Single Hydrophone Research Articles

Study on passive location method of shallow water acoustic source with single hydrophone

In order to meet the needs of target detection in shallow water with concealed and low energy consumption platform, the Bayesian estimation theory was applied to underwater acoustic location. The underwater acoustic location model was established based on probability density function as the description of sound source state, so as to overcome the problems of unstable shallow water environment and mismatching of sound field model. Histogram filtering method is used to solve the integral solution in the process of posterior probability estimation of sound source state. The hierarchical grid histogram filtering method is proposed for the first time, which effectively improves the efficiency of histogram filtering iterative algorithm. The measured data and simulation results of SWelleX-96 show that the depth positioning accuracy can reach 35 m and the distance positioning accuracy can reach 0.69 km within the range of 200 m deep and 10 km long in shallow water environment, and the efficiency of the algorithm can be improved by N1/2 times.

Resolution of matched field processing for a single hydrophone in a rigid waveguide.

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.

Motion parameter estimation of AUV based on underwater acoustic Doppler frequency measured by single hydrophone

This paper describes the use of a single hydrophone to estimate the motion parameters of an autonomous underwater vehicle (AUV) from the underwater acoustic signal excited by its propulsion motor. First, the frequency range of the hydroacoustic signal radiated by the AUV motor is determined, and a detection and recognition model is designed. In the case of uniform linear motion of the AUV, the geometric relationship between the Doppler frequency shift curve of the sound source is derived and the motion model of the sound source and sound line propagation is established. An estimation algorithm for the motion parameters of multiple AUVs based on data from a single hydrophone is derived. Then, for Doppler underwater acoustic signals disturbed by independent identically distributed noise with an arbitrary probability distribution, a cumulative phase difference power amplification instantaneous frequency estimation method is proposed. This method is based on the sum of multiple logarithmic functions. Finally, the effectiveness and accuracy of the algorithm in estimating the motion parameters of multiple AUVs are verified through simulations and experiments.

Enhancing cross correlations of ocean ambient noise in the time domain based on random matrix theory.

Cross correlations of diffuse noise can be utilized to recover the time domain Green's function (TDGF) between two points. This principle allows for a variety of practical applications, such as seismic tomography, ocean thermometry, passive localization, etc. However, in the real ocean environment, loud interference noise sources usually bias the travel time estimates of the TDGF or result in poor recovery quality. To deal with this issue, a diffuse noise reconstruction approach is proposed to eliminate the influence of the strong interference noise by utilizing the time domain statistical property of ocean ambient noise recorded on single hydrophones with the help of random matrix theory. Simulation and experimental data analysis indicate that this algorithm can effectively extract the diffuse noise component from the ocean ambient noise field and retrieve the TDGF with a higher signal-to-noise ratio when coherent accumulation of cross correlations of the reconstructed diffuse noise is performed.

An end-to-end deep learning approach for joint detection, source localization and environmental characterization using a single hydrophone in shallow water

Environmental characterization of underwater environments is crucial for modeling acoustic propagation in the ocean, which in turn enables underwater applications such as performing environmental impact studies on the effect of ocean noise on marine life, evaluating sonar performance and more. In this work, the aim is to automate and improve run-time performance of environmental characterization, compared to classical methods which employ high-cost computational schemes and sometimes require manual inputs from a skilled operator. To do so, we use 1D Convolutional Neural Networks (1D-CNN), a type of Deep Learning (DL) model, to acoustically characterize the underwater environment using unprocessed pressure time-series recorded on a single hydrophone. We notably propose an end-to-end approach to detect, classify and localize acoustic sources along with estimating environmental parameters using a single DL model. The experimental data used for testing the resulting 1D-CNN models are signals that were generated by navy explosives (SUS charges) deployed during the Seabed Characterization Experiment performed in the New England Mud-patch off the coast of Massachusetts.

Research on DOA estimation method of single MEMS vector hydrophone based on pulse signal

With the rapid development and wide application of Micro-Electro-Mechanical System (MEMS) vector hydrophones, it is of higher requirement for the estimation method of direction of arrival (DOA) for a single vector hydrophone in complex environments. Although many classical methods for DOA estimation have been proposed in this field, the DOA estimation method in complex environments, such as multipath effects and reverberation, still needs to be further studied. When the target DOA is estimated in the environment with reflected waves, certain errors will be caused due to the reflection provided that the continuous wave method is used. Moreover, the influence of the reflected wave can be decreased once the pulse wave method is used, but it will low the accuracy due to the poor Signal to noise ratio (SNR) problem simultaneously. For that reason, a solution method for DOA estimation using pulsed waves in a reflective environment has been proposed in this paper. The detailed arrangements of this paper are as follows: firstly, the orientation error caused by the low SNR of the pulsed waves was processed by the segmentation and extraction of the pulsed waves; secondly, the effectiveness of the proposed method was tested by experiments and made a DOA estimation error comparison with the classic continuous wave method; finally, the experimental results showed that when MEMS vector hydrophone DOA was estimated in the reflection environment, the estimation error caused by the reflected wave could be effectively reduced by the method proposed in this paper. A solution method for DOA estimation using pulsed waves in a reflective environment has been proposed in this paper. • A solution method for DOA estimation using pulsed waves in a reflective environment has been proposed in this paper. • The orientation error caused by the low SNR was processed by the segmentation and extraction of the pulsed waves. • The effectiveness of the proposed method was tested by experiments and made a comparison with the continuous wave method.

Simultaneous detection and ranging of baleen whale impulsive vocalizations using a temporal convolutional network

In shallow-water environments, low-frequency acoustic signals exhibit dispersive propagation due to interactions with the sea surface and seabed. The received signal can then be modeled as a set of propagating modes. Single-hydrophone modal dispersion has been used to range baleen whale vocalizations and estimate shallow-water geoacoustic properties. However, these algorithms require preliminary signal detection and human labor to estimate the modal dispersion. Here, we apply a temporal convolutional network (TCN) to time-frequency representations of baleen whale gunshots (impulsive calls) to simultaneously detect and range them in large single-hydrophone passive acoustic monitoring datasets. The TCN jointly learns ranging and detection by training using both synthetic gunshots simulated across multiple environments/ranges and experimental noise. The synthetic data is informed by only the experimental dataset’s water column depth, sound speed, and density, while other waveguide parameters vary within empirically observed bounds. The method is applied to an experimental North Pacific right whale dataset collected in the Bering Sea using a single hydrophone. To evaluate model performance, 50 calls are manually ranged using a state-of-the-art physics-based inversion method. The TCN closely matches the physics-based range estimations and detects dispersive gunshots among noise-only examples with high precision and recall. [Work supported by the ONR].

Standing wave tube for the calibration of acoustic vector sensors

Acoustic vector sensors are useful in a variety of applications as they provide directional information for ambient noise by sensing the acoustic particle motion in addition to the acoustic pressure. Traditionally, the motion sensor is an accelerometer that is calibrated separately from the associated hydrophone. There are certain advantages that can be realized by calibrating the accelerometer and hydrophone concurrently in a standing wave tube at low frequencies. First, since the pressure and acceleration are simply related in this environment both sensors can be calibrated against a single reference hydrophone. Second, the vector sensor can be calibrated along with the suspension that will be used to mount it thereby taking into account any effects of the suspension’s dynamics. Third, the vector sensor is calibrated to the fluid acceleration rather than its own acceleration thereby accounting for any mismatch in its density relative to the fluid as well as the suspension dynamics. And fourth, the phase response of the acceleration output relative to the pressure output is measured in the calibration. This technique was implemented using a travelling wave tube that was developed for other applications and found to be accurate and convenient.

Determining the speed dependent source level of a snowmobile traveling on sea-ice

As part of the Sustainable Nunatsiavut Futures project, a field experiment to determine the acoustic properties and underwater radiated sound level of a snowmobile was designed and executed. The fieldwork consists of lowering acoustic recorders under the sea ice and driving a snowmobile with a known position and velocity to evaluate its speed-dependent source level. This experiment is the first step toward collaborative Dalhousie and community research on underwater sound as it relates to the marine habitat, human use of the ocean, and sea-ice in Nunatsiavut. Due to COVID-19, the planning stages were coordinated virtually, and the fieldwork in Nunatsiavut was conducted by local Inuit Research Coordinators (IRCs), while a twin Dalhousie-led experiment was conducted in Caraquet, New Brunswick. A single hydrophone sensor was used in Nunatsiavut, and a vertical array of hydrophones was used in Caraquet to obtain underwater sound data from a moving snowmobile. Skidoo specifications for each site were recorded as well as sea-ice thickness, temperature, salinity, and sound-speed data were collected. Spectrograms of skidoos traveling at different speeds were computed. Comparisons between received levels at different velocities, sites, and ranges are shown, and the impact of sea ice and snowmobile specifications on received levels are discussed.

Evidence of 3D effects for along shelf acoustic propagation during SBCEX21

The 2021 Seabed Characterization Experiment (SBCEX21) was performed on the New England Shelf Break (NESB) in May 2021 with the main objective of characterizing the NESB sediment geoacoustic properties. In this talk, we focus on low-frequency propagation (f<100 Hz) along the 200 m isobath line. Time-frequency dispersion of normal modes is estimated using a SUS charge signal recorded on a distant single hydrophone TOSSIT system. Geoacoustic inversion is performed, but two-dimensional (2D) acoustic propagation models fail to capture the observed behavior of higher order acoustic modes, and predict much shorter travel times than are seen in the data. By introducing a three-dimensional (3D) model environment, both parabolic equation and modal ray calculations confirm that the gradual shelf slope has a nontrivial influence on modal travel times. This comparison between 2D and 3D simulations of SBCEX21 acoustics and experimental data emphasizes the importance of 3D effects from sloped bathymetry on understanding propagation in a shelfbreak environment. These effects will need to be accounted for when doing geoacoustic inversion of SBCEX21 along-shelf low-frequency data.

Characterizing the steering performance of a diagnostic-therapeutic ultrasound array using measured and synthesized holograms

Acoustic holography is frequently used for the characterization of fields generated by ultrasound transducers. For arrays with electronic focusing and beam steering, separate holograms are needed to represent the 3D field for each combination of array parameters. In this paper, we show that holograms for the field generated by each individual element in an ultrasound array can be recorded in a single hydrophone scan, by interleaving a series of excitations at each measurement location in which each element is driven separately. Such holograms were recorded for a 64-element diagnostic-therapeutic linear array with a nominal focal length of 50 mm and pitch of 0.8 mm, which is smaller than the wavelength at the operating frequency of 1.05 MHz. The resulting holograms reveal aspects of crosstalk and variations between array elements. By summing the elemental holograms with the appropriate phase shifts, holograms are synthesized representing source conditions for cases where the entire array is used to generate different beam configurations, with focal lengths between 35 mm and 60 mm, and steering angles of up to 20°. These synthetic holograms are shown to accurately characterize non-ideal steering behavior of the transducer, confirmed through direct hydrophone measurements. [Work supported by NIH grants R01EB023910 and R01EB025187.]

Parametermeasurement of aircraft-radiated noise from a single acoustic sensor node in three-dimensional space

A line spectrum presents the form of a narrow-band time-varying signal due to Doppler effect when the single hydrophone node observes flight-radiated noise. The modulation law of the time-varying signal contains a large number of feature information of moving targets, which can be used for detection and classification. This paper studies the possibility of using instantaneous frequency measurements from the hydrophone node to improve the precision of the flight parameter estimates when the source spectrum contains a harmonic line of constant frequency. First of all, we build up and analyze the underwater sound field excited by the aircraft using the ray theory model; then the Doppler shift in the two isospeed media, which is caused by the aircraft, is established; finally, a robust time–frequency transform describes the time–frequency distribution of the received signal, and a geometric approach solves the flying parameters.

A wave glider-based, towed hydrophone array system for autonomous, real-time, passive acoustic marine mammal monitoring.

An autonomous surface vehicle known as a wave glider, instrumented with a low-power towed hydrophone array and embedded digital signal processor, is demonstrated as a viable low-noise system for the passive acoustic monitoring of marine mammals. Other key design elements include high spatial resolution beamforming on a 32-channel towed hydrophone array, deep array deployment depth, vertical motion isolation, and bandwidth-efficient real-time acoustic data transmission. Using at-sea data collected during a simultaneous deployment of three wave glider-based acoustic detection systems near Stellwagen Bank National Marine Sanctuary in September 2019, the capability of a low-frequency towed hydrophone array to spatially reject noise and to resolve baleen whale vocalizations from anthropogenic acoustic clutter is demonstrated. In particular, mean measured array gain of 15.3 dB at the aperture design frequency results in a post-beamformer signal-to-noise ratio that significantly exceeds that of a single hydrophone. Further, it is shown that with overlapping detections on multiple collaborating systems, precise localization of vocalizing individuals is achievable at long ranges. Last, model predictions showing a 4× detection range, or 16× area coverage, advantage of a 32-channel towed array over a single hydrophone against the North Atlantic right whale upcall are presented for the continental shelf environment south of Martha's Vineyard.

Maximum likelihood separation of anthropogenic and wind-generated underwater noise.

A method is presented for simultaneous estimation of the probability distributions of both anthropogenic and wind-generated underwater noise power spectral density using only acoustic data recorded with a single hydrophone. Probability density models for both noise sources are suggested, and the model parameters are estimated using the method of maximum likelihood. A generic mixture model is utilized to model a time invariant anthropogenic noise distribution. Wind-generated noise is assumed normally distributed with a wind speed-dependent mean. The mean is then modeled as an affine linear function of the wind-generated noise level at a reference frequency, selected in a frequency range where the anthropogenic noise is less dominant. The method was used to successfully estimate the wind-generated noise spectra from ambient noise recordings collected at two locations in the southern Baltic Sea. At the North location, 3 km from the nearest shipping lane, the ship noise surpasses the wind-generated noise almost 100% of the time in the frequency band 63-400 Hz during summer for wind speed 7 m/s. At the South location, 14 km to the nearest shipping lane, the ship noise dominance is lower but still 40%-90% in the same frequencies and wind speed.

A fast inversion method for ocean parameters based on dispersion curves with a single hydrophone

A fast inversion method for ocean parameters based on dispersion curves with a single hydrophone

Signal detection method using a single vector hydrophone in ocean acoustics.

This paper focuses on the problem of transient signal detection using a single vector hydrophone in a horizontal isotropic acoustic field. The covariance matrix of the three sensor output quantities is analyzed in terms of its trace and determinant principal invariants, and the mathematical relationship between the signal-to-noise ratio and these invariants is established. Both the signal power and the ambient-noise power can be accurately estimated directly from the covariance matrix of the received data, and the signal-to-noise ratio can further be obtained. A signal power detector is proposed based on the theoretical analysis, and simulation results show that (i) it can detect signals with low signal-to-noise ratio and (ii) its performance is greatly improved compared with that of an energy detector under the condition of a nonstationary ambient-noise field. An experiment was performed to verify the theoretical analysis and the conclusions of the numerical simulation, and the data-processing results show that this method has good applicability in signal detection.

Single Hydrophone Passive Source Range Estimation Using Phase-Matched Filter

Algorithms working in mode space instead of directly matching the received complex sound pressure were developed to improve computational efficiency and robustness, but these algorithms may be inconvenient to apply in practice because manual operations are often inevitable when performing modal filtering. Based on a phase-matched filter, an imperfect matching scheme named the modal phase based matched impulse response (MP-MIR) is proposed to estimate the source range rapidly and conveniently with a single hydrophone. The field to be matched is still the received complex sound pressure. The replica field is a sum of several “phase” modes, which can be efficiently and conveniently synthesized merely with the horizontal wavenumbers of normal modes and the source–receiver range. The effectiveness of the proposed MP-MIR was demonstrated in localizing 84 emissions along a weakly range-dependent track at ranges of 2.54–20 km in the South China Sea. Although it was found, from cross-correlation coefficients, that the received signals showed strong variation even between adjacent emissions, MP-MIR outperformed the classical matched impulse response (MIR) with a lower standard deviation in most cases, demonstrating good robustness and potential for practical applications.

Research on passive localization method of shallow water acoustic source with single hydrophone based on hierarchical grid histogram filtering

An acoustic field model in the form of a probability density function is established to solve the problem of environmental instability in shallow water. A Bayesian underwater acoustic localization model with the state vector of the acoustic source as a posteriori probability is generated for the purpose of trading time for space in an iterative form and realizing localization of a moving source with a single hydrophone. A hierarchical grid histogram filtering algorithm is proposed, which solves the integral problem in the process of Bayesian filtering and improves the efficiency of the histogram filtering algorithm greatly. The SWellEx-96 experimental results show that in the range of 200 m * 10 km, the relative error of depth positioning is controlled at 12%, the relative error of distance positioning is controlled at 7%, and the efficiency of the algorithm is improved by N1/2 times where N is the number of grids of the histogram filter. The method proposed in this paper is suitable for concealed and low energy consumption platforms in shallow water.

Multihydrophone Fusion Network for Modulation Recognition.

Deep learning (DL)-based modulation recognition methods of underwater acoustic communication signals are mostly applied to a single hydrophone reception scenario. In this paper, we propose a novel end-to-end multihydrophone fusion network (MHFNet) for multisensory reception scenarios. MHFNet consists of a feature extraction module and a fusion module. The feature extraction module extracts the features of the signals received by the multiple hydrophones. Then, through the neural network, the fusion module fuses and classifies the features of the multiple signals. MHFNet takes full advantage of neural networks and multihydrophone reception to effectively fuse signal features for realizing improved modulation recognition performance. Experimental results on simulation and practical data show that MHFNet is superior to other fusion methods. The classification accuracy is improved by about 16%.

Resolution of matched field processing for a single hydrophone in a rigid waveguide

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, we derive 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 power spectral density (PSD) are available, such as 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, we argue that this ambiguity analysis also gives insights into real ocean waveguide localization characteristics under appropriate conditions, and show numerical simulations of matched field localization ambiguity surfaces for some realistic shallow-water Pekeris environments.