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Hydrophone is a key component of marine seismic exploration systems, divided into a scalar hydrophone and vector hydrophone. The electrochemical vector hydrophone has attracted much attention due to its high sensitivity and low-frequency detection capability. With the development of noise reduction technology, high-frequency noise has been effectively suppressed, while low-frequency noise is still difficult to control, which has become a key issue in the monitoring of underwater target radiation noise. The traditional electrochemical vector hydrophone based on the molecular electron transfer (MET) principle is limited in the working bandwidth in the low-frequency band, which affects the detection capability of low-frequency radiation signals from underwater targets. In order to solve this problem, a frequency response extension method of a MET electrochemical vector hydrophone based on dynamic feedback network is proposed. By introducing a dynamic force balance negative feedback system based on a digital signal processor (DSP), the working bandwidth of the hydrophone is extended, and the detection capability of low-frequency signals is enhanced. At the same time, the system has field adjustability and can resist the long-term system frequency characteristic drift. Experimental results show that the proposed method effectively improves the frequency response performance of the electrochemical vector hydrophone, providing a new technical solution for its application in the monitoring of low-frequency radiation noise from underwater targets. [ABSTRACT FROM AUTHOR]

Laser heterodyne interferometry plays a crucial role in measuring the velocity of water particles during the calibration of hydrophones with the optical method. The velocity of water particles acts as an indicator of acoustic-pressure variations and can be used to evaluate the stability of the acoustic field. The calibration of hydrophones requires a stable acoustic field environment; currently, though, the assessment of acoustic field stability is largely subjective. This study introduces the Normalized Dynamic Time-Warping (NDTW) algorithm, which objectively evaluates acoustic field stability. Sine-fitting is applied to the region of interest in the measured signal to obtain a reference signal. Subsequently, the NDTW algorithm is used to calculate the difference between the measured and reference signals, enabling the assessment of acoustic field stability. The NDTW algorithm effectively identifies subtle differences between signals and addresses the accumulation errors arising from varying signal lengths. The calibration results showed that for signals of high quality within the identified frequency band, the calibration outcomes obtained using the NDTW algorithm deviated from the reciprocity method by no more than 0.7 dB. For frequency bands with poor signal quality identified by the NDTW algorithm, the deviation between the calibration results and the reciprocity method exceeded 0.7 dB. [ABSTRACT FROM AUTHOR]

The characterization of gas–liquid two-phase flow patterns is crucial for monitoring stability in industrial applications. However, the impact of these flow patterns on gas–liquid two-phase flow-induced sound (GTFIS) emissions remains inadequately understood. In this paper, the GTFIS signals at high liquid velocities within a horizontal pipe are captured using precision hydrophone. A novel approach for the analysis of acoustic signals that synergistically combines Variational Mode Decomposition, Singular Value Decomposition, and nonlinear signal processing methods is proposed to assess the flow dynamics. The results show that the GTFIS signals exhibit chaotic characteristics. Two distinct Hurst exponents are observed for each acoustic signal: one is greater than 0.5 and the other is less than 0.5. The coexistence of randomly moving small bubbles and intermittent bubbles contributes to an increase in the complexity of the attractor phase trajectory of acoustic signals, resulting in a maximum value in the correlation dimension. The expansion radius and correlation dimension of mesoscale acoustic signals can serve as early warning indicators for the transition from dispersed bubble flow to slug flow. In conjunction with the characteristic parameters of multi-scale entropy, the flow patterns can be effectively characterized. [ABSTRACT FROM AUTHOR]

Low-frequency ocean noise (50–500 Hz) was recorded by a single omnidirectional hydrophone in the open waters of the Chukchi Plateau from 31 August 2021 to 6 September 2021 (local time). After other non-wind interference was filtered out, wind-generated noise source levels (NSLs) were extracted from the wind-generated noise. The correlation coefficients between the one-third octave wind-generated NSLs and sea surface wind speed exceed 0.84, an improvement of approximately 10% compared to those between the raw data and the wind speed. For 200–500 Hz, the wind-generated NSLs are highly consistent with Wilson's (1983) estimated curve. The 50–300 Hz results closely match those of Chapman and Cornish (1993) from vertical line array (VLA) measurements. Both demonstrate the feasibility of extracting wind-generated NSLs by utilizing a single omnidirectional hydrophone in the Chukchi Plateau's open waters. Furthermore, the research results of wind speed dependence and frequency dependence can be applied to calculate wind-generated NSLs in the Chukchi Plateau. Wind-derived ocean ambient noise data are useful for background correction in underwater target detection, recognition, tracking, and positioning. [ABSTRACT FROM AUTHOR]

The Sagnac interferometer-based fiber-optic hydrophone (S-FOH) exhibits a frequency-dependent response, causing the output signal to deviate from the original acoustic signal, with severe cases leading to signal distortion. A response equalization demodulation algorithm is demonstrated to recover high-fidelity acoustic signals from interference phase signals. An eight-sensor S-FOH array featuring an alternative quadrature phase bias scheme is demonstrated, and experimental verification of the response equalization demodulation algorithm is performed. The temporal relationship of phase modulation pulses and sampling light pulses is analyzed, and a demodulation algorithm is introduced to obtain the phase difference of the Sagnac interferometer. The acoustic pressure sensitivity is equalized to be flat with an average of −135.0 ± 0.4 dB from 10 to 2032 Hz. The pulse response of the S-FOHA after the equalization algorithm is highly similar to the PZT hydrophone output signal, with a correlation coefficient of 0.987. [ABSTRACT FROM AUTHOR]

Background Purpose Methods Results Conclusion Protoacoustics has emerged as a promising real‐time range measurement method for proton therapy. Optical hydrophones (OHs) are considered suitable to detect protoacoustic waves owing to their ultracompact size and high sensitivity. In our previous research, we demonstrated that the time‐of‐arrival (TOA) measured by an OH showed good agreement with the simulated ground truth in a homogeneous medium.The purpose of the study was to experimentally evaluate the accuracy of the TOA and compression peak pressures detected by the OH. Protoacoustic waves that undergo the typical distortions occurring in the human body were investigated. In such cases, the use of small detectors such as OHs is desirable to minimize the effects of detector size and directivity.A 100‐MeV proton pencil beam emitted from a fixed‐field alternating gradient accelerator was irradiated onto a homogeneous water phantom and a water phantom with a half‐ or full‐sized silicone plate downstream of the Bragg peak (BP) or a bone plate that covered half of the beam cross‐section in the beam path. The OH was shifted 70 mm laterally across the beam axis downstream of the BP to measure the protoacoustic waves. The k‐WAVE acoustic wave transport simulation was employed as the ground truth. The TOA and the first compression peak pressures were compared between the simulation and experiment.The TOA deviation against the ground truth was primarily attributed to alignment errors of the measurement devices and phantoms, with deviations of < 1 mm. The peak pressure distribution closely resembled the ground truth, with FWHM differences of 0.0%–3.0% for the tested geometries.The OH was able to determine the TOA and peak pressures with sufficient accuracy in heterogeneous phantoms, even without considering the effect of the size of the detector or directivity on the measurements. [ABSTRACT FROM AUTHOR]

Objective. To evaluate the feasibility of transspine focused ultrasound using simulation-based phase corrections from a CT-derived ray acoustics model. Approach. Bilateral transspine focusing was performed in ex vivo human vertebrae with a spine-specific ultrasound array. Ray acoustics-derived phase correction was compared to geometric focusing and a hydrophone-corrected gold standard. Planar hydrophone scans were recorded in the spinal canal and three metrics were calculated: target pressure, coronal and sagittal focal shift, and coronal and sagittal Sørensen–Dice similarity to the free-field. Post hoc analysis was performed in silico to assess the impact of windows between vertebrae on focal shift. Main results. Hydrophone correction reduced mean sagittal plane shift from 1.74 ± 0.82 mm to 1.40 ± 0.82 mm and mean coronal plane shift from 1.07 ± 0.63 mm to 0.54 ± 0.49 mm. Ray acoustics correction reduced mean sagittal plane and coronal plane shift to 1.63 ± 0.83 mm and 0.83 ± 0.60 mm, respectively. Hydrophone correction increased mean sagittal similarity from 0.48 ± 0.22 to 0.68 ± 0.19 and mean coronal similarity from 0.48 ± 0.23 to 0.70 ± 0.19. Ray acoustics correction increased mean sagittal and coronal similarity to 0.53 ± 0.25 and 0.55 ± 0.26, respectively. Target pressure was relatively unchanged across beamforming methods. In silico analysis found that, for some targets, unoccluded paths may have increased focal shift. Significance. Gold standard phase correction significantly reduced coronal shift and significantly increased sagittal and coronal Sørensen–Dice similarity (p < 0.05). Ray acoustics-derived phase correction reduced sagittal and coronal shift and increased sagittal and coronal similarity but did not achieve statistical significance. Across beamforming methods, mean focal shift was comparable to MRI resolution, suggesting that transspine focusing is possible with minimal correction in favourable targets. Future work will explore the mitigation of acoustic windows with anti-focus control points. [ABSTRACT FROM AUTHOR]

Ultrasound imaging technology is crucial for diagnostics in both biomedical and industrial fields. However, pushing the boundaries of resolution and overcoming difficulties presented by complex environments remain challenging. Traditionally, diffraction limits resolution due to the loss of valuable subwavelength information carried by evanescent waves. Scattering further complicates imaging through intricate materials or obstructions. Here, we presented an approach for achieving far‐field subwavelength resolution ultrasound imaging through heterogeneous mediums is presented. This method converts inaccessible evanescent wave into detectable propagating waves. These waves are then captured by a far‐field hydrophone and use in conjunction with the joint‐sparsity algorithm to reconstruct the object. These results demonstrate a remarkable resolution of 1/5λ, significantly surpassing the diffraction limit. This subwavelength imaging performance exhibits remarkable stability even in the presence of unwanted scatterers. The two‐dimensional imaging results and the influence of measurement parameters are further explored. These findings suggest that the combination of metagrating illumination and the joint‐sparsity algorithm offers a promising avenue for recovering subwavelength object information in the far‐field, eliminating the need for near‐field markers. This work paves the way for high‐fidelity subwavelength ultrasound imaging in heterogeneous environments, holding promising potential for advancements in biomedical imaging, nondestructive testing, and other related fields. [ABSTRACT FROM AUTHOR]

Acoustic microscopy uses ultra-high frequency (UHF) ultrasound transducers over 80 MHz to perform high-resolution imaging. The pressure output of these transducers is unknown, as commercial calibrated hydrophones can measure pressure for transducers with frequencies only up to 80 MHz. This study used gas vesicle nanostructures (GVs) that collapse at 571 kPa to estimate the pressure of UHF transducers at 40, 80, 200, and 375 MHz. Agarose phantoms containing GVs were made, and a baseline ultrasound image was performed at low pressure to prevent GV collapse. Sections within the phantom were scanned at varying voltage to determine the GV collapse threshold. The pressure at full driving voltage was then calculated, assuming a linear relation between transducer voltage and pressure. The pressure calculated for the 40 MHz transducer was 2.2 ± 0.1 MPa at 21 °C. Using a hydrophone, the measured pressure was 2.1 ± 0.3 MPa, a difference of <2%, validating the method at this frequency. The pressure calculated for the other transducers was 2.0 ± 0.1 MPa (80 MHz), 1.2 ± 0.1 (200 MHz), and 1.05 ± 0.17 (375 MHz at 37 °C). This study addresses the challenge of estimating pressure output from UHF ultrasound transducers, demonstrating that the pressure output in the 40–400 MHz frequency range can be quantified. [ABSTRACT FROM AUTHOR]

The ambient noise model of isotropic fields is not applicable to shallow-located platforms in the deep ocean, and the conventional methods for estimating the sound-ray-arrival-grazing-angle of targets do not account for the effects of surface noise. Therefore, target parameter estimation methods based on a single vector hydrophone are explored in this study. The approach used in this study integrates the hydroacoustic physical model, signal processing method, and ocean ambient. A time-domain model of the vector field of deep ocean ambient noise was developed for receivers positioned at shallow depths, followed by derivation of the covariance matrix of the single vector hydrophone based on this model. Subsequently, a target signal-to-noise ratio (SNR) estimation method using the covariance matrix derived from the single vector hydrophone was formulated. This method effectively addresses the challenge of distinguishing between target signal and noise by transforming the power estimation problem into a covariance matrix solving the task. Finally, a refined approach for estimating the sound-ray-arrival-grazing-angle of target is proposed, aiming to theoretically mitigate the impact of surface noise on the target signal. The experimental data obtained from a deep ocean region in the South China Sea indicate that the findings obtained using the method proposed in this study are consistent with the reference values derived from automatic identification system information. The method also demonstrates reliable estimation results even when the SNR exceeds –5 dB. The conceptual framework developed for SNR and sound-ray-arrival-grazing-angle estimation in this study can be readily applied to other ambient models, indicating potential applications in engineering field. The primary objective of the study was to enhance and augment underwater acoustic signal processing methods for shallow receivers deployed in the deep ocean. [ABSTRACT FROM AUTHOR]

Copyright of Piezoelectrics & Acoustooptics is the property of Piezoelectric & Acoustooptic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present experimental study assessed the viability of utilizing an acoustic emission signal as a monitoring instrument to predict the chemical characteristics of wine throughout the alcoholic fermentation process. The purpose of this study is to acquire the acoustic emission signals generated by CO₂ bubbles to calculate the must density and monitor the kinetics of the alcoholic fermentation process. The kinetics of the process were evaluated in real time using a hydrophone immersed in the liquid within the fermentation tank. The measurements were conducted in multiple fermentation tanks at a winery engaged in the production of wines bearing the Rioja Denomination of Origin (D.O.) designation. Acoustic signals were acquired throughout the entirety of the fermentation process, via a sampling period of five minutes, and stored for subsequent processing. To validate the results, the measurements obtained manually in the laboratory by the winemaker were collected during this stage. Signal processing was conducted to extract descriptors from the acoustic signal and evaluate their correlation with the experimental data acquired during the process. The results of the analyses confirm that there is a high linear correlation between the density data obtained from the acoustic analysis and the density data obtained at the laboratory level, with determination coefficients exceeding 95%. The acoustic emission signal is a valuable decision-making tool for technicians and winemakers due to its sensitivity when describing variations in kinetics and density during the alcoholic fermentation process. [ABSTRACT FROM AUTHOR]

This 11-year case study describes the acoustic behaviour of a resident Indian Ocean humpback dolphin during commercial swim-with-dolphin activities in Mozambique. Combining data collected using low-cost action cameras with full bandwidth hydrophone recordings, we identified a temporally stable stereotyped whistle contour that met the SIGnature IDentification bout criteria. This whistle was produced with potential information-enhancing features (bi-phonation and subtle variations in frequency modulation). This case study provides evidence for a single, stable, stereotyped call type from a single individual in a mixed species group, contributing to the growing body of evidence for possible signature whistle use in the Sousa genus. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to design a small-size conformable flexible micro-electro-mechanical system (MEMS) vector hydrophone to meet the miniaturization requirements of unmanned underwater vehicle. Design/methodology/approach: The cilia receive the acoustic signal to oscillate to cause changes in the stress on the beam, which in turn causes changes in the piezoresistive resistance on the beam, and changes in the resistance cause changes in the output voltage. Findings: The results show that the flexible hydrophone in the paper has a sensitivity of −182 dB@1 kHz (re 1V/µPa) at 1 Pa sound pressure, can detect low-frequency hydroacoustic signals from 20 to 550 Hz and has good spatial directivity, and the flexible substrate permits the hydrophone to realize bending deformation, which can be well attached to the surface of the object. Originality/value: In this study, a finite element simulation model of the hydrophone microstructure is constructed and its performance is verified by simulation. The success rate of the proposed MEMS transfer process is as high as 94%, and the prepared piezoresistors exhibit excellent resistance characteristics and high consistency. These results provide innovative ideas to enhance the performance and stability and achieve miniaturization of hydrophones. [ABSTRACT FROM AUTHOR]

This letter presents a novel approach to sparse Bayesian underwater acoustic signal direction estimation. The proposed method incorporates interpolation of the coprime array and signal subspace fitting. It addresses the limitations of the hydrophone coprime array in utilizing all array elements' information and mitigates the interference of ocean noise in shallow waters, which impairs the accuracy and resolution of target direction estimation. Firstly, the hydroacoustic signals are received using a coprime array, then the missing information is filled by interpolating the virtual array elements in the virtual domain, and by optimizing the design of the atomic norm and reconstructing the covariance matrix, the direction-of-arrival (DOA) estimation is performed using all the information of the received signal. Then, the received signal is reconstructed in conjunction with the reconstructed covariance signal subspace, which effectively reduces the impact of background noise. Finally, we derive an off-grid sparse model for the reconstructed signal by exploiting sparsity in the null domain and use Bayesian learning to compute the maximum a posteriori probability of the source signal, thus achieving DOA estimation. The results of numerical simulations and sea trial experimental data indicate that the use of subarrays comprising 5 and 3 array elements, respectively, is sufficient to effectively estimate 12 source angles. Furthermore, the estimation of the DOA can be accurately carried out under low signal-to-noise ratio conditions. This method effectively utilizes the degrees of freedom provided by the virtual array, reducing noise interference, and exhibiting better performance in terms of positioning accuracy and algorithm stability. [ABSTRACT FROM AUTHOR]

Underwater direction-of-arrival (DOA) tracking using a hydrophone array is an important research subject in passive sonar signal processing. In this study, a DOA tracking algorithm based on a novel beam-domain signal processing technique is proposed to ensure robust DOA tracking of an interested underwater target under a low signal-to-noise ratio (SNR) environment. Firstly, the beam-based observation is designed and proposed, which innovatively applies beamforming after array-based observation to achieve specific spatial directivity. Next, the proportional–integral–differential (PID)-optimized Olen–Campton beamforming method (PIDBF) is designed and proposed in the beamforming process to achieve faster and more stable sidelobe control performance to enhance the SNR of the target. The adaptive dynamic beam window is designed and proposed to focusing the observation on more likely observation area. Then, by utilizing the extended Kalman filter (EKF) tracking framework, a novel PIDBF-optimized beam-domain DOA tracking algorithm (PIDBF-EKF) is proposed. Finally, simulations with different SNR scenarios and comprehensive analyses are made to verify the superior performance of the proposed DOA tracking approach. [ABSTRACT FROM AUTHOR]

Investigating anthropogenic acoustic disturbance and sound exposure in marine mammals requires evaluation of experimental approaches used to measure the sound levels experienced by the subjects. In previous research, exposure of California sea lions (Zalophus californianus) to eight narrow noise bands was estimated as the mean sound pressure level (SPL) measured by hydrophones placed at multiple locations and depths in a pool. We compare this method of SPL estimation with SPLs measured with a sound recording tag ("D-tag"). Measurements were taken from (1) hydrophones at locations on a grid; (2) a D-tag at the same locations; (3) a D-tag attached in its housing to a harness on a sea lion swimming freely in the pool; (4) a D-tag in its housing in one position in the pool; (5) a D-tag on the sea lion in one position in the pool; and (6) a D-tag turning in one location in the pool without its housing, in its housing, and on the sea lion while she rotated on her body axis. The SPLs recorded by the D-tag on a freeswimming sea lion were ~8 to 10 dB lower than those measured by the grid hydrophones, and the differences varied by frequency. These differences in SPL are caused by a combination of the directionality associated with the D-tag itself, the presence of the housing, acoustic effects of the sea lion's body, and periods that the D-tag was out of the water during respirations. Measuring mean sound levels in test pools using hydrophones deployed on grids is valid; however, attaching tags to wild marine mammals may be more feasible than using hydrophone grids at sea. We summarize considerations when selecting a method to fit the design of future research. [ABSTRACT FROM AUTHOR]

This paper is dedicated to the acoustic inversion of the vertical sound speed profiles (SSPs) in the underwater marine environment. The method of automatic differentiation is applied for the first time in this context. Representing the finite-difference Padé approximation of the propagation operator as a computational graph allows for the analytical computation of the gradient with respect to the SSP directly within the numerical scheme. The availability of the gradient, along with the high computational efficiency of the numerical method used, enables rapid inversion of the SSP based on acoustic measurements from a hydrophone array. It is demonstrated that local optimization methods can be effectively used for real-time sound speed inversion. Comparative analysis with existing methods shows the significant superiority of the proposed method in terms of computation speed. [ABSTRACT FROM AUTHOR]

During the 2018 Kīlauea eruption, over half the erupted lava was deposited on the seafloor. Lava flows crossing the shoreline generated sounds that were recorded by a network of hydrophones. We show that short‐duration, broadband signals associated with lava‐water interactions occurred throughout the eruption but increased in number when the Ahalanui ocean entry initiated on July 11. These terminated in early August coincident with the eruption's end. We compare hydroacoustic data with transmission loss models and eruption photographs to show that coastal explosive activity was poorly recorded by the hydrophone network. Similarly, strong hydroacoustic signals did not correlate with observed activity. These results suggest that acoustic signals were generated by lava flowing up to 100 s of meters offshore. Offshore lava flows can be hazardous to boaters, but hydrophones provide a means by which these hazards can be detected. Plain Language Summary: During the 2018 eruption of Kīlauea volcano, Hawai'i, lava flowed past the coastline and into the sea where it was deposited on the volcano's submarine flank. In this study we show that the interaction of lava and sea water created noise that was detected by a network of hydrophones (underwater microphones) placed offshore. Lava‐water interactions that occurred very close to the coastline, however, were not well‐recorded by the hydrophones, suggesting that sound was trapped in the shallow water. Other strong sounds were recorded when no obvious activity was visible at the coast. These observations suggest lava was flowing much farther offshore than was observed from the surface, potentially posing a threat to boaters and coastal observers. Key Points: Lava flows entering the ocean during the 2018 Kīlauea eruption generated sounds that were detected by hydrophonesExplosive activity observed near the coastline was only weakly detected by the hydrophonesSignals detected by the hydrophones may have initiated >100 m from the coast, suggesting that lava advanced well offshore [ABSTRACT FROM AUTHOR]

In this article, I unravel how my artistic research, focusing on the sonic spectrum, can reflect on interspecies perception and communication within the Aquatocene, an era marked by humanity's deep involvement with aquatic environments. I coined the term Aquatocene to describe the state of waters in the Anthropocene. Through an interdisciplinary blending of art, science and technology, I examine the philosophical and methodological frameworks driving my artistic practice. With projects like Aquatocene and Atlantic Tales, I am to reimagine interspecies relationships while reflecting on life's interconnectedness in aquatic realms. My work echoes that of artists Kat Austen, Kasia Molga, B. R. Shailesh and Marco Barotti, who also address environmental issues. Our shared mission is to foster dialogue, raise awareness and inspire action in response to ecological challenges. I suggest we need to reconsider how artists and researchers illuminate our relationship with the natural world, both above and beneath the waves. Through interdisciplinary collaboration, within my art practice, I navigate in the Aquatocene with reverence, humility and responsibility towards the myriad coexisting species. With this text, I aim to guide readers through my projects, sharing the theoretical and practical processes that explore multispecies sensory perception and communication in a (geo)political pursuit of love – an empathetic strategy to refine coexistence through sonic presence. [ABSTRACT FROM AUTHOR]

Ocean gliders are versatile and efficient passive acoustic monitoring platforms in remote marine environments, but few studies have examined their potential to monitor ship underwater noise. This study investigates a Slocum glider's capability to assess ship noise compared to the ability of fixed observers. Trials were conducted in shallow coastal inlets and deep bays in Newfoundland, Canada, using a glider, hydrophone array, and single-moored system. The study focused on (1) the glider's self-noise signature, (2) range-depth-dependent propagation loss (PL) models, and (3) identifying the location of the vessel to the glider using glider acoustic measurements. The primary contributors to the glider's self-noise were the buoyancy pump and rudder. The pitch-motor noise coincided with the buoyancy pump activation and did not contribute to the glider self-noise in our experiments. PL models showed that seafloor bathymetry and sound speed profiles significantly impacted estimates compared to models assuming flat and range-independent profiles. The glider's performance in recording ship noise was superior to that of other platforms. Using its hydrophones, the glider could identify the bearing from the vessel, although a third hydrophone would improve reliability and provide range. The findings demonstrate that gliders can characterize noise and enhance our understanding of ocean sound sources. [ABSTRACT FROM AUTHOR]

Through extensive literature review, it has been found that sparse Bayesian learning (SBL) is mainly applied to traditional scalar hydrophones and is rarely applied to vector hydrophones. This article proposes a direction of arrival (DOA) estimation method for vector hydrophones based on SBL (Vector-SBL). Firstly, vector hydrophones capture both sound pressure and particle velocity, enabling the acquisition of multidimensional sound field information. Secondly, SBL accurately reconstructs the received vector signal, addressing challenges like low signal-to-noise ratio (SNR), limited snapshots, and coherent sources. Finally, precise DOA estimation is achieved for multiple sources without prior knowledge of their number. Simulation experiments have shown that compared with the OMP, MUSIC, and CBF algorithms, the proposed method exhibits higher DOA estimation accuracy under conditions of low SNR, small snapshots, multiple sources, and coherent sources. Furthermore, it demonstrates superior resolution when dealing with closely spaced signal sources. [ABSTRACT FROM AUTHOR]

Matched field processing (MFP) is an established technique for source localization in known multipath acoustic environments. Unfortunately, in many situations, imperfect knowledge of the actual propagation environment and sidelobes due to modal interference prevent accurate propagation modeling and source localization via MFP. To suppress the sidelobes and improve the method's robustness, a linear frequency-difference matched field processing (LFDMFP) method for estimating the source range is proposed. A two-neighbor-frequency high-order cross-spectrum between the measurement and the replica of each hydrophone of the vertical line array is first computed. The cost function can then be derived from the dual summation or double integral of the high-order cross-spectrum with respect to the depth of the hydrophones and the candidate sources of the replicas, where the range that corresponds to the minimum is the optimal estimation. Because of the larger modal interference distances, LFDMFP can efficiently provide only one optimal range within the same range search interval rather than some conventional matched field processing. The efficiency of the presented method was verified using simulations and experiments. The LFDMFP unambiguously estimated the source range in two experimental datasets with average relative errors of 2.2 and 1.9%. [ABSTRACT FROM AUTHOR]

In passive sonar systems, deviations from an ideal linear configuration can significantly impair the beamforming performance of towed hydrophone arrays. This paper presents a method aimed at improving the underwater acoustic signals in the presence of array distortion. The method is centered on a high-order time-delay difference estimation technique utilizing time-frequency autofocus. Initially, a detailed signal model is established that captures the distinctive characteristics of distorted arrays. Subsequently, an algorithm is introduced for high-order time-delay difference estimation to enhance signal fidelity by leveraging phase information within narrowband components originating from incidental acoustic sources. Additionally, a quality metric to evaluate these components is introduced, facilitating the practical implementation of the method. The effectiveness of the proposed approach is validated through both simulation and experimental results, demonstrating its superiority over existing techniques. Importantly, this method does not require prior knowledge of the distortion pattern, making it adaptable to various non-linear array configurations. [ABSTRACT FROM AUTHOR]

In 2007, the Littoral Acoustic Demonstration Center conducted a comprehensive experiment in the northern Gulf of Mexico to measure the three-dimensional acoustic field of a standard marine compressed-air source array used in seismic exploration. This study aims to enhance understanding of long-range acoustic propagation of the array signals, with focus on variations in received sound pressure levels and sound exposure levels (SELs) at various ranges from the source. These variations are influenced by factors, such as receiver depth, array orientation, and propagation conditions. The long-range measurements show that received peak pressure levels and SELs exhibit non-monotonic (oscillatory) behavior with range leading up to 10 dB increase in received levels at longer ranges. At ranges beyond 20 km, acoustic levels at the shallowest hydrophone consistently surpassed those at deeper ones by 3–10 dB, suggesting the impact of surface duct propagation effects. The results demonstrate that range-independent bathymetry leads to approximately 4 dB higher received acoustic levels than range-dependent propagation conditions. The measured long-range propagation acoustic metrics from controlled experiment provide a unique and critical dataset for validating both source and propagation model accuracy in predicting received sound pressure and SEL in the far-field of the source array. [ABSTRACT FROM AUTHOR]

In this paper, to counteract the sensitivity of the traditional Hough transform to noise and the fluctuations in parameter estimation, we propose a hyperbolic warping transform that integrates all interference fringes in the time–frequency domain to accurately estimate the motion parameters of a single hydrophone. This method can accurately estimate the target motion parameters, including the time of closest point of approach ( t C P A ), the ratio of the nearest distance to the speed ( b = r C P A / v ), and the waveguide invariant (β). The two algorithms are compared by simulation and sea trial experiments. Hyperbola-warping improves the noise immunity performance by 10 dB in simulation experiments, increases the detection range by 20% in sea trial experiments, and demonstrates that the method proposed in this paper has better noise resistance and practicality. [ABSTRACT FROM AUTHOR]

Deghosting of marine seismic data is an important and challenging step in the seismic processing flow. We describe a novel approach to train a supervised convolutional neural network to perform joint source and receiver deghosting of single‐component (hydrophone) data. The training dataset is generated by demigration of stacked depth migrated images into shot gathers with and without ghosts using the actual source and receiver locations from a real survey. To create demigrated data with ghosts, we need an estimate of the depth of the sources and receivers and the reflectivity of the sea surface. In the training process, we systematically perturbed these parameters to create variability in the ghost timing and amplitude and show that this makes the convolutional neural network more robust to variability in source/receiver depth, swells and sea surface reflectivity. We tested the new method on the Marmousi synthetic data and real North Sea field data and show that, in some respects, it performs better than a standard deterministic deghosting method based on least‐squares inversion in the τ‐p domain. On the synthetic data, we also demonstrate the robustness of the new method to variations in swells and sea‐surface reflectivity. [ABSTRACT FROM AUTHOR]

Copyright of Technisches Messen is the property of De Gruyter and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large reservoirs have areas dangerous for fish. For instance, water intake facilities, hydroelectric dams, etc. Therefore, it becomes necessary to protect or divert fish from such areas. One way to achieve this is to use loud underwater sound. Most fish are sensitive to noise. Acoustic underwater speakers, developed in recent years, transmit full-fledged sound information underwater. This made it possible to study the possibilities of scaring away fish by underwater sounds of various volumes and frequencies. The purpose of the experiments was the following: to set the dynamics of the sound volume attenuation, with increasing distance from the sound source; to study the fish reaction to different types of acoustic signal; to study the effectiveness of scaring fish with sounds of various volumes and frequencies; to set the duration of the effect of single and multiple acoustic scaring.

We introduce a tsunami warning technology towards a global real-time analysis. The technology is based on the analysis of acoustic signals generated together with the tsunami, due to the compression of the water layer. The acoustic signals propagate much faster than the tsunami, and thus can be recorded at hydrophone stations, which in turn enables the analysis in real-time. The presented technology comprises a collection of models that have been integrated into a software with the goal to make it operational, to complement efforts by warning centres and provide a more reliable assessment, globally. The main models that were integrated in the software are presented and briefly discussed. Test cases performed by the software are compared with DART buoy observations, showing satisfactory agreement though discrepancies arise in particular at far distances and locations separated by land. The calculation time of a full global-scale analysis is in the order of tens of seconds on a standard multi-core machine, without reliance on pre-computations, making it appropriate real-time forecast. [ABSTRACT FROM AUTHOR]

Flextensional transducers have been widely used as low-frequency projectors, and these characteristics can be used to develop hydrophones with wider receiver bandwidth and higher sensitivity than conventional products in low-frequency ranges. In this work, we designed flextensional hydrophones of all classes, and compared their acoustic receiver performance to select the most suitable class for a low-frequency broadband hydrophone. For this purpose, basic models of the hydrophones were constructed for all classes and the effects of various structural parameters on the acoustic receiver characteristics of the hydrophones were analyzed. Based on the results, the structure of the flextensional hydrophone of each class was designed to have the maximum receiver bandwidth by an optimization technique while maintaining the receiver voltage sensitivity over a certain level. A comparison of the designed performance led to the selection of the class IV flextensional hydrophone as the most promising one with the widest receiver fractional bandwidth and highest sensitivity. [ABSTRACT FROM AUTHOR]

A hydrophone was positioned underwater in both lotic and lentic habitats to determine whether the Growling Grass Frog Litoria raniformis major calls underwater. A microphone was positioned above the water surface a few metres from the hydrophone, and calls were recorded using a synchronised recording schedule for 4 months at each site. Litoria raniformis major calls were recorded by the hydrophone on 2 files from the lotic habitat and on 6 files from the lentic habitat. Underwater calling by L. r. major was recorded simultaneously with above-water calling at the lentic habitat and once at the lotic. The other underwater call event at the lotic habitat was recorded without any above-water calling recorded by the microphone. Underwater calling is hypothesised to be a response to physical contact by conspecifics. This study demonstrated that L. r. major may be recorded calling underwater; however, without visual observations during the call events, it is difficult to explain the behaviour of callers. [ABSTRACT FROM AUTHOR]

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Increasing array gains is one of the keys to improving underwater targets' detection capabilities. This paper presents a high-gain approach for a vector hydrophone vertical array (VHVA) that combines white noise gain constraint (WNGC) with vector joint processing to preserve strong robustness and provide noticeable gains. Firstly, this approach treats the VHVA as four independent sub-arrays and achieves sub-array supergains by decorrelating noise using WNGC. The beam outputs of the four sub-arrays are then equated to a single-vector hydrophone, the combination gain of which is obtained by leveraging the strong signal correlation and the weak noise correlation between the sound pressure and the particle velocity. Lastly, the sub-array supergain and combination gain are superposed to provide the spatial gain of the VHVA. It is also summarized that low-frequency signals, coherent noise, accurate elevation-angle estimation, and stable phase differences are required for the VHVA to achieve supergain. The simulation and sea trial confirm that this approach can effectively boost the array gain. The maximum spatial gain in the experiment was increased by 9 dB at a range twice the sea's depth while operating at a low frequency. This method shows enormous potential for improving the performance of deep-sea target detection. [ABSTRACT FROM AUTHOR]

Utilizing hydrophone arrays for detecting underwater acoustic communication (UWAC) signals leverages spatial information to enhance detection efficiency and expand the perceptual range. This study redefines the task of UWAC signal detection as an object detection problem within the frequency–azimuth (FRAZ) spectrum. Employing Faster R-CNN as a signal detector, the proposed method facilitates the joint prediction of UWAC signals, including estimates of the number of sources, modulation type, frequency band, and direction of arrival (DOA). The proposed method extracts precise frequency and DOA features of the signals without requiring prior knowledge of the number of signals or frequency bands. Instead, it extracts these features jointly during training and applies them to perform joint predictions during testing. Numerical studies demonstrate that the proposed method consistently outperforms existing techniques across all signal-to-noise ratios (SNRs), particularly excelling in low SNRs. It achieves a detection F1 score of 0.96 at an SNR of −15 dB. We further verified its performance under varying modulation types, numbers of sources, grating lobe interference, strong signal interference, and array structure parameters. Furthermore, the practicality and robustness of our approach were evaluated in lake-based UWAC experiments, and the model trained solely on simulated signals performed competitively in the trials. [ABSTRACT FROM AUTHOR]

Background: Ionoacoustics is a promising approach to reduce the range uncertainty in proton therapy. A miniature‐sized optical hydrophone (OH) was used as a measuring device to detect weak ionoacoustic signals with a high signal‐to‐noise ratio in water. However, further development is necessary to prevent wave distortion because of nearby acoustic impedance discontinuities while detection is conducted on the patient's skin. Purpose: A prototype of the probe head attached to an OH was fabricated and the required dimensions were experimentally investigated using a 100‐MeV proton beam from a fixed‐field alternating gradient accelerator and k‐Wave simulations. The beam range of the proton in a tissue‐mimicking phantom was estimated by measuring γ‐waves and spherical ionoacoustic waves with resonant frequency (SPIRE). Methods: Four sizes of probe heads were fabricated from agar blocks for the OH. Using the prototype, the γ‐wave was detected at distal and lateral positions to the Bragg peak on the phantom surface for proton beams delivered at seven positions. For SPIRE, independent measurements were performed at distal on‐ and off‐axis positions. The range positions were estimated by solving the linear equation using the sensitive matrix for the γ‐wave and linear fitting of the correlation curve for SPIRE; they were compared with those measured using a film. Results: The first peak of the γ‐wave was undistorted with the 3 × 3 × 3‐cm3 probe head used at the on‐axis and 3‐cm off‐axis positions. The range positions estimated by the γ‐wave agreed with the film‐based range in the depth direction (the maximum deviation was 0.7 mm), although a 0.6–2.1 mm deviation was observed in the lateral direction. For SPIRE, the deviation was <1 mm for the two measurement positions. Conclusions: The attachment of a relatively small‐sized probe head allowed the OH to measure the beam range on the phantom surface. [ABSTRACT FROM AUTHOR]

This paper investigates a 1.7 mm diameter ultra-weak fiber Bragg grating (UWFBG) hydrophone towed array cable for acoustic direction finding. The mechanism of the underwater acoustic waves received by this integrated-coating sensitizing optical cable is deduced, and it is shown that the amplitude of its response varies with the direction of the sound wave. An anechoic pool experiment is carried out to test the performance of such a hydrophone array. The test array is a selection of six sensing fibers, each of which is coiled into 9 cm diameter fiber ring suspended in the water to receive acoustic signals. An average sensitivity of −141.2 dB re rad/μPa at frequencies from 2.5 kHz to 6.3 kHz was achieved, validating the detection of the azimuth of underwater acoustic waves. The ultra-thin towing cable system, with free structure, high sensitivity, and underwater target-detection capability has demonstrated great potential for future unmanned underwater vehicle (UUV) applications. [ABSTRACT FROM AUTHOR]

Jobos Bay National Estuarine Research Reserve (JBNERR) has flora and fauna adapted to a tropical climate. Within the reserve lies the Aguirre Power Plant Complex, which produces a great deal of noise that could place significant stress on marine life and cover a significant area. To test this hypothesis, underwater sound frequencies were recorded at several points of different proximity to the power plant using a hand-held sound recorder with a hydrophone attachment. Each recording was two minutes in duration and positioned one meter above the ocean floor. Results revealed anthropogenic noise from the power plant is strongly present in the 0.01-200 Hz frequency range in an area up to 1.5 km from the power plant. However, because sound waves travel further in water than in air, this distance could be even greater. Acoustic frequencies from the power plant were not detected across a mangrove barrier located approximately 1.0 kilometers from the power plant. This implies that mangroves may have an unreported noise reduction function which, in this case, mitigates and completely blocks off acoustic frequencies from the power plant. [ABSTRACT FROM AUTHOR]

Copyright of Caspian Journal of Environmental Sciences is the property of University of Guilan & Association of Universities of the Caspian Region States and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The passive estimation of harmonic sound source depth is of great significance for underwater target localization and identification. Passive source depth estimation using a single hydrophone with an unknown seabed geoacoustic property is a crucial challenge. To address this issue, a harmonic sound source depth estimation algorithm, seabed independent depth estimation (SIDE) algorithm, is proposed. This algorithm combines the estimated mode depth functions, modal amplitudes, and the sign of each modal to estimate the sound source depth. The performance of the SIDE algorithm is analyzed by simulations. Results show that the SIDE is insensitive to the initial range of the sound source, the source depth, the hydrophone depth, the source velocity, and the type of the seabed. Finally, the effectiveness of the SIDE algorithm is verified by the SWellEX-96 data. [ABSTRACT FROM AUTHOR]

For a multi-hydrophone synthetic aperture sonar (SAS), the instability of the platform and underwater turbulence easily lead to two-dimensional (2-D) space-variant (SV) motion errors. Such errors can cause serious imaging problems and are very difficult to compensate for. In this study, we propose a 2-D SV motion compensation algorithm for a multi-hydrophone SAS based on sub-beam compensation. The proposed algorithm is implemented using the following four-step process: (1) The motion error of each sub-beam is obtained by substituting the sonar's motion parameters measured in the exact motion error model established in this study. (2) The sub-beam's targets of all targets are compensated for motion error by implementing two-phase multiplications on the raw data of the multiple-hydrophone SAS in the order of hydrophone by hydrophone. (3) The data of the sub-beam's target compensated motion error are extracted from the raw data by utilizing the mapping relationship between the azimuth angle and the Doppler frequency. (4) The imaging result of each sub-beam is obtained by performing a monostatic imaging algorithm on each sub-beam's data and coherently added to obtain high-resolution imaging results. Finally, the validity of the proposed algorithm was tested using simulation and real data. [ABSTRACT FROM AUTHOR]

This study presents the results of three-dimensional (3D) propagation modeling of noise from a transiting bulk carrier vessel. In the simulated scenario, the surface vessel is moving past a bottom-mounted hydrophone system. Sound levels are estimated in decidecade frequency bands as the vessel transits past the hydrophone, and the simulation results are compared against real measured data. The modelling is performed using the program AMPLE, which is based on the wide-angle mode parabolic equation theory for simulating 3D broadband acoustic fields in a shallow sea. The model is used to investigate the effect of 3D phenomena on the surface vessel sound propagation. It is shown that an inaccuracy of the noise simulation associated with the use of a two-dimensional model can be as high as 7–10 dB for certain distances and for frequency bands over which a major part of the source energy is distributed. An approach to the selection of data-adjusted media parameters based on the Bayesian optimization is suggested, and the influence of the various parameters on the sound levels is discussed. [ABSTRACT FROM AUTHOR]

Surface and underwater (S/U) acoustic targets recognition is an important application of passive sonar. It is difficult to distinguish them due to the mixture of underwater target radiation noise and marine environmental noise. In previous studies, although using a single hydrophone was able to identify S/U acoustic targets, there were still a few hydrophones that had poor accuracy. In this paper, S/U acoustic targets recognition using two hydrophones based on Gradient Boosting Decision Tree is proposed, and it is first found out as high as 100% accuracy could be achieved with the implementation of SACLANT 1993 data. The real experimental data are always rare and insufficient. The big training dataset is generated using environmental information by acoustic model named KRAKEN. Simulation and experimental data used in the model are heterogeneous, and the differences between these two kinds of data are assimilated by using vertical linear array feature extraction method. The model realizes the recognition of S/U acoustic targets based on channel information besides source spectrum information. By using the combination of two hydrophones, the surface and underwater targets recognition accuracy reached 1 and 0.9384, while they are only 0.4715 and 0.5620 using a single hydrophone, respectively. [ABSTRACT FROM AUTHOR]

This paper delves into enhancing the performance of ScAlN-based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) through the implementation of Polydimethylsiloxane (PDMS) acoustic lenses. The PMUT, encapsulated in PDMS, underwent thorough characterization through the utilization of an industry-standard hydrophone calibration instrument. The experimental results showed that the ScAlN-based PMUT with the PDMS lenses achieved an impressive sensitivity of −160 dB (re: 1 V/μPa), an improvement of more than 8 dB compared to the PMUT with an equivalent PDMS film. There was a noticeable improvement in the −3 dB main lobe width within the frequency response when comparing the PMUT with PDMS encapsulation, both with and without lenses. The successful fabrication of high-performance PDMS lenses proved instrumental in significantly boosting the sensitivity of the PMUT. Comprehensive performance evaluations underscored that the designed PMUT in this investigation surpassed its counterparts reported in the literature and commercially available transducers. This encouraging outcome emphasizes its substantial potential for commercial applications. [ABSTRACT FROM AUTHOR]

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The small size, high sensitivity, and immunity to electromagnetic interference of fibre-optic ultrasound sensors make them highly attractive for applications in biomedical imaging and metrology. Typically, such sensors rely on optically resonant structures, such as Fabry–Perot cavities, that require elaborate fabrication techniques. Here, an alternative fibre-optic ultrasound sensor is presented that comprises a simple deformable and reflective structure that was deposited using simple dip-coating. Interrogation with a laser Doppler vibrometer demonstrated how this sensor achieved a sensitivity, signal-to-noise ratio, and noise-equivalent pressure that outperformed piezoelectric hydrophones, whilst offering a highly miniature form factor, turn-key operation, and simple fabrication. [ABSTRACT FROM AUTHOR]