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Fish biomass and stock assessment are estimated from acoustic volume backscattering strengths (Sv) obtained from various hydroacoustic equipment. Although sound attenuation due to fish schools and water influences the Sv value, only attenuation from water is considered during the acoustic data process. For these reasons, it is necessary to understand the characteristics of sound attenuation by fish. Unfortunately, little is known about sound attenuation from fish. In the present study, the attenuation from one to four fish specimens was precisely measured during ex situ experiments in a water tank. The scientific echo sounder of a split-beam 200 kHz transducer and a miniature hydrophone were used for the attenuation measurements. Results show that the maximum attenuation coefficient (α) was approximately 25 dB/cm when the 4 multiple fishes had high fish heights. The relationship between the attenuation coefficient ( α 200 k H z ) and the total fish height ( H t o t a l ) was approximately α 200 k H z = 0.54 ∗ H t o t a l   ±   0.06   ( r 2 = 0.72 ). This work describes the sound attenuation characteristics to provide basic information for the compensation of Sv from fish schools or layers. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to solve the problem that strong noise interference seriously affects the direction of arrival (DOA) estimation in complex underwater acoustic environment. In this paper, a combined noise reduction algorithm and micro-electro-mechanical system (MEMS) vector hydrophone DOA estimation algorithm based on singular value decomposition (SVD), variational mode decomposition (VMD) and wavelet threshold denoising (WTD) is proposed. Design/methodology/approach: Firstly, the parameters of VMD are determined by SVD, and the VMD method can decompose the signal into multiple intrinsic mode functions (IMFs). Secondly, the effective IMF component is determined according to the correlation coefficient criterion and the IMF less than the threshold is processed by WTD. Then, reconstruction is carried out to achieve the purpose of denoising and calibration baseline drift. Finally, DOA estimation is achieved by the combined directional algorithm of preprocessed signal. Findings: Simulation and field experiments results show that the algorithm has good noise reduction and baseline drift correction effects for nonstationary underwater signals, and high-precision azimuth estimation is realized. Originality/value: This research provides the basis for MEMS hydrophone detection and positioning and has great engineering significance in underwater detection system. [ABSTRACT FROM AUTHOR]

Performing reproducible vessel source level (SL) measurements is complicated by seabed reflections in shallow water. In deep water, with a hydrophone far from the seabed, it is straightforward to estimate propagation loss (PL) and convert sound pressure level (SPL) into SL using the method codified in the international standard ISO 17208-2 [International Organization for Standardization (ISO), Geneva, Switzerland (2019)]. Estimating PL is more difficult in shallow water because of the way that sound reflects from the seabed such that multiple propagation paths contribute to SPL. Obtaining reproducible SL measurements in shallow water requires straightforward and robust methods to estimate PL. From May to July 2021, a field experiment evaluated different methods of measuring vessel SL in shallow water. The same vessels were measured many times in water depths of 30, 70, and 180 m. In total, 12 079 SL measurements were obtained from 1880 vessel transits and 16 hydrophones, distributed across 3 moored vertical line arrays and 2 moored horizontal line arrays. The experiment confirmed that it is possible to obtain reproducible vessel SL estimates in shallow water comparable to within ±2.5 dB of ISO-compliant measurements in deep water and repeatable to within ±1.5 dB. [ABSTRACT FROM AUTHOR]

The article considers the problem that arises during the amplitude-phase calibration of hydrophones by the reciprocity method and consists in the violation of the consistency of the hydrophone characteristics specified by the manufacturer. Violation of the indicated consistency of characteristics is due to the need to determine the phase-frequency characteristic when calibrating the hydrophone. The manufacturer sets the dimensions of the hydrophone receiving part and the position of the acoustic center according to the drawing of the receiving part and thereby replaces the acoustic parameters with geometric ones. To restore the consistency of the characteristics, it is proposed to determine the position of the acoustic center and the equivalent size of the hydrophone receiving part from the results of acoustic measurements. It is shown that the displacement of the hydrophone acoustic center relative to its geometric center is a typical phenomenon, and the geometric and acoustically measured dimensions of the active element can differ. To ensure the unity of acoustic measurements, it is proposed to introduce the concept of an equivalent radius and to clarify the concept of the hydrophone acoustic center, as well as to standardize the methods of their experimental determining. The results obtained will be useful in monitoring the phase responses of elements of hydroacoustic antennas for various purposes, ensuring the identity of the phase-frequency characteristics of the vector receivers measuring channels, in solving problems related to restoring the acoustic signal shape by the recorded voltage at the receiver output and other various applications, including marine ecology, medical ultrasound studies, etc. [ABSTRACT FROM AUTHOR]

The Kuiyang-ST2000 deep-towed high-resolution multichannel seismic system was designed by the First Institute of Oceanography, Ministry of Natural Resources (FIO, MNR). The system is mainly composed of a plasma spark source (source level: 216 dB, main frequency: 750 Hz, frequency bandwidth: 150–1 200 Hz) and a towed hydrophone streamer with 48 channels. Because the source and the towed hydrophone streamer are constantly moving according to the towing configuration, the accurate positioning of the towing hydrophone array and the moveout correction of deep-towed multichannel seismic data processing before imaging are challenging. Initially, according to the characteristics of the system and the towing streamer shape in deep water, travel-time positioning method was used to construct the hydrophone streamer shape, and the results were corrected by using the polynomial curve fitting method. Then, a new data-processing workflow for Kuiyang-ST2000 system data was introduced, mainly including float datum setting, residual static correction, phase-based moveout correction, which allows the imaging algorithms of conventional marine seismic data processing to extend to deep-towed seismic data. We successfully applied the Kuiyang-ST2000 system and methodology of data processing to a gas hydrate survey of the Qiongdongnan and Shenhu areas in the South China Sea, and the results show that the profile has very high vertical and lateral resolutions (0.5 m and 8 m, respectively), which can provide full and accurate details of gas hydrate-related and geohazard sedimentary and structural features in the South China Sea. [ABSTRACT FROM AUTHOR]

The acoustic method, which enables continuous monitoring with great temporal resolution, is an alternative technique for detecting bedload movement. In order to record the sound signals produced by the impacts between gravel particles and detect the bedload motion, in this study, a hydrophone is placed close to the riverbed at the upper Yangtze River. Three categories of raw audio signals—moving gravel particles, ship engines, and flow turbulence—are collected and investigated. Signal preprocessing is performed using spectral subtraction to reduce the noise of the background sound, and the sound signal characteristic parameters are then calculated. In this paper, we propose a novel method for detecting and extracting bedload motion parameters, including peak frequency, pitch frequency, and energy eigenvector. When a segment of a speech signal meets the indicators for all three feature parameters simultaneously, the segment signal is classified as a bedload motion sound signal. Further work will be conducted to investigate bedload transport using the extracted audio signal. [ABSTRACT FROM AUTHOR]

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In this work, a miniaturized, low-cost, low-power and high-sensitivity AlN-based micro-electro-mechanical system (MEMS) hydrophone is proposed for monitoring water pipeline leaks. The proposed MEMS Hydrophone consists of a piezoelectric micromachined ultrasonic transducer (PMUT) array, an acoustic matching layer and a pre-amplifier amplifier circuit. The array has 4 (2 × 2) PMUT elements with a first-order resonant frequency of 41.58 kHz. Due to impedance matching of the acoustic matching layer and the 40 dB gain of the pre-amplifier amplifier circuit, the packaged MEMS Hydrophone has a high sound pressure sensitivity of −170 ± 2 dB (re: 1 V/μPa). The performance with respect to detecting pipeline leaks and locating leak points is demonstrated on a 31 m stainless leaking pipeline platform. The standard deviation (STD) of the hydroacoustic signal and Monitoring Index Efficiency (MIE) are extracted as features of the pipeline leak. A random forest model is trained for accurately classifying the leak and no-leak cases using the above features, and the accuracy of the model is about 97.69%. The cross-correlation method is used to locate the leak point, and the localization relative error is about 10.84% for a small leak of 12 L/min. [ABSTRACT FROM AUTHOR]

Porous piezoelectric materials have been widely used in hydrophone applications owing to their excellent hydrostatic charge constant (dh) and voltage constant (gh). However, owing to the difficulty in sample manufacturing, the evaluation of the overall piezoelectric properties for reliable device design using simulations is challenging. Herein, a two-step simulation was performed to accurately determine the overall properties of the porous PZT. First, the piezoelectric charge constant was calculated by displacement calculations using the electrostrictive effect. Second, using the calculated piezoelectric charge constant and impedance spectrum obtained from the experiment, the initial value for optimizing the properties was selected, and the overall properties were obtained using the parametric estimation technique. These parametric estimation simulation procedures were performed with the samples of radial and thickness modes based on the IEEE standards. Finally, the piezoelectric properties obtained were compared and verified with the experimental values. Therefore, the overall piezoelectric properties include mechanical, frequency and dielectric properties according to the porosity were obtained with reliable results. [ABSTRACT FROM AUTHOR]

The long propagation delay of acoustic links leads to the complex randomness of packet collision, which reduces the network packet delivery rate (PDR) and aggravates network congestion. A single vector hydrophone with directional reception characteristics can concentrate the reception gain on a certain direction, which can increase spatial reuse, reduce packet collision, and help to improve the performance of the underwater acoustic wireless sensor networks (UASNs). Herein, this paper proposes a cross-layer protocol with low interference and low congestion (CLIC) based on directional reception. An integrated routing-medium access control (MAC) design is also devised in the CLIC scheme to use the directional beams to create the least-interfering, highest-capacity data transmission links, weighing key factors affecting network performance to obtain routes with low collisions and low congestion. Simulation results show that the CLIC has a higher packet delivery rate (PDR) and higher energy efficiency compared to the QELAR, CITP, and VBF protocols. [ABSTRACT FROM AUTHOR]

The Tamu Massif, considered the biggest single volcano on Earth, was formed by the accumulation of enormous amounts of magma erupting to the surface. It is the largest and oldest seamount in Shatsky Rise, which is the third largest oceanic plateau on Earth. However, the formation mechanism of Tamu Massif is still controversial because evidence point to different formation hypotheses. In this paper, we applied the P-wave coda autocorrelation method and used the hydrophone waveform data acquired by the ocean bottom seismometer (OBS) deployed on Tamu Massif to constrain the oceanic crust, and these results provide new finding on the structure of the oceanic crust for Tamu Massif. We hope it can provide some implications to research the formation mechanism of Tamu Massif. These results show that some stations in Tamu Massif received reflection signals from shallower depths that are nearly parallel to the seafloor. We infer that in the shallow oceanic crust, there is a layer composed of alternating eruptions of dense, higher velocity massive lava and sparse, lower velocity pillow lava flows, which have less density and lower velocity compared to the lower oceanic crust, with a strong acoustic impedance contrasts between them and thus able to generate a reflection signal, which is observed in our autocorrelation results.

Abstract Passive acoustic monitoring (PAM) involves recording the sounds of animals and environments for research and conservation. PAM is used in a range of contexts across terrestrial, marine and freshwater environments. However, financial constraints limit applications within aquatic environments; these costs include the high cost of submersible acoustic recorders. We quantify this financial constraint using a systematic literature review of all ecoacoustic studies published in 2020, demonstrating that commercially available autonomous underwater recording units are, on average, five times more expensive than their terrestrial equivalents. This pattern is more extreme at the low end of the price range; the cheapest available aquatic autonomous units are over 40 times more expensive than their terrestrial counterparts. Following this, we test a prototype low‐cost, low‐specification aquatic recorder called the ‘HydroMoth’: this device is a modified version of a widely used terrestrial recorder (AudioMoth), altered to include a waterproof case and customisable gain settings suitable for a range of aquatic applications. We test the performance of the HydroMoth in both aquaria and field conditions, recording artificial and natural sounds, and comparing outputs with identical recordings taken with commercially available hydrophones. Although the signal‐to‐noise ratio and the recording quality of HydroMoths are lower than commercially available hydrophones, the recordings with HydroMoths still allow for the identification of different fish and marine mammal species, as well as the calculation of ecoacoustic indices for ecosystem monitoring. Finally, we outline the potential applications of low‐cost, low‐specification underwater sound recorders for bioacoustic studies, discuss their likely limitations, and present important considerations of which users should be aware. Several performance limitations and a lack of professional technical support mean that low‐cost devices cannot meet the requirements of all PAM applications. Despite these limitations, however, HydroMoth facilitates underwater recording at a fraction of the price of existing hydrophones, creating exciting potential for diverse involvement in aquatic bioacoustics worldwide.

The real-time monitoring of spectral characteristics of microbubble (MB) acoustic emissions permits the prediction of increases in blood–brain barrier (BBB) permeability and of tissue damage in MB-mediated focused ultrasound (FUS) brain therapy. Single-element passive cavitation detectors provide limited spatial information regarding MB activity, greatly affecting the performance of acoustic control. However, an array of receivers can be used to spatially map cavitation events and thus improve treatment control. The spectral content of the acoustic emissions provides additional information that can be correlated with the bio-effects, and wideband receivers can thus provide the most complete spectral information. Here, we develop a miniature polyvinylidene fluoride (PVDF thickness = 110 μm, active area = 1.2 mm2) broadband receiver for the acoustic monitoring of MBs. The receiver has superior sensitivity (2.36–3.87 V/MPa) to those of a commercial fibre-optic hydrophone in the low megahertz frequency range (0.51–5.4 MHz). The receiver also has a wide −6 dB acceptance angle (54 degrees at 1.1 MHz and 13 degrees at 5.4 MHz) and the ability to detect subharmonic and higher harmonic MB emissions in phantoms. The overall acoustic performance of this low-cost receiver indicates its suitability for the eventual use within an array for MB monitoring and mapping in preclinical studies. [ABSTRACT FROM AUTHOR]

Improving the line-spectrum detection capability of a single hydrophone is of great significance for the passive detection of small underwater platforms. In this paper, we propose a single-hydrophone cross-power spectrum (SHCS) method based on time-domain coherence. This method uses the coherence of the line spectrum and the non-coherence of the continuous spectrum noise to obtain coherent gain and improve the signal-to-noise ratio (SNR) of the line spectrum. The effects of the input SNR, number of averaging operations, and overlap ratio on the performance of the SHCS method under a background of Gaussian white noise are simulated and analyzed. The results show that when the overlap ratio is 0 and the number of averaging operations reaches saturation, the SHCS method can achieve the best performance and about 15 dB coherence gain is obtained. The performance of the SHCS method was verified by sea experiments. Under the extremely low input SNR, in which the line spectrum was almost completely submerged in the marine environmental noise, the SHCS method can obtain about 10 dB coherence gain. Under the conventional input SNR, in which the line spectrum could be observed, the SHCS method can obtain about 13 dB coherence gain. The results of processing the radiated noise from an actual cargo ship also demonstrate the effectiveness of the SHCS method. [ABSTRACT FROM AUTHOR]

The low-frequency impulsive gunshot vocalizations of baleen whales exhibit dispersive propagation in shallow-water channels which is well-modeled by normal mode theory. Typically, underwater acoustic source range estimation requires multiple time-synchronized hydrophone arrays which can be difficult and expensive to achieve. However, single-hydrophone modal dispersion has been used to range baleen whale vocalizations and estimate shallow-water geoacoustic properties. Although convenient when compared to sensor arrays, these algorithms require preliminary signal detection and human labor to estimate the modal dispersion. In this paper, we apply a temporal convolutional network (TCN) to spectrograms from single-hydrophone acoustic data for simultaneous gunshot detection and ranging. The TCN learns ranging and detection jointly using gunshots simulated across multiple environments and ranges along with experimental noise. The synthetic data are informed by only the water column depth, sound speed, and density of the experimental environment, while other parameters span empirically observed bounds. The method is experimentally verified on North Pacific right whale gunshot data collected in the Bering Sea. To do so, 50 dispersive gunshots were manually ranged using the state-of-the-art time-warping inversion method. The TCN detected these gunshots among 50 noise-only examples with high precision and estimated ranges which closely matched those of the physics-based approach. [ABSTRACT FROM AUTHOR]

Various approaches to the formulation of the definition of an acoustic center of a transducer and the problems arising when using them for experimental determination of the acoustic-center position are considered. The reasons for which the formulation and the corresponding method for determining the position of the acoustic center of a microphone are not suitable for a hydrophone are discussed. An experiment is described that demonstrates the proposed method for experimentally determining the position of the acoustic center of a hydrophone during its phase calibration by the reciprocity method. [ABSTRACT FROM AUTHOR]

Improving the stability of underwater LIBS is a key point for its practical use in oceanic applications. The traditional normalization method of using the internal standard element is often limited in some practical cases due to the lack of a suitable element as a reference. In this study, we compared three external normalization strategies by using plasma acoustic signals, plasma images, and the acoustic-image combination. The acoustic signals were measured with two types of hydrophone (needle hydrophone and spherical hydrophone), and the plasma images were recorded with a low-cost CCD camera. The characteristics of the acoustic signals were studied first, and the correlations of the acoustic intensities and image intensities with the LIBS spectral intensities were analyzed. Then, three normalization models were established respectively based on the acoustic data, image data, and acoustic-image combined data using the partial least squares regression (PLSR). It shows that acoustic normalization has a comparable performance on the reduction of spectral fluctuation versus image normalization, while the acoustic-image combined normalization works more efficiently than using the acoustic or image normalization only. Calibration curves of Mn, Sr, and Li were also built with the three normalization methods, and the obtained results demonstrated the availability of applying plasma acoustic signals and plasma images in improving the analytical performances of underwater LIBS. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF) has been a kind of particularly attractive piezoelectric materials for its excellent piezoelectric property. Due to its light weight, impedance characteristic is very similar to water, and good mechanical flexibility, PVDF piezoelectric film is very suitable for the field of hydrophones. Although the piezoelectric ceramic hydrophone has been widely used, but due to the disadvantage of high inherent frequency and fragile characteristics of the piezoelectric ceramics slice, the development of the piezoelectric hydrophone is limited. The application of PVDF piezoelectric film has solved many problems encountered in the use of piezoelectric ceramics. In this article, the classification of hydrophone is briefly introduced at first, and then the current status of hydrophone research is involved. And then, by analyzing the electrical equivalent model of the PVDF piezoelectric sensitive unit, the signal conditioning circuit of the PVDF piezoelectric hydrophone is summarized as well. After that, the current status of PVDF hydrophone research is discussed. Finally, a summary of all the work listed in this article is given and an outlook of PVDF hydrophone is proposed. [ABSTRACT FROM AUTHOR]

Featured Application: Resource and environmental effects of coastal region and background noise. The continuous data from the YL array and four AU stations during the lifetime of the cyclone TOMAS in March 2010 were downloaded from IRIS. By performing frequency-wave number (F-K) analysis on the array data, it was found that the orientation of the maximum energy of the secondary microseisms (0.1~0.5 Hz) was consistent with the movement of TOMAS when the central wind speed reached the typhoon level. The high wind speed of the cyclone could generate secondary microseisms as well as the high swell. However, the large global earthquake can affect the microseismic observations using F-K. The AU stations have a better microseism observation than the YL array, which might be due to the vibrating and tilting of the hydrophone caused by the turbulence. The F-K analysis on microseisms can produce better slowness and back azimuth observations than polarization. [ABSTRACT FROM AUTHOR]

Sonosensitive perfluorocarbon F8TAC18-PFOB emulsion is under development to enhance heating, increase thermal contrast, and reduce treatment times during focused ultrasound tumor ablation of highly perfused tissue. The emulsion previously showed enhanced heating during ex vivo and in vitro studies. Experiments were designed to observe the response in additional scenarios by varying focused ultrasound conditions, emulsion concentrations, and surfactants. Most notably, changes in acoustic absorption were assessed with MR-ARFI. Phantoms were developed to have thermal, elastic, and relaxometry properties similar to those of ex vivo pig tissue. The phantoms were embedded with varying amounts of F8TAC18-PFOB emulsion or lecithin-PFOB emulsion, between about 0.0-0.3% v:w, in 0.05% v:w increments. MR-ARFI measurements were performed using a FLASH-ARFI-MRT sequence to obtain simultaneous displacement and temperature measurements. A Fabry-Perot hydrophone was utilized to observe the acoustic emissions. Susceptibility-weighted imaging and relaxometry mapping were performed to observe concentration-dependent effects. 19F diffusion-ordered spectroscopy NMR was used to measure the diffusion coefficient of perfluorocarbon droplets in a water emulsion. Increased displacement and temperature were observed with higher emulsion concentration. In semi-rigid MR-ARFI phantoms, a linear response was observed with low-duty cycle MR-ARFI sonications and a mono-exponential saturating response was observed with sustained sonications. The emulsifiers did not have a significant effect on acoustic absorption in semi-rigid gels. Stable cavitation might also contribute to enhanced heating. [ABSTRACT FROM AUTHOR]

Methods for increasing the accuracy of hydrophone phase calibration are considered. It is shown that when calibrating a hydrophone, the reference center, for example, the geometric center of the contour of the active element of the hydrophone, can be displaced relative to the acoustic center of the active element due to the uneven thickness of the waterproofing coating of the element. A method is proposed for determining the position of the acoustic center of a hydrophone relative to a selected reference center. The scheme of the experiment to determine the position (displacement) of the acoustic center of a hydrophone relative to the geometric center of the contour of the active element is described. The results of experiments for different types of hydrophones are presented and the sources of measurement uncertainty are analyzed. It is shown that taking into account the displacement of the acoustic center makes it possible to improve the accuracy of the phase calibration of hydrophones. The proposed method can be used in the field of hydroacoustic measurements of the sensitivity of sound pressure receivers. [ABSTRACT FROM AUTHOR]

Automated detection and classification of the vocalizations of North Atlantic right whale (NARW) and other marine mammals is a highly desirable goal for researchers and managers seeking to monitor areas for whale presence as the basis to implement mitigation measures. Such automated acoustic processing is particularly important for real-time monitoring approaches where there are large-scale acoustic data inputs. All of the Detection and Classification Systems (DCSs) used by Fisheries and Oceans Canada (DFO) are expected to perform similarly well, given the metric (e.g., hours with calls/day) used to present NARW occurrence time-series. Previously, this was demonstrated by comparing performances of a variety of detectors during studies in 2004, 2013, and 2017. Spectroplotter (a commercial programme) and Low-Frequency Detection and Classification System (LFDCS), which are the two systems that have been used to analyse acoustic data in Newfoundland and Labrador (NL) and Maritimes regions, perform well; although in one small study the LFDCS detected more actual NARW upcalls than Spectroplotter, but also generated more false positives. DCS performance is influenced by multiple factors, including the ambient noise levels relative to the characteristics of the NARW upcalls, the location of the hydrophone, the characteristics of the recorder instrumentation, software settings and thresholds, and other contextual features, such as the presence of other species. The next generation of DCSs will incorporate context into their logic (e.g., presence of other marine mammals or abiotic sound sources and signal-to-noise ratio [SNR]). Algorithm comparisons are less crucial in the historic NARW analyses as the metrics in which the present detection results are presented at a large enough scale ("has there been NARW detected at this recorder location today?") that slight differences in algorithm performance would be subsumed in the amalgamation and summation process. At smaller spatial and temporal sampling scales, differences in algorithm performance become more apparent. Thorough testing of the different DCSs being used in Atlantic Canada would require a series of manually validated acoustic datasets from a representative set of locations, time frames, seasons, and recording hardware. Such a DCS comparison would be a useful activity but would require agreed upon performance metrices and thresholds for the DCS. [ABSTRACT FROM AUTHOR]

The pressure measurement using a fiber optic prove hydrophone and simultaneous two-directional observation with a high-speed video camera have been conducted to investigate the collapse of a laser-induced bubble near a rigid wall and the corresponding Shockwave generation. Pressure measurements at multiple locations near the rigid wall and observations of frontal and overhead views relate to the locations of pitting damage due to bubble collapse observed by Philipp and Lauterborn (J. Fluid Mech., 1998). In y=s/Rmax ≅ 1.5 where s is the distance between the bubble center and the wall surface and Rmax is the equivalent bubble radius at the maximum growth, the second bubble collapse occurs on the rigid wall: the overhead view reveals that the bubble collapses asymmetrically with a toroidal (ring) shape and bubble blobs remain at the bubble center and on both sides of the ring in the direction of laser injection. It is shown that the area of the bubble blobs on the ring correlates with the high pressure on the wall. This suggests that the collapse of these blobs leads to the high pressures and asymmetric pitting damages on the wall. [ABSTRACT FROM AUTHOR]

The diving behavior of this group of 12 Baird's beaked whales aligns with what is known about this species and beaked whales in general. Little is known about the foraging depths of Baird's beaked whales ( I Berardius bairdii i ). Diving behaviour of a Baird's beaked whale, Berardius bairdii, in the slope water region of the western North Pacific: first dive records using a data logger. [Extracted from the article]

Patterns of underwater human-generated noise events and durations of noise-free intervals (NFIs) are soundscape metrics that can potentially affect animal communication and behavior. Due to the arduous task of manual analysis, these metrics have not been described in Glacier Bay National Park and Preserve (GBNP). To surmount this challenge, we created a machine-learning (ML) model trained on 18 hr of labeled audio samples from a hydrophone operating in GBNP since 2000. The validated convolutional neural net transfer-learning model (GBNP-CNN) was used to classify several categories of sound sources in nearly 9,000 hours of data from the same hydrophone, enabling our study of vessel noise between 2017 and 2020. We focused on the occurrence and duration of NFI and the hourly proportion (HP) of vessel noise. As expected, shorter NFI and higher HP were found during daytime hours. The GBNP-CNN F1 score was 75%, largely due to the model’s confusion of vessel noise with harbor seal roars. Therefore, NFI lengths should be considered minimum estimates, but the errors do not qualitatively affect diurnal or seasonal patterns. In 2018, mean daytime NFI during peak tourism months (June–August) was less than half the duration compared to May and September (1.3 min vs. 2.9 min). In 2020, when large-vessel tourism was substantially reduced but small-craft activity continued, we found that HP decreased in June–August. In conjunction with other soundscape metrics, monitoring NFI trends using ML models such as GBNP-CNN will provide crucial information for management and conservation of acoustic habitats and sensitive species in GBNP. [ABSTRACT FROM AUTHOR]

A vector hydrophone is an underwater acoustic sensor that can detect the direction of a sound source. Wide-band characteristics and high sensitivity enhance the performance of underwater surveillance systems in complex environments. A vector hydrophone comprising a triaxial piezoelectric accelerometer and spherical hydrophone was fabricated and tested in the air and underwater. The vector hydrophone was designed to exceed the quantitative figures of merit (i.e., receiving voltage sensitivity and bandwidth) of commercially available hydrophones. Accelerometer performance was enhanced by placing a pair of piezoelectric single crystals on each axis and modifying the seismic mass material. The receiving voltage sensitivity of the omnidirectional hydrophone was approximately −160 dB relative to 1   V / μ Pa with the amplifier in water; the sensitivity of the accelerometer exceeded 300 mV/g in air and −215 dB relative to 1   V / μ Pa underwater over the frequency range of interest. The receiving directivity of the vector hydrophone was validated underwater, which confirmed that it could detect the direction of a sound source. [ABSTRACT FROM AUTHOR]

The two-stage suspension system (TSSS) is designed for the fiber optic vector hydrophone (FOVH) to isolate the vibration from the mooring rope. The acceleration transmissibility of the TSSS is studied theoretically and experimentally. The results show that the TSSS has a major advantage over the traditional one-stage suspension system (OSSS). Typically, the vibration isolation of the TSSS is demonstrated to be over 25 dB higher than that of the OSSS at 100 Hz. Meanwhile, it is demonstrated that the TSSS has little negative influence on the in-band acceleration response of the FOVH. The TSSS has the prospect of reducing the mechanical noise of the FOVH, which is conducive to suppressing the self-noise and enhancing the ability of weak signal detection. [ABSTRACT FROM AUTHOR]

This paper studies resolution of matched field processing for locating, in range and depth, a broadband underwater acoustic source from data measured at a single hydrophone receiver. For the case of an ideal rigid shallow-water waveguide with a pressure-release top boundary and a rigid bottom boundary, the paper derives approximations for the main-lobe widths of the ambiguity surface. The two cases studied in this paper are (1) when coherent measurements of the pressure are available, with the transmitted source waveform precisely known, and (2) when only measurements of the received-signal pressure magnitude-squared are available, such as might occur when the transmitted signal is random and unknown. The analysis uses the normal-mode expansion for the pressure field to derive approximate expressions for the ambiguity-surface main-lobe widths, as a function of the number of modes and frequency band, for both range and depth. Numerical results are presented corroborating the analytical analysis. Finally, the paper argues that this ambiguity analysis can also give insights into Pekeris waveguides under appropriate conditions and shows numerical simulations of matched-field localization ambiguity surfaces for some realistic shallow-water Pekeris environments. [ABSTRACT FROM AUTHOR]

This study presents the complete, detailed development process of an enhanced one-man portable Lagrangian float designed for littoral deployment to depths of up to 300 m. The design focused on maximization of the Lagrangian characteristics of the hull, minimization of the noise emission and energy efficiency of the propulsion system, and the versatility of the platform for various scientific missions. The platform is propelled by a variable buoyancy engine that is actuated by an oil-submerged, gas-pressure assisted micro gear pump. The pressure assistance lowers the pressure differential across the pump ports at depth, resulting in quieter and more efficient operation. An enhanced proportional–integral–differential control scheme is employed to pilot the platform. To enhance diving safety, a software safety agent was incorporated. If the software safety agent detects a major failure, a drop weight is released. To eliminate the chance of water ingress through dynamic hull penetration, the drop weight is actuated by an in-house developed magnetic coupling mechanism. An onboard installed hydrophone continuously records and monitors ambient sounds for phenomena of interest and enables commands and mission updates from the surface. For surface recovery, the platform is equipped with GPS and an Iridium beacon for long-range localization, and an RF beacon and strobe for short-range localization and as a backup. The performance of the platform is demonstrated in a simulation and in an actual real sea mission conducted in the eastern Mediterranean at a depth of 10 and 12 m. [ABSTRACT FROM AUTHOR]

As the core equipment of Underwater acoustic detection, MEMS vector hydrophones are applied to Unmanned Underwater Vehicles (UUV), which can better detect underwater targets. Most of the MEMS vector hydrophones currently used are long-tube cylindrical, relatively large in volume and weight, which is not suitable for installation on UUV. The co-vibration vector hydrophone is small in size and weight, but it needs elastic suspension due to the requirements of the working principle. Therefore, according to the needs of practical engineering applications, this paper designs an Embedded UUV Conformal MEMS Vector Hydrophone (ECVH), establishes an encapsulation model through theoretical analysis, and uses COMSOL6.0 to simulate its acoustic performance. The sensitivity and directionality of the ECVH are verified in the standing wave barrel. When the test frequency is 630 Hz, the sensitivity of the vector channel is −182.3 dB, and the depth of the ' 8 ' direction concave point is greater than 35 dB. The sensitivity of the sound pressure channel is −182 dB, which is omnidirectional. Finally, it is mounted on UUV for preliminary signal acquisition verification test. The test results show that the ECVH can work normally on UUV, which provides a new idea for underwater small platform test. [Display omitted] • An embedded MEMS vector hydrophone conformal with UUV is designed according to the needs of practical application engineering. • The embedded MEMS vector hydrophone is small in size, light in weight and can be rigidly fixed. • The embedded MEMS vector hydrophone has good directivity, and the vector channel is consistent with the sound pressure channel. [ABSTRACT FROM AUTHOR]

• Air bubbles of 2.24 to 1.43 mm radii in a quiescent liquid are generated in laboratory. • A smoothed horizontal edge syringe tube and 97 degrees-rotated metallic sharp needles are the injectors. • Acoustical signals were recorded with a condenser microphone (PTFE-Electret) adapted as a hydrophone. • Physical-hydrodynamic events such as a beat phenomenon is observed as bubble shape changes. • Theoretical curve fits to bubble sound emissions is a promising tool to confirm the presence of beats. Understanding the passive acoustic signals of gas bubbles has become increasingly imporant due to their growing relevance in ambient marine acoustics and medical areas, as well as the recent search for dark matter by Bubble Chamber Detectors. Here the acoustic signatures of 2.24, 1.83, 1.75, 1.66 and 1.43 mm radii bubbles are reported experimentaly. They were generated by two different air injectors in a quiescent liquid, a standard plastic syringe tube and 97 degrees-rotated metallic needles. The evolution of the sound pulse over time is presented alongside simultaneous images of the bubbles detaching from the injector and moving freely in the liquid. The beat-wave phenomenon is the standard interference pattern between two sounds of slightly different frequencies, generating a beat-period envelope of "rosary chain" form. In this study, beats are observed when the bubble exhibits changes in its shape through Cassini-oval, trapezoid, 'guitar pick', ellipsoid and oblate shapes, which is in agreement with earlier results on bubble fragmentation in a locally sheared flow. Finally, theoretical curve fits of freely-oscillating, lightly-damped bubble sound emissions confirm that the beats are due to changes in the bubble shapes. [ABSTRACT FROM AUTHOR]

Dolphins produce narrowband and frequency modulated sounds called whistles during a variety of behavioral contexts. Dolphin species vary in their whistle contour composition, frequency range, modulation, and duration, and these differences can be useful in their identification. Here, we compare the whistle contours of two sympatric dolphin species at La Paz Bay, Gulf of California, the Eastern Tropical Pacific bottlenose dolphin, and the long-beaked common dolphin. Dolphins were recorded (7 h and 1 min recording effort) from the research vessel with the engine off using an over-the-side hydrophone and a broadband recording system. A total of 666 high quality whistles (bottlenose dolphin, n = 415; long-beaked common dolphin, n = 251) were analyzed. A Random Forest Analysis identified duration, ending frequency, and maximum frequency as the most important variables that distinguish the two dolphin species. The most common whistle contour types of bottlenose dolphins were sine and convex, while the long-beaked common dolphins produced mainly upsweep and concave whistles. The results showed that bottlenose dolphins and long-beaked common dolphins differ in their whistle variables and contours facilitating their identification in future passive acoustic studies. [ABSTRACT FROM AUTHOR]

Underwater gliders have enormous potential for applications such as ocean exploration, the classification of large marine mammals, maritime surveillance, reconnaissance missions and maritime defense. Hydrophones mounted on an underwater glider need to be lightweight due to the compact size of the glider. The acceleration response caused by structural vibrations and changes in motion velocity, due to the continuous motion state of underwater gliders, becomes an important source of noise. In this paper, based on an acceleration cancellation principle, a tangential cylindrical hydrophone with high sound pressure sensitivity and low acceleration response is proposed. Modelling studies demonstrate that the axial acceleration sensitivity of the hydrophone can be reduced by 60 dB (re 1 V·s2/m), and the structural symmetry is the decisive factor affecting the effectiveness of acceleration cancellation. Hydrophone sample testing validated the acceleration cancellation principle. An experimental test of the hydrophone shows that the sound pressure sensitivity is −183.9 ± 2.0 dB (re 1 V/μPa), which is consistent with numerical simulations. Further, we analyzed several factors that may lead to a discrepancy between the measured and simulated values of hydrophone acceleration sensitivity. Our work demonstrates that the proposed hydrophone design can be beneficial for improving the acoustic performance of underwater gliders. [Display omitted] • Design a hydrophone specifically for underwater gliders with a high sound pressure sensitivity. • Prove advantages of the tangential cylindrical hydrophone for the design of a compact and lightweight hydrophone. • Validate the effectiveness of the acceleration cancellation principle. • Analyze the factors affecting the effectiveness of the acceleration cancellation principle. • Provide a method for reducing the vibration noise of underwater gliders retrofitted with hydrophones. [ABSTRACT FROM AUTHOR]

This paper is based on a project titled underwater acoustic communication in which communication is performed between transmitter and receiver side underwater using water as a channel; data are is transmitted through a piezo transducer underwater, which are then be received by a receiver, i.e., a wireless hydrophone. Signal processing and analysis are performed on the received wireless signals. Data reception and propagation are important parts on the receiver side, which involve conditioning and processing of the received signal. Morse code is used to detect the signals and processed data, which are then analyzed using MATLAB simulation software.

Sonosensitive perfluorocarbon F8TAC18-PFOB emulsion is under development to enhance heating, increase thermal contrast, and reduce treatment times during focused ultrasound tumor ablation of highly perfused tissue. The emulsion previously showed enhanced heating during ex vivo and in vitro studies. Experiments were designed to observe the response in additional scenarios by varying focused ultrasound conditions, emulsion concentrations, and surfactants. Most notably, changes in acoustic absorption were assessed with MR-ARFI. Phantoms were developed to have thermal, elastic, and relaxometry properties similar to those of ex vivo pig tissue. The phantoms were embedded with varying amounts of F8TAC18-PFOB emulsion or lecithin-PFOB emulsion, between about 0.0-0.3% v:w, in 0.05% v:w increments. MR-ARFI measurements were performed using a FLASH-ARFI-MRT sequence to obtain simultaneous displacement and temperature measurements. A Fabry-Perot hydrophone was utilized to observe the acoustic emissions. Susceptibility-weighted imaging and relaxometry mapping were performed to observe concentration-dependent effects. 19F diffusion-ordered spectroscopy NMR was used to measure the diffusion coefficient of perfluorocarbon droplets in a water emulsion. Increased displacement and temperature were observed with higher emulsion concentration. In semi-rigid MR-ARFI phantoms, a linear response was observed with low-duty cycle MR-ARFI sonications and a mono-exponential saturating response was observed with sustained sonications. The emulsifiers did not have a significant effect on acoustic absorption in semi-rigid gels. Stable cavitation might also contribute to enhanced heating.

This letter proposes a novel dynamic range extension method using an instantaneous frequency (IF)-tracking method for heterodyne fibre optic hydrophones (FOHs). IFs are used to compensate for large signal amplitudes in the demodulator. Theoretical analysis and simulation prove the effectiveness of the proposed algorithm. Simulation results achieve at least 19.76 dB dynamic range improvement, demonstrating great potential for extending FOHs for hydroacoustic detection and communication applications. [ABSTRACT FROM AUTHOR]

Spiny lobster Panulirus homarus is one of many important economic fishery resources in Indonesia. Continuous exploitation activities in the natural habitat can potentially disturb the sustainability of lobster resources. This species is known to produce sound with certain characteristics and highly dependent on environmental changes. This study aimed to investigate the characteristics of sound as a representation of behavior. The sound produced by P. homarus was recorded for 24 hours using a hydrophone (a passive acoustic technique). The hydrophone converts the sound wave produced by the lobsters into electric voltage in millivolts, then were converted to a digital number, in order to be saved in a virtual format with the *.wav extension. The video system captured data on behaviors of resting, territoriality, aggression, and social attitudes. The results showed that P. homarus emitted rasp, slow rattle, and popping type of sound, with certain characteristics. All sounds types were characterized by a broadband frequency (4 - 20 kHz), and a source level ranging from 125 - 145 dB re 1 µPa. Rasp sound consisting of 12 - 40 pulses with a sound duration of 100 - 400 ms, represents a defensive behavior. Slow rattle sound with 2 - 7 pulses did not represent a specific behavior and it is dominant during the night. However, the popping sound with only one pulse represented feeding behavior. [ABSTRACT FROM AUTHOR]

A multi-resonance Cymbal hydrophone for detection of the open-circuit self-contained underwater breathing apparatus (scuba) diver was designed and fabricated in this work, which has the advantages of multi-resonant frequency, high sensitivity, and narrow bandwidth. By using standard hydrophones, the underwater acoustic signal of the open-circuit scuba diver in the pool was collected and the characteristics of the signal were analyzed: the signal was mainly distributed in high frequency and low frequency. According to this characteristic, a Cymbal hydrophone with multi-resonance frequencies was designed in the finite element method, and the resonant frequency, receiving sensitivity, and bandwidth of the hydrophone were calculated. The accuracy of the calculation was verified with the performance test of the prototypes fabricated in this work. Finally, the underwater acoustic signal of an open-circuit scuba diver in the pool was tested by the prototype to demonstrate that the multi-resonance Cymbal hydrophone developed in this paper can be used for open-circuit scuba diver detection. [ABSTRACT FROM AUTHOR]

Single modality wireless power transfer has limited depth for mm-sized implants across air/tissue or skull/tissue interfaces because they either suffer from a high loss in tissue (RF, optical) or high reflection at the medium interface [ultrasound (US)]. This article proposes an RF-US relay chip at the media interface avoiding the reflection at the boundary and enables efficient wireless powering to mm-sized deep implants across multiple media. The relay chip rectifies the incoming RF power through an 85.5% efficient RF inductive link (across air) using a multi-output regulating rectifier (MORR) with 81% power conversion efficiency (PCE) at 186 mW load and transmits using adiabatic power amplifiers (PAs) to the implant in order to minimize cascaded power loss. To adapt US focus to implant movement or placement, beamforming was implemented using six channels of US PAs with two-bit phase control (0°, 90°, 180°, and 270°) and three different amplitudes (6–29, 4.5, and 1.8 V) from the MORR. The adiabatic PA contributes a 30%–40% increase in efficiency over class-D and beamforming increases the efficiency by 251% at 2.5 cm over fixed focusing. The proof-of-concept powering system for a retinal implant, from an external PA on a pair of glasses to a hydrophone with 1.2 cm (air) + 2.9 cm (agar eyeball phantom in mineral oil) separation distance, had a power delivered to the load (PDL) of 946 $\mu \text{W}$. The 2.3 mm × 2 mm relay chip was fabricated in a 180 nm high-voltage (HV) BCD process. [ABSTRACT FROM AUTHOR]

Understanding the properties of wildfire-disrupted catchments is crucial for managing river floods and landslide risks. Using a hydrophone, we investigated the changes in sediment supply conditions in small mountainous catchments (30.8 ha) in southern Korea for 6 years (March 2014–December 2019). Bedload transport rates mostly increased in burned catchments 1–2 years post-wildfire (early post-fire sediment regime) but decreased 3 years post-wildfire owing to the coverage of burned slopes (late post-fire sediment regime). Landslides triggered 5 years post-wildfire increased the bedload transport rates by approximately one order of magnitude (post-landslide sediment regime). Although sediment activity decreased in wildfire-disturbed catchments after recovery of the ground-cover layer 1–3 years post-fire, thy increased during events such as landslides. Furthermore, even in undisturbed mountainous catchments (139.7 ha), bedload transport rates increased after intense rainstorm events (≥100.0 mm), with this change lasting for approximately 2 years. Our observations showed that the forest restoration after a wildfire should be planned and implemented from a min- to long-term perspective. In addition, during rainstorms, the relationship between flow and bedload transport showed large variability even in undisturbed catchments. Furthermore, surrogate monitoring using a hydrophone was useful in understanding the changes in bedload transport characteristics according to various supply conditions of the catchment. [ABSTRACT FROM AUTHOR]

A single-hydrophone ocean glider was deployed within a cabled hydrophone array to demonstrate a framework for estimating population density of fin whales (Balaenoptera physalus) from a passive acoustic glider. The array was used to estimate tracks of acoustically active whales. These tracks became detection trials to model the detection function for glider-recorded 360-s windows containing fin whale 20-Hz pulses using a generalized additive model. Detection probability was dependent on both horizontal distance and low-frequency glider flow noise. At the median 40-Hz spectral level of 97 dB re 1 μPa2/Hz, detection probability was near one at horizontal distance zero with an effective detection radius of 17.1 km [coefficient of variation (CV) = 0.13]. Using estimates of acoustic availability and acoustically active group size from tagged and tracked fin whales, respectively, density of fin whales was estimated as 1.8 whales per 1000 km2 (CV = 0.55). A plot sampling density estimate for the same area and time, estimated from array data alone, was 1.3 whales per 1000 km2 (CV = 0.51). While the presented density estimates are from a small demonstration experiment and should be used with caution, the framework presented here advances our understanding of the potential use of gliders for cetacean density estimation. [ABSTRACT FROM AUTHOR]

Dolphins gain information through echolocation, a publicly accessible sensory system in which dolphins produce clicks and process returning echoes, thereby both investigating and contributing to auditory scenes. How their knowledge of these scenes contributes to their echoic information-seeking is unclear. Here, we investigate their top–down cognitive processes in an echoic matching-to-sample task in which targets and auditory scenes vary in their decipherability and shift from being completely unfamiliar to familiar. A blind-folded adult male dolphin investigated a target sample positioned in front of a hydrophone to allow recording of clicks, a measure of information-seeking and effort; the dolphin received fish for choosing an object identical to the sample from 3 alternatives. We presented 20 three-object sets, unfamiliar in the first five 18-trial sessions with each set. Performance accuracy and click counts varied widely across sets. Click counts of the four lowest-performance-accuracy/low-discriminability sets (X = 41%) and the four highest-performance-accuracy/high-discriminability sets (X = 91%) were similar at the first sessions' starts and then decreased for both kinds of scenes, although the decrease was substantially greater for low-discriminability sets. In four challenging-but-doable sets, number of clicks remained relatively steady across the 5 sessions. Reduced echoic effort with low-discriminability sets was not due to overall motivation: the differential relationship between click number and object-set discriminability was maintained when difficult and easy trials were interleaved and when objects from originally difficult scenes were grouped with more discriminable objects. These data suggest that dolphins calibrate their echoic information-seeking effort based on their knowledge and expectations of auditory scenes. [ABSTRACT FROM AUTHOR]

Earthquake magnitude calibration using hydrophone records has been carried out at Campi Flegrei caldera, an active area close to the highly populated area of Naples city, partly undersea. Definite integrals of the hydrophone records amplitude spectra, between the limits of 1 and 20 Hz, were calculated on a set of small volcano-tectonic earthquakes with moment magnitudes ranging from 1 to 3.3. The coefficients of a linear relationship between the logarithm of these integrals and the magnitude were obtained by linear optimization, thus defining a useful equation to calculate the moment magnitude from the hydrophone record spectra. This method could be easily exported to other volcanic areas, where submerged volcanoes are monitored by networks of hydrophones and seismic sensors on land. The proposed approach allows indeed magnitude measurements of small magnitude earthquakes occurring at sea, thus adding useful information to the seismicity of these volcanoes. [ABSTRACT FROM AUTHOR]

Abundance estimates of cetaceans are often acquired through capture‐recapture analysis of photographically identified individuals. An alternative method, using capture‐recapture of individually distinct signature whistles detected from acoustic underwater recording units, has recently been demonstrated. Here we investigate the effect of array configuration (1–3 hydrophones within 0.45 km2) and recording duty cycles (six variations of 33%, 50%, or 66% sampling periods) on the detection rate of dolphin signature whistles. Twenty‐one signature whistle types were identified and used to create capture histories for each hydrophone and all potential array configurations. Open population models were used to estimate capture probabilities and precision for all data sets. The effect of different duty cycles on detectability were investigated by artificially applying six duty cycles to the continuously recorded data. Results demonstrate that location is more important than redundancy in small‐scale arrays, even with detection distances as small as 750 m, and that duty cycling can increase survey durations without decreasing detectability. To acoustically sample intermittent signals of dispersed populations, it is more effective to space hydrophones further apart, in known high‐use areas. This study provides insight into the application of capture‐recapture to signature whistles, improving methods for long‐term, noninvasive monitoring of elusive delphinids. [ABSTRACT FROM AUTHOR]

The demodulation algorithm based on 3 × 3 coupler in a fiber-optic hydrophone array has gained extensive attention in recent years. The traditional method uses a circulator to construct the normal path-match interferometry; however, the problem of increasing the asymmetry of the three-way signal to be demodulated is easily overlooked. To provide a solution, we report a pretreatment method for hydrophone array based on 3 × 3 coupler demodulation. We use cubic spline interpolation to perform nonlinear fitting to the reflected pulse train and calculate the peak-to-peak values of the single pulse to determine the light intensity compensation coefficient of the interference signal, so as to demodulate the corrected three-way interference signal. For experimental verification, ultra-weak fiber Bragg gratings (uwFBGs) with reflectivity of −50 dB are applied to construct a hydrophone array with 800 sensors, and a vibratory liquid column method is set up to generate a low-frequency hydroacoustic signal. Compared to the traditional demodulation algorithm based on a 3 × 3 coupler, the pretreatment method can improve the consistency of interference signals. The Lissajous figures show that cubic spline interpolation can improve the accuracy of monopulse peak seeking results by about 1 dB, and intensity compensation can further lead to a much lower noise density level for the interference pulse amplitude—specifically, more than 7 dB at 5~50 Hz—and the signal-to-noise ratio is improved by approximately 10 dB at 10 Hz. The distinct advantages of the proposed pretreatment method make it an excellent candidate for a hydrophone array system based on path-match interferometry. [ABSTRACT FROM AUTHOR]