaii. The ambient noise level in Kaneohe Bay is typically 12-17 dB greater than in San Diego Bay. The whale demonstrated the adaptiveness of its biosonar by shifting to higher frequencies and intensities after it was moved to Kaneohe. In San Diego, the animal emitted echolocation signals with peak frequencies between 40 and 60 kHz, and bandwidths between 15 and 25 kHz. In Kaneohe, the whale shifted its signals approximately an octave higher in frequencies with peak frequencies between 100 and 120 kHz, and bandwidths between 20 and 40 kHz. Signal intensities measured in Kaneohe were up to 18 dB higher than in San Diego. The data collected represent the first quantitative evidence of the adaptive capability of a cetacean biosonar system.     

Characteristics of whistles from the acoustic repertoire of resident killer whales (Orcinus orca) off Vancouver Island, British Columbia

The acoustic repertoire of killer whales (Orcinus orca) consists of pulsed calls and tonal sounds, called whistles. Although previous studies gave information on whistle parameters, no study has presented a detailed quantitative characterization of whistles from wild killer whales. Thus an interpretation of possible functions of whistles in killer whale underwater communication has been impossible so far. In this study acoustic parameters of whistles from groups of individually known killer whales were measured. Observations in the field indicate that whistles are close-range signals. The majority of whistles (90%) were tones with several harmonics with the main energy concentrated in the fundamental. The remainder were tones with enhanced second or higher harmonics and tones without harmonics. Whistles had an average bandwidth of 4.5 kHz, an average dominant frequency of 8.3 kHz, and an average duration of 1.8 s. The number of frequency modulations per whistle ranged between 0 and 71. The study indicates that whistles in wild killer whales serve a different function than whistles of other delphinids. Their structure makes whistles of killer whales suitable to function as close-range motivational sounds.     

High-frequency modulated signals of killer whales (Orcinus orca) in the North Pacific

Killer whales in the North Pacific, similar to Atlantic populations, produce high-frequency modulated signals, based on acoustic recordings from ship-based hydrophone arrays and autonomous recorders at multiple locations. The median peak frequency of these signals ranged from 19.6-36.1 kHz and median duration ranged from 50-163 ms. Source levels were 185-193 dB peak-to-peak re: 1 μPa at 1 m. These uniform, repetitive, down-swept signals are similar to bat echolocation signals and possibly could have echolocation functionality. A large geographic range of occurrence suggests that different killer whale ecotypes may utilize these signals.     

Adaptive joint filtering of parameters of the pulsed signals

Based on representing parameters of the pulsed signals by discrete and continuous Markov processes, we synthesize adaptive algorithms and devices for joint nonlinear filtering of parameters of the pulsed correlated signals, whose operation does not require knowledge of a priori statistical data about the filtered process during reception. The obtained results confirm the possibility of developing the receiving devices which efficiently use the statistical redundancy of signals for improving reliability of the data transmission. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 4, pp. 364–370, April 2007.     

Passive acoustic location of bowhead whales in a population census off Point Barrow, Alaska

A sonobuoy array placed in the nearshore lead was used for locating bowhead whale sounds to determine if whales migrated past census stations beyond visual range and were uncounted. Based on a sample of 182 whale sounds (over 48 h) from closest point of approach (CPA) distances out to more than 10 km, 68% originated beyond 2 km (CPA), where only 1% of the 242 whales were sighted. No whales were sighted beyond 3 km during this time, but 53% of the located sounds originated that far and beyond. Thirty-seven other bowhead sounds over 15 h were distributed out to 6 km. Two tracked whales moved at average speeds of 1.5 and 1.8 kn. Maximum location error was 1%-25% in a sector of 120 degrees X 5-10 km, depending upon bearing and range. Most whale sounds were low-frequency moans, trumpeting roars, and repetitive sequences (songs) with peak spectrum source level up to 189 dB re: 1 microPa, 1 m. Lack of correlations between numbers of sounds and sighted whales precluded using bowhead sounds to count individuals or even to extrapolate ratios of unseen to observed whales.     

Reactions of bowhead whales, Balaena mysticetus, to seismic exploration in the Canadian Beaufort Sea

The behavioral reactions of bowhead whales to distant seismic vessels not under our control, a controlled approach by a seismic vessel, and controlled tests with a single airgun were observed. On 21 occasions in the summers of 1980-84, general activities of bowheads exposed to pulses of underwater noise (107-158 dB re: 1 mu Pa) from seismic vessels 6-99 km away were observed. Activities were indistinguishable from those without seismic noise; there was no detectable avoidance. Hints of subtle changes in surfacing, respiration, and diving behavior were unconfirmed, but were consistent with reactions to stronger noise pulses from closer seismic boats. In a test with a full-scale seismic boat (30 airguns totaling 471, source level 248 dB re: 1 mu Pa, closest point of approach = 1 1/2 km), bowheads began to orient away when the airgun array began to fire 7 1/2 km away. However, some whales continued apparent near-bottom feeding until the vessel was 3 km away. Whales were displaced by about 2 km. Reactions were not much stronger than those to any conventional vessel. Tests with one 0.66-1 airgun showed that some bowheads move away from sources of strong seismic impulses even in the absence of boat noise, and that bowheads can detect the direction from which seismic impulses arrive. In general, bowheads exhibit avoidance reactions when they receive seismic pulses stronger than about 160 dB re: 1 mu Pa. Evidence of reactions to lower received levels remains inconclusive.     

Spurious signals caused by the piezoelectric ringing of NaN02 in pulsed NMR

Spurious signals caused by the piezoelectric ringing of single crystals of NaNO₂ in pulsed NMR have been studied at 14.5 MHz using AM detection. Their amplitude is about two orders of magnitude larger than the ²³Na FID when the a axis of the crystal is along the axis of the coil, and about one order of magnitude larger than the FID when the b or c axis is along the coil axis. The buildup of the piezoelectric signals during a pulse is found to be characterized by a time constant of about 10 μec. However, the decay following the pulse is characterized by an altogether different time constant which varies with the pulse length but is of the order of 100 μsec. Measurements at different locations of the crystal relative to the rf coil show that the piezoelectric signals are generated by a wholly electrostatic interaction, primarily involving the longitudinal electric field generated by the pulse. A theoretical expression for the signal amplitude has been derived. It accounts for many properties of the signals but gives an amplitude which is two orders of magnitude larger than the experimental. Ways of suppressing the piezoelectric signals to facilitate the observation of NMR are discussed.     

The influence of the skin effect on gamma detected pulsed NMRON signals

The influence of the skin effect on single and triple (spin echo) gamma detected pulsed NMRON signals is calculated using a density matrix approach within a pure Zeeman manifold. For single pulse NMRON the turn angle dependences of the signals for uniform and exponential profiles of the resonant nuclei are presented for a typical inhomogeneous broadening applicable to intermediate mass impurities in ferromagnetic hosts. For triple pulse NMRON the baseline and principal spin echo amplitudes for equal resonant rf pulses are presented for the same inhomogeneous broadening. It is found that the skin effect leads to the form of pulsed NMRON signals that are in accord with experiment.     

On the origin of the acoustic signals generated in KDP by pulsed UV laser excitation

The origin of the acoustic signals that are generated in the bulk of a KDP crystal during irradiation with short UV laser pulses is determined. The generation of these signals by excitation with moderate or high optical fluences is linked to the evolution of the population of point defects that is generated in the crystal by absorption of two UV photons. These defects are bleached due to their efficient linear absorption of UV radiation, and their non-radiative relaxation is shown to be the origin of the acoustic signals. The rate constants for the different processes involved in both the linear and the non-linear interactions were determined from the experiments presented here. Characteristic values for the quantum efficiency for the generation of defects, _F = 0.95 ± 0.05, and for the quantum efficiency for bleaching of defects, _B = 0.065 ± 0.005, were obtained for 266-nm laser radiation. The model developed for the intensity of the acoustic signals reproduces the experimental facts with very good accuracy.     

Multiplicative-noise-induced amplification of weak signals in a system with on—off intermittency

A model of an overdamped Kramers oscillator perturbed by strong multiplicative Gaussian noise and a weak periodic signal is studied theoretically and experimentally. It is shown that under certain conditions such a system demonstrates on-off intermittency and sensitivity to very weak periodic signals, making possible many-fold (experimentally, by two orders of magnitude) amplification of the signal amplitude.     

Detecting and filtering a flow of different pulsed signals against the noise background

We consider the problem of separate detection and filtration of a flow of pulsed signals. We assume that statistically independent pulsed signals of different shape and random amplitude appear randomly against the background of noise. An algorithm for estimation of the detection probability of each signal is obtained. Recurrent expressions for thea posteriori probability density of each signal are found. The results of numerical simulation of the proposed algorithms of signal processing are presented. Lobachevsky State University of Nizhny Novgorod Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 92–100, January, 1999.     

Diversity reception of hydroacoustic signals from the results of experiments in the Black Sea

The results are presented of an experimental study of spatial and frequency correlation of amplitude fluctuations of hydroacoustic signals on two paths of the Black Sea under conditions of a thermal underwater sound channel and tonal-continuous emission at frequencies of 4 and 1.5 kHz. The emitters were located in the coastal wedge on the bottom slope at depths of 35 and 60 m; a receiver system was submerged to a depth of 50–60 m off the side of a ship drifting at various distances in the open sea. Data are presented on the spatial (horizontal and vertical) and frequency intervals of fluctuation correlation on the first path extending 100 km at an emission frequency of 4 kHz under conditions of dominant fast fluctuations, as well as on the second path extending 300 km at an omission frequency of 1.5 kHz under conditions of dominant slow fluctuations. The results of experiments are used to estimate the efficiency of space-diversity and frequency-diversity reception of acoustic signals in application to information transmission over a hydroacoustic channel.     

Mechanisms for saturation of nonlinear pulsed and periodic signals in focused acoustic beams

Acoustic fields of powerful ultrasound sources with Gaussian spatial apodization and initial excitation in the form of a periodic wave or single pulse are examined based on the numerical solution of the Khokhlov-Zabolotskaya-Kuznetsov equation. The influence of nonlinear effects on the spatial structure of focused beams, as well as on the limiting values of the acoustic field parameters is compared. It is demonstrated that pressure saturation in periodic fields is mainly due to the effect of nonlinear absorption at a shock front, while in pulsed fields is due to the effect of nonlinear refraction. The limiting attainable values for the peak positive pressure in periodic fields turned out to be higher than the analogous values in pulsed acoustic fields. The total energy in a beam of periodic waves decreases with the distance from the source faster than in the case of a pulsed field, but it becomes concentrated within much smaller spatial region in the vicinity of the focus. These special features of nonlinear effect manifestation provide an opportunity to use pulsed beams for more efficient delivery of wave energy to the focus and to use periodic beams for attaining higher values of pressure in the focal region.     

The sound speed in southern deepwater zone of the Caspian Sea,off Anzali Port

Sound velocity determination in seawater is a key component of modern hydrographic surveying; however, little data exists on sound velocity characteristics of the southern Caspian Sea. Hence, a study was undertaken in 2008 to examine the seasonal variability of sound speed in deep-waters of the South Caspian Sea near the Iranian coast. The seasonal cycle of seawater temperature and thermal stratification in the Caspian Sea water created a wide range of spatial and temporal changes of sound speed with relevant differences between shallow water (over the continental shelf) and deep-water area. The collected data showed that seasonal variations of the sound speed were most important in the upper 100 m water depth, while below this level that is in deepwater the changes were small. The maximum values of sound speed were observed at the surface in midsummer around 1517–1519 m s⁻¹ over the continental shelf while the speed of sound was about 1453 m s⁻¹ between 450–470 m depths with no major seasonal variations. Variations in vertical structure of the sound speed were in agreement with temperature changes, while effects of the salinity on the sound speed were little.     

Spatial correlation of explosion-generated signals received by longitudinally separated hydrophones in the Mediterranean Sea

Results of an experiment carried out in the Mediterranean Sea on a propagation track ～400 km in length are presented. The sources of sound were 2.5-kg trinitrotoluene charges. The signals were received by three hydrophones spatially separated along the track by distances of 100 and 300 m. The hydrophones were carried by radio buoys, which were connected with each other and with the receiving vessel. The frequency band under study was 240–340 Hz. Under the conditions of the experiment, the spatial correlation interval obtained with averaging over the spreading time of multipath signals proved to be smaller than 100 m. It was shown that the resolution of signals arriving over individual ray paths or in narrow ray bundles considerably increased this interval. In this case, its experimental value was found to exceed 300 m.