High Source Level Research Articles

A novel method to fabricate curved piezoelectric composites with high piezoelectric phase volume fraction

Underwater acoustic transducer based on high piezoelectric phase volume fraction, large thickness, large area and curved piezoelectric composites (PC) possess wider beam width, higher source level and better directivity. However, the curved PC with large size is difficult to fabricate. The preparation of curved PC with large size and high piezoelectric phase volume fraction is even more tricky. The reported methods have risks of depolarization, deformation and poor periodicity and are not suitable for preparing PC with high piezoelectric phase volume fraction and large thickness. In this work, we proposed a novel fabrication method of the shaped-mold-assisted dice and fill technology. The 1–3 PC with high piezoelectric ceramic volume fraction of 80 %, thickness of 4.3 mm and area of 340 mm × 77 mm and the 2-2 PC with high piezoelectric ceramic volume fraction of 89.5 %, thickness of 5 mm and area of 262 mm × 20 mm were fabricated. The piezoelectric coefficient d33 and relative constant stress permittivity ε33T/ε0 of 1–3 and 2-2 PCs were comparable to piezoelectric phase itself. In addition, both 1–3 and 2-2 PCs exhibited a favorable performance consistency. This method solved the problem of limited cutting depth of thin blade, realizing PC with the structure of high piezoelectric phase volume fraction (＞ 70 %) and large thickness (＞ 3 mm) and eliminates the risk of depolarization, deformation and poor periodicity. This work enabled the potential for achieving large area, high piezoelectric phase volume and special-shaped PCs, which offers new ideas for designing innovative acoustic transducers and facilitates the progress of acoustic sensing technology.

Investigating the effects of underwater noise from two vessels on the behaviour of short-finned pilot whales

Multiple whale-watching vessels may operate around cetaceans at any one time, and targeted animals may experience underwater noise effects. We hypothesised that the cumulative noise of two vessels with low source levels (SLs) will elicit lower behavioural disturbance in short-finned pilot whales (Globicephala macrorhynchus) compared to a single vessel with a higher SL. We measured the behaviour of whales during 26 controls (stationary vessel >300 m) and 44 treatments off Tenerife (Canary Islands, Spain). Treatments consisted of vessel approaches mimicking whale-watch scenarios (distance ∼60 m, speed 1.5 kn). Approaches with two simultaneous vessels, with maximum cumulative mid and low-frequency (0.2–110 kHz) weighted source levels (SLsMF-LF) 137–143 dB, did not affect mother-calf pairs’ resting, nursing, diving, respiration rate or inter-breath interval. However, a louder single vessel approach with twin petrol engines at SLsMF-LF 139–151 dB significantly decreased the proportion of time resting for the mother. The results suggest that if a single or two vessels are present, if the cumulative SL is < 143 dB, the behavioural disturbance on the whales will be negligible. By examining noise effects from multiple vessels on the behaviour of pilot whales, the importance of incorporating a noise threshold into whale-watching guidelines was emphasised.

Analysis of Nuclear Explosion Detection Capability of IMS Hydroacoustic Network

The Comprehensive Nuclear Test Ban Treaty (CTBT) organization has established a hydroacoustic network to ensure the effective detection of nuclear explosions in the vast ocean and in the atmosphere over it in order to effectively guarantee the implementation of the treaty. To assess its effectiveness, according to the reciprocity of underwater acoustic field, this study employs the hydrophone position as the central sound source and utilizes the parabolic equation, along with seabed topography and sound velocity profile data, to estimate the transmission loss. Background noise levels of station evaluation are conducted by using historical data so as to estimate the underwater nuclear explosion sound source level via a passive sonar equation. Utilizing the full ship shock trial (FSST) results of the “Ford” aircraft carrier on June 18, 2021, as a case study, the detection capability of the HA10 station for nuclear explosions is investigated. Subsequently, the network’s overall detection capability was evaluated using the source level at 20 Hz corresponding to a 1 kiloton nuclear explosion yield as a reference. Findings indicate the network’s proficiency in identifying long‐distance propagation signals, particularly those with high explosion source levels within the sound fixing and ranging (SOFAR) channel. The sensitivity analysis demonstrates the network’s ability to detect explosions smaller than 1 kg equivalent in close proximity to a station, and larger explosions exceeding 1 kg or 1 ton at greater distances. This evaluation underscores the network’s significance in detecting and monitoring underwater nuclear explosions across extensive oceanic regions.

Bio-inspired secure underwater acoustic communication strategy by shifting the natural whale whistle phase

The bio-inspired secure underwater acoustic communication strategy camouflages the information with cetacean calls, tricking the enemy into mistaking the communication signals for natural marine mammal sounds to obtain communication security, showing distinct advantages over the conventional low probability of detection secure strategies. Inspired by this, a secure underwater acoustic communication strategy by shifting the whale whistle phase is proposed. It conveys the information by modulating the phase of natural whale whistles. The killer whale is served as an example of the bio-inspired models to illustrate the proposed method due to its wide distribution and high source level. To construct high performance and well camouflaged communication sequences, the autocorrelation, cross-correlation and Doppler tolerance of the killer whale whistles are analyzed first. Then the pulse shaping and varying symbol duration strategies are designed to alleviate the spectral leakage and the cyclostationarity problem brought about by the phase shifting to further improve the communication security. Experiments have been conducted and the effectiveness and security of the proposed method are verified by the experimental results.

Variability of Echolocation Clicks in Beluga Whales (Delphinapterus leucas) Within Shallow Waters

While echolocation is vital to the sensory ecology of odontocetes, we have few data characterizing the signals of most species, limiting our understanding of key attributes of these animals, especially for those with a diverse range of habitats. Beluga whales (Delphinapterus leucas) have successfully overcome the pressures of living in both shallow and deep open water habitats. We characterized the echolocation clicks of 13 wild beluga whales during temporary capture-and-release events in Bristol Bay, Alaska (USA). We extracted and examined 556 high-quality clicks from approximately 22 hours of recordings. As a group, the duration (41.1 ± 17.3 µs; mean ± SD), peak frequency (97.9 ± 34.4 kHz), centroid frequency (101.9 ± 23.9 kHz), -3 dB bandwidth (29.1 ± 14.4 kHz), -10 dB bandwidth (67.7 ± 31.8 kHz), and root mean square (RMS) bandwidth (27.8 ± 8.1 kHz) were assessed. These are the first on-axis data from wild belugas in their natural shallow water habitat within 1 m. Beluga whales emit clicks with high frequency and high source level in extremely shallow waters regardless of the potential strong reverberations and clutter. These results provide a foundation for future studies on how this species manipulates its sonar to successfully operate in acoustically challenging shallow waters.

Underwater low frequency Helmholtz bubble resonator

Low-frequency sound sources have found application in oceanology and geoacoustic methods of remote sensing. An underwater low-frequency sound source with a pneumatically driven bubble resonator covered with an elastic membrane effectively provides a very high source level. However, it has a narrow bandwidth, and its resonant frequency is difficult to change without changing the size of the original system. Internal acoustic resonators included in a bubble filled with gas can change the frequency response of the entire source and expand its bandwidth. Internal resonant systems can be designed so that the bubble resonator can be tuned over a wide frequency range. Other systems may add one or more internal resonances and spread the emitted spectrum over a very wide frequency band. It is possible to consider various multipole resonant systems in combination with an underwater bubble. A simple and efficient system consists of a bubble resonator and an internal Helmholtz resonator. The addition of a Helmholtz resonator converts the single resonant bubble into a double resonant system and extends its bandwidth. The theory of the underwater bubble Helmholtz resonator and various applications of these resonators for practical systems are considered. The results of the experimental verification are discussed.

Detection distances in desert dwelling, high duty cycle echolocators: A test of the foraging habitat hypothesis.

High Duty Cycle (HDC) echolocating bats use high frequency echolocation pulses that are clutter resistant, but their high frequencies give them limited range. Despite their unique ability to reject background clutter while simultaneously detecting fluttering prey, the frequency of their echolocation pulses has a strong correlation with level of environmental clutter, lower frequency pulses of HDC bats being associated with more open environments. The Foraging Habitat Hypothesis (FHH) proposes that the ecological significance of these lower frequency pulses in HDC bats in open environments is that they allow longer prey detection distances. To test the FHH, we compared the frequencies, Source Levels (SLs) and detection distances of Rhinolophus capensis, a HDC bat that has been shown to vary its call frequency in relation to habitat structure. As a further test of the FHH we investigated the SLs and detection distances of Rhinolophus damarensis (a heterospecific species that occurs in the same open desert environment as R. capensis but echolocates at a higher dominant pulse frequency). In the open desert, R. capensis emitted both lower frequency and higher SL pulses giving them longer detection distances than R. capensis in the cluttered fynbos. SL contributed more to differences in detection distances in both R. capensis and R. damarensis than frequency. In a few instances, R. damarensis achieved similar detection distances to desert–inhabiting R. capensis by emitting much higher SLs despite their average SLs being lower. These results suggest that lower frequency echolocation pulses are not a prerequisite for open desert living but may increase detection distance while avoiding energetic costs required for high SLs.

Projector design for imaging of buried unexploded ordnance

Recent modeling and field experimentation has shown very-shallow-water acoustic imaging of buried unexploded ordnance (UXO) can place stringent requirements on the sonar transmit system. Achieving high-resolution imagery requires large transmit bandwidth. Imaging deeply buried UXO requires low operating frequencies and high source levels to overcome sediment attenuation. Imaging UXO near the sediment–water interface requires short transmit waveforms that require projectors with a low mechanical quality factor for accurate reproduction. This work presents the results of a recent design study, device fabrication, and acoustic testing of a new projector intended for operation as part of a buried UXO imaging system. The analysis will focus on the design and material selection of the head mass and the ring stack used in the tonpilz device. The head mass design trade considered construction from aluminum or an aluminum beryllium metal matrix composite (AlBeMet). The ring stack design trade considered traditional polycrystalline lead zirconate titanate (PZT), ternary single crystal lead indium niobium–lead indium manganese niobium titanate (PIN-PMN-PT), and textured manganese doped lead magnesium niobate–lead zirconate titanate (Mn-PMN-PZT). Finite element simulations and measured results will be presented.

Vertical sonar beam width and scanning behavior of wild belugas (Delphinapterus leucas) in West Greenland.

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 4:42 minutes of 1:04 hours of recordings. Clicks centered on the recording equipment (i.e. on-axis clicks) were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of wild belugas with an average -3 dB asymmetrical vertical beam width of 5.4°, showing a wider ventral beam. This narrow beam width is consistent with estimates from captive belugas; however, our results indicate that beluga sonar beams may not be symmetrical and may differ in wild and captive contexts. The mean apparent source level for on-axis clicks was 212 dB pp re 1 μPa and whales were shown to vertically scan the array from 120 meters distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce unwanted surface echoes from sea ice (i.e., acoustic clutter) and effectively navigate through leads in the pack ice (e.g., find breathing holes). These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).

Echolocation click parameters and biosonar behaviour of the dwarf sperm whale (Kogia sima).

Dwarf sperm whales (Kogia sima) are small toothed whales that produce narrow-band high-frequency (NBHF) echolocation clicks. Such NBHF clicks, subject to high levels of acoustic absorption, are usually produced by small, shallow-diving odontocetes, such as porpoises, in keeping with their short-range echolocation and fast click rates. Here, we sought to address the problem of how the little-studied and deep-diving Kogia can hunt with NBHF clicks in the deep sea. Specifically, we tested the hypotheses that Kogia produce NBHF clicks with longer inter-click intervals (ICIs), higher directionality and higher source levels (SLs) compared with other NBHF species. We did this by deploying an autonomous deep-water vertical hydrophone array in the Bahamas, where no other NBHF species are present, and by taking opportunistic recordings of a close-range Kogia sima in a South African harbour. Parameters from on-axis clicks (n=46) in the deep revealed very narrow-band clicks (root mean squared bandwidth, BWRMS, of 3±1 kHz), with SLs of up to 197 dB re. 1 µPa peak-to-peak (μPapp) at 1 m, and a half-power beamwidth of 8.8deg. Their ICIs (mode of 245 ms) were much longer than those of porpoises (<100 ms), suggesting an inspection range that is longer than detection ranges of single prey, perhaps to facilitate auditory streaming of a complex echo scene. On-axis clicks in the shallow harbour (n=870) had ICIs and SLs in keeping with source parameters of other NBHF cetaceans. Thus, in the deep, dwarf sperm whales use a directional, but short-range echolocation system with moderate SLs, suggesting a reliable mesopelagic prey habitat.

Do echolocating toothed whales direct their acoustic gaze on- or off-target in a static detection task?

Echolocating mammals produce directional sound beams with high source levels to improve echo-to-noise ratios and reduce clutter. Recent studies have suggested that the differential spectral gradients of such narrow beams are exploited to facilitate target localization by pointing the beam slightly off targets to maximize the precision of angular position estimates [maximizing bearing Fisher information (FI)]. Here, we test the hypothesis that echolocating toothed whales focus their acoustic gaze askew during target detection to maximize spectral cues by investigating the acoustic gaze direction of two trained delphinids (Tursiops truncatus and Pseudorca crassidens) echolocating to detect an aluminum cylinder behind a hydrophone array in a go/no-go paradigm. The animals rarely placed their beam axis directly on the target, nor within the narrow range around the off-axis angle that maximizes FI. However, the target was, for each trial, ensonified within the swath of the half-power beam width, and hence we conclude that the animals solved the detection task using a strategy that seeks to render high echo-to-noise ratios rather than maximizing bearing FI. We posit that biosonar beam adjustment and acoustic gaze strategies are likely task-dependent and that maximizing bearing FI by pointing off-axis does not improve target detection performance.

Vertical sonar beam width of wild belugas (Delphinapterus leucas) in West Greenland

Echolocation signals of wild beluga whales (Delphinapterus leucas) were recorded in 2013 using a vertical, linear 16-hydrophone array at two locations in the pack ice of Baffin Bay, West Greenland. Individual whales were localized for 12 min of 1:04 h of recordings where on-axis clicks were isolated to calculate sonar parameters. We report the first sonar beam estimate of in situ recordings of belugas with an average 3-dB asymmetrical vertical beam width of 5.7 deg, showing a wider ventral axis. This is narrower than the commonly used estimates in the literature obtained from captive whales, suggesting beluga sonar beam width may be different in captive and wild contexts and is not necessarily symmetrical. Apparent source levels ranged from 210 to 220 dB pp re 1 μPa and whales were shown to vertically scan the array from 120 m distance. Our findings support the hypothesis that highly directional sonar beams and high source levels are an evolutionary adaptation for Arctic odontocetes to reduce noise and surface echoes from ice. These results provide the first baseline beluga sonar metrics from free-ranging animals using a hydrophone array and are important for acoustic programs throughout the Arctic, particularly for acoustic classification between belugas and narwhals (Monodon monoceros).

Vessel noise levels drive behavioural responses of humpback whales with implications for whale-watching.

Disturbance from whale-watching can cause significant behavioural changes with fitness consequences for targeted whale populations. However, the sensory stimuli triggering these responses are unknown, preventing effective mitigation. Here, we test the hypothesis that vessel noise level is a driver of disturbance, using humpback whales (Megaptera novaeangliae) as a model species. We conducted controlled exposure experiments (n = 42) on resting mother-calf pairs on a resting ground off Australia, by simulating whale-watch scenarios with a research vessel (range 100 m, speed 1.5 knts) playing back vessel noise at control/low (124/148 dB), medium (160 dB) or high (172 dB) low frequency-weighted source levels (re 1 μPa RMS@1 m). Compared to control/low treatments, during high noise playbacks the mother's proportion of time resting decreased by 30%, respiration rate doubled and swim speed increased by 37%. We therefore conclude that vessel noise is an adequate driver of behavioural disturbance in whales and that regulations to mitigate the impact of whale-watching should include noise emission standards.

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

Fin whale 40‐Hz calling behavior studied with an acoustic tracking array

The sonar beam of Macrophyllum macrophyllum implies ecological adaptation under phylogenetic constraint.

All animals are adapted to their ecology within the bounds of their evolutionary heritage. Echolocating bats clearly show such adaptations and boundaries through their biosonar call design. Adaptations include not only the overall time-frequency structure, but also the shape of the emitted echolocation beam. Macrophyllum macrophyllum is unique within the phyllostomid family, being the only species to predominantly hunt for insects in the open, on or above water, and as such it presents an interesting case for comparing the impact of phylogeny and ecology as it originates from a family of low-intensity, high-directionality gleaning bats, but occupies a niche dominated by very loud and substantially less-directional bats. Here, we examined the sonar beam pattern of M. macrophyllum in the field and in a flight room and compared it to closely related species with very different feeding ecology and to that of the niche-sharing but distantly related Myotis daubentonii Our results show that M. macrophyllum uses higher source levels and emits less-directional calls than other phyllostomids. In the field, its call directionality is comparable to M. daubentonii, but in the flight room, M. macrophyllum is substantially more directional. Hence our results indicate that ecology influences the emitted call, pushing the bats to emit a louder and broader beam than other phyllostomids, but that phylogeny does limit the emitted intensity and flexibility of the overall beam pattern.

Spectral analysis using Haar wavelet (original signal, denoised signal, residual signal) and source level (SL) for whistle sound of dolphin (Tursiops aduncus) in captivity

This study discussed about Haar wavelet with a view original signal, denoised signal, and residual signal with using fourth whistle sounds of dolphin (Tursiops aduncus). The study was conducted in Safari Park, Cisarua, Bogor Indonesia with 2 dolphins. The results showed differences in results Haar wavelet, this study proves that the Haar wavelet is suitable for the analysis of dolphin sounds, and its have frequency ranged 8-22 kHz. The highest value of the noised signal was smaller than residual signal. The highest of residual signal contained in the second whistle, while the lowest was whistle 1, it showed that the larger the signal denoised result residual signal generated using Haar wavelet. The frequency of source level value ranged 8500 Hz to 11800 Hz, with the highest SL value was 43.9 dB (brown cyrcle). The lowest of the frequency of Source Level (SL) value ranged between 15700 Hz to 17990 Hz, with the lowest SL value was 38.5 dB (brown cyrcle). Whistle 1, 2, 3, and 4 have a different value SL and every SL values obtained in 1,2,3, and 4 have differences noise, it shows the same target but SL value and the sound patterns remain distinct by looking at time duration of whistle sound. Beam pattern from an omni directional sound source (DI= 0 dB, cyan trace) and a directional source following the piston model (DI= 18 dB, black trace) and beam pattern with 4 types signal have ranged value 70 º-180°, with highest intensity value was 60º.

Sperm whales reduce foraging effort during exposure to 1-2 kHz sonar and killer whale sounds.

The time and energetic costs of behavioral responses to incidental and experimental sonar exposures, as well as control stimuli, were quantified using hidden state analysis of time series of acoustic and movement data recorded by tags (DTAG) attached to 12 sperm whales (Physeter macrocephalus) using suction cups. Behavioral state transition modeling showed that tagged whales switched to a non-foraging, non-resting state during both experimental transmissions of low-frequency active sonar from an approaching vessel (LFAS; 1-2 kHz, source level 214 dB re 1 µPa m, four tag records) and playbacks of potential predator (killer whale, Orcinus orca) sounds broadcast at naturally occurring sound levels as a positive control from a drifting boat (five tag records). Time spent in foraging states and the probability of prey capture attempts were reduced during these two types of exposures with little change in overall locomotion activity, suggesting an effect on energy intake with no immediate compensation. Whales switched to the active non-foraging state over received sound pressure levels of 131-165 dB re 1 µPa during LFAS exposure. In contrast, no changes in foraging behavior were detected in response to experimental negative controls (no-sonar ship approach or noise control playback) or to experimental medium-frequency active sonar exposures (MFAS; 6-7 kHz, source level 199 re 1 µPa m, received sound pressure level [SPL] = 73-158 dB re 1 µPa). Similarly, there was no reduction in foraging effort for three whales exposed to incidental, unidentified 4.7-5.1 kHz sonar signals received at lower levels (SPL = 89-133 dB re 1 µPa). These results demonstrate that similar to predation risk, exposure to sonar can affect functional behaviors, and indicate that increased perception of risk with higher source level or lower frequency may modulate how sperm whales respond to anthropogenic sound.

Investigating the Effect of Tones and Frequency Sweeps on the Collective Behavior of Penned Herring (Clupea harengus).

We experimentally played back tones and sweeps to captive herring (Clupea harengus) in a net pen and measured the collective response of a large and a small group of fish using a camera, echo sounder, and multibeam sonar. The playbacks ranged in frequency from 160 to 500 Hz and 131 to 147 dB re 1 μPa in received sound pressure level. Herring behavior was scored by a team that blindly evaluated the observations. Overall, the responses were modest. Stronger reactions were observed at higher source levels, lower frequencies, and smaller school sizes, but there was no effect on signal rise time.

Documenting and Assessing Dolphin Calls and Ambient and Anthropogenic Noise Levels via PAM and a SPL Meter.

Song Meter SM2M marine recorders were deployed to document dolphin calls and ambient and anthropogenic noise. Recordings from Bimini were split into 2-h segments; no segment was without dolphin calls. At Dolphin Encounters, average noise levels ranged from 110 to 125 dB; the highest source level was 147.98 dB re 1 μPa at 1 m. Average ambient-noise levels documented at 4 sites in Guam were below 118 dB re 1 μPa at 1 m. These data were compared with values from a custom-built sound pressure level (SPL) meter and confirm that the SM2M recorder is a useful tool for assessing animal calls and ambient and anthropogenic noise levels.

Modeling Effectiveness of Gradual Increases in Source Level to Mitigate Effects of Sonar on Marine Mammals

Ramp-up or soft-start procedures (i.e., gradual increase in the source level) are used to mitigate the effect of sonar sound on marine mammals, although no one to date has tested whether ramp-up procedures are effective at reducing the effect of sound on marine mammals. We investigated the effectiveness of ramp-up procedures in reducing the area within which changes in hearing thresholds can occur. We modeled the level of sound killer whales (Orcinus orca) were exposed to from a generic sonar operation preceded by different ramp-up schemes. In our model, ramp-up procedures reduced the risk of killer whales receiving sounds of sufficient intensity to affect their hearing. The effectiveness of the ramp-up procedure depended strongly on the assumed response threshold and differed with ramp-up duration, although extending the duration of the ramp up beyond 5 min did not add much to its predicted mitigating effect. The main factors that limited effectiveness of ramp up in a typical antisubmarine warfare scenario were high source level, rapid moving sonar source, and long silences between consecutive sonar transmissions. Our exposure modeling approach can be used to evaluate and optimize mitigation procedures.