Underwater Acoustic Signals Research Articles

Statistics of near surface underwater scattered sound including wave induced Doppler

The interaction of underwater sound with the ocean surface is explored. Analytic expressions for the Doppler shift and Doppler spread of surface reflected signals are developed. Statistical models for surface scattered intensity, arrival time, and Doppler fluctuations are developed in relation to wave shape, transducer position, and transmission frequency. Measurements from two experiments are considered. Data collected from AUTEC explore surface scattering effects in the frequency regime of 8 kHz–10 kHz, while data collected in a variable speed wind wave channel at Scripps Institution of Oceanography explore scattering statistics in the 200 kHz–400 kHz (VHF) frequency regime. Physics based analytic expressions for the equations of motion of specular reflection points (SRPs) along a time-evolving wave surface are derived. The time-varying Doppler shift of VHF underwater acoustic signals is attributed to SRP motion associated with surface wave propagation. Model predicted values are compared to experimenta...

Visualizing detecting low-frequency underwater acoustic signals by means of optical diffraction.

A novel and simple technique based on the light diffraction effect for visualization of low-frequency underwater acoustic waves (LFUAWs) in real time has been developed in this paper. A cylindrical object has been put on the surface of the water. A low-frequency underwater longitudinal wave can be generated into a water surface transversal capillary wave around the cylinder by our technique. Modulating the phase of a laser beam reflected from a water surface by surface acoustic waves (SAWs) realizes the acousto-optic effect. Then, a steady and visible diffraction pattern is experimentally observed. A physical model of the SAW is established to verify the feasibility of our technique. An analytical expression of wavelength, wave amplitude, and excitation frequency has been derived to study the physical properties of LFUAWs, and it explains the experimental phenomenon very well. As a result, the technique is effective, easy, and practical for visualizing LFUAWs and has significance for applications.

Noise reduction method of ship radiated noise with ensemble empirical mode decomposition of adaptive noise

Ensemble empirical mode decomposition method (EEMD) is important improvement of the empirical mode decomposition (EMD), but it still leaves some annoying difficulties unresolved, such as large computational cost and reconstruction error. To solve above problems of the EEMD, a new method named EEMD of adaptive noise (EEMDAN) is proposed, which can obtain accurate time-frequency distribution of the original signal. In addition, aiming at the non-linear, non-stationary and non-Gaussian characteristics of underwater acoustic signal, a noise reduction method based on the EEMDAN is also proposed. Each order intrinsic mode function (IMF) can be obtained by the EEMDAN for noisy Lorenz signal and three different types of real ship radiated noises. The components of the signal and noise can be adaptively determined by IMF correlation coefficient based on energy density and average cycle. The results show that the method is effective and a very clean signal can be obtained.

Fractional 푸리에 변환을 이용한 능동소나 표적탐지

Many studies in detection and classification of the targets in the underwater environments have been conducted for military purposes, as well as for non-military purpose. Due to the complicated characteristics of underwater acoustic signal reflecting multipath environments and spatio-temporal varying characteristics, active sonar target detection technique has been considered as a difficult technique. In this paper, we describe the basic concept of Fractional Fourier transform and optimal transform order. Then we analyze the relationship between time-frequency characteristics of an LFM signal and its spectrum using Fractional Fourier transform. Based on the analysis results, we present active sonar target detection method. To verify the performance of proposed methods, we compared the results with conventional FFT-based matched filter. The experimental results demonstrate the superiority of the proposed method compared to the conventional method in the aspect of AUC(Area Under the ROC Curve).

Mach-Zehnder interferometric photonic crystal fiber for low acoustic frequency detections

Low frequency under-water acoustic signal detections are challenging, especially for marine applications. A Mach-Zehnder interferometric hydrophone is demonstrated using polarization-maintaining photonic-crystal-fiber (PM-PCF), spliced between two single-mode-fibers, operated at 1550 nm source. These data are compared with standard hydrophone, single-mode and multimode fiber. The PM-PCF sensor shows the highest response with a power shift (2.32 dBm) and a wavelength shift (392.8 pm) at 200 Hz. High birefringence values and the effect of the imparted acoustic pressure on this fiber, introducing the difference between the fast and slow axis changes, owing to the phase change in the propagation waves, demonstrate the strain-optic properties of the sensor.

Predicting Modeling Method of Ship Radiated Noise Based on Genetic Algorithm

Because the forming mechanism of underwater acoustic signal is complex, it is difficult to establish the accurate predicting model. In this paper, we propose a nonlinear predicting modeling method of ship radiated noise based on genetic algorithm. Three types of ship radiated noise are taken as real underwater acoustic signal. First of all, a basic model framework is chosen. Secondly, each possible model is done with genetic coding. Thirdly, model evaluation standard is established. Fourthly, the operation of genetic algorithm such as crossover, reproduction, and mutation is designed. Finally, a prediction model of real underwater acoustic signal is established by genetic algorithm. By calculating the root mean square error and signal error ratio of underwater acoustic signal predicting model, the satisfactory results are obtained. The results show that the proposed method can establish the accurate predicting model with high prediction accuracy and may play an important role in the further processing of underwater acoustic signal such as noise reduction and feature extraction and classification.

Closed Form Analysis of the Normalized Matched Filter With a Test Case for Detection of Underwater Acoustic Signals

In this paper, closed-form expressions for the performance of the normalized matched filter (NMF) detector are developed specifically for the case of large time-bandwidth product, N. As a test case, the task of detecting underwater acoustic signals is considered. While the matched filter is the most common detector used, the NMF detector is used in cases where the ambient noise is fast time varying and is hard to estimate. While the performance of the NMF has been studied, no closed-form expressions are given for the detection and false alarm probabilities, and the accuracy of the available approximations greatly deteriorates with N. As a result, evaluating the detection threshold from the receiver operating characteristic requires significant, and sometimes untraceable, numerical calculations. This is specifically important for underwater acoustic signals, where due to the low signal-to-noise ratio, N is very large. The analysis performed in this paper solves this problem. The analysis is based on the probability distribution of the NMF to give an exact closed-form (tabulized) expression for the false alarm probability, and a relatively accurate approximation for the probability of detection, both for the large N case. These approximations are found accurate in numerical simulations. Results from an experiment conducted in the Mediterranean sea at the depth of roughly 1000 m validate the analysis.

The Control Packet Collision Avoidance Algorithm for the Underwater Multichannel MAC Protocols via Time-Frequency Masking

Establishing high-speed and reliable underwater acoustic networks among multiunmanned underwater vehicles (UUVs) is basic to realize cooperative and intelligent control among different UUVs. Nevertheless, different from terrestrial network, the propagation speed of the underwater acoustic network is 1500 m/s, which makes the design of the underwater acoustic network MAC protocols a big challenge. In accordance with multichannel MAC protocols, data packets and control packets are transferred through different channels, which lowers the adverse effect of acoustic network and gradually becomes the popular issues of underwater acoustic networks MAC protocol research. In this paper, we proposed a control packet collision avoidance algorithm utilizing time-frequency masking to deal with the control packets collision in the control channel. This algorithm is based on the scarcity of the noncoherent underwater acoustic communication signals, which regards collision avoiding as separation of the mixtures of communication signals from different nodes. We first measure the W-Disjoint Orthogonality of the MFSK signals and the simulation result demonstrates that there exists time-frequency mask which can separate the source signals from the mixture of the communication signals. Then we present a pairwise hydrophones separation system based on deep networks and the location information of the nodes. Consequently, the time-frequency mask can be estimated.

A source range and depth estimation method based on modal dedispersion transform

The wideband source localization is analysed widely in shallow water. It is pointed out that its performance is poor when the number of array elements is few or the ocean environment is uncertain. A method of estimating the range and depth is studied by using a single hydrophone based on the relationship of the horizontal wavenumber difference between two modes with the waveguide invariant for low frequency underwater acoustic pulse signals in a range-independent shallow water waveguide. This localization method estimates the source range by using the rangedispersion two-dimensional（2D) plane focus phenomenon and also the source depth by matching the modal energy. So it can separately estimate the source range and source depth by single hydrophone. First, the signal received on a single hydrophone can be decomposed into a series of modes within the framework of normal mode theory. In order to obtain a better localization performance, the first few order modal dispersion parameters and waveguide invariant are regarded as the unknown parameters. And then the first few order modal dispersion parameters and waveguide invariant can be estimated by comparing the differences between the modal phase velocity calculated by Eq.(8) and that calculated by the Kraken model. Second, using the estimated dispersion parameters and waveguide invariant for dedispersion transform, the amplitudes of each normal mode can achieve maximum values but only when the range of the received signal after dedispersion transform is equal to the range of source. On range-dispersion 2D plane, there appears the sound pressure focus phenomenon, and this phenomenon can be used to estimate the source range. Simulation results from a shallow water Pekeris waveguide show that the time-frequency distribution represents well the dispersion characteristics of the underwater acoustic pulse signal and the dedisperision transform can eliminate this dispersion at the range of source, so that the source range can be estimated. Besides, the first few order modal signals received are clearly separated in time domain after dedispersion transform, and the first few order modal energy can be calculated accurately. So the source depth can be estimated by matching the modal energy. The errors in range estimation and depth estimation are little in simulation. Finally, the data collected from airgun sources during an experiment in the shallow water are used to verify the presented method, and the experimental results obtained using airgun sources on a straight line are shown. The presented method is very significant for estimating the range and depth in shallow water.

Ship-radiated noise feature extraction using multiple kernel graph embedding and auditory model

The analysis of underwater acoustic signals, especially ship-radiated noise received by passive sonar, is of great importance in theelds of defense, military, and scientic research. In this paper, we investigate multiple kernel learning graph embedding using auditory model features in the application of ship-radiated noise feature extraction. We use an auditory model to get auditory model features for each signal sample. In order to have more effective features, iterative multiple kernel learning methods are adopted to conduct dimensionality reduction. Validated by experiments, the proposed method outperforms ordinary kernel-based graph embedding methods. The experiments show that the multiple kernel learning method can automatically choose relatively appropriate kernel combinations in dimensionality reduction for ship-radiated noise using auditory model features. In addition, some worthwhile conclusions can be drawn from our experiments and analysis.

Performance Simulation and Fabrication of PZT Piezoelectric Composite Ring

High-frequency wideband omnidirectional transducer is the development direction of the research of underwater acoustic transducer, PZT piezoelectric composite ring is not only capable of horizontal omnidirectional transmitting and receiving underwater acoustic signal. Meanwhile, it also makes the bandwidth of the transducer is expanded. Using the ANASYS finite element simulation software, the modal simulation of the ring structure of the 2-2 type piezoelectric composite is carried out, and the relationship curve of the bandwidth and the structure size is obtained. Based on the simulation, a design scheme is formed, cutting circular piezoelectric ceramics along the axial direction, there is epoxy resin in the groove. Thus the 2-2 type piezoelectric composite circular tube is formatted. The piezoelectric composite circular tubes suitable for horizontal omnidirectional broadband transducer.

Array gain of conventional beamformer affected by structure of acoustic field in continental slope area

Conventional beamforming (CBF) is an important processing step in underwater array signal processing. Previous researches have shown that the sound field structure as manifested by amplitude nonhomogeneity and wave-front corrugation can reduce the array gain of CBF. The acoustic environment of the continental shelf slope area is very complex. For an underwater acoustic array in this area, the amplitude and phase of the received signals will be distortional seriously. Recently, the acoustic field correlation has been the focus of research on the array gain relations with the underwater acoustic filed. However, the attenuation of acoustic field correlation is not the only factor that induces the array gain to decline, and the analyses of the array gain in the shallow water based on normal-mode model are not applicable to the continental slope area. In this paper, the array gain relations with the structure of acoustic field in continental slop area are investigated based on the theory of underwater acoustic signal propagation. The effects of acoustic field on the signal and noise gains are considered respectively. The analytic expressions of the array gain of CBF in an isotropic noise field are derived from the primal definition of array gain, which indicates that acoustic field correlation and transmission loss in continental slope are the intrinsic factors that affect the array gain of CBF. A horizontal uniform linear array (ULA) with a wide aperture receiving signals from a source in the deep water region is considered in the upslope propagation condition. The RAM program is utilized in the numerical simulations to generate the sound field of this specific environment with given parameters. The array gains, the ATLs and the horizontal longitudinal correlation coefficients of the acoustic field corresponding to three different locations are compared. Conclusions can be drawn as follows. 1) The array gain of CBF is determined by acoustic field correlation and the acoustic average transmission loss (ATL), and its maximum is less than 10lg M as the signal waveform distortion. 2) when the ATLs corresponding to hydrophones at two different receiving locations are similar, the correlation of acoustic filed is higher, and the array gain of CBF is larger. 3) When the ATLs corresponding to hydrophones at two different receiving locations are greatly different, the relation between the array gain of CBF and the acoustic filed correlation is no longer positive. The simulation results verify the array gain of CBF relations with the acoustic filed correlation and the transmission loss in the continental slope area.

AUV Underwater Positioning Algorithm Based on Interactive Assistance of SINS and LBL.

This paper studies an underwater positioning algorithm based on the interactive assistance of a strapdown inertial navigation system (SINS) and LBL, and this algorithm mainly includes an optimal correlation algorithm with aided tracking of an SINS/Doppler velocity log (DVL)/magnetic compass pilot (MCP), a three-dimensional TDOA positioning algorithm of Taylor series expansion and a multi-sensor information fusion algorithm. The final simulation results show that compared to traditional underwater positioning algorithms, this scheme can not only directly correct accumulative errors caused by a dead reckoning algorithm, but also solves the problem of ambiguous correlation peaks caused by multipath transmission of underwater acoustic signals. The proposed method can calibrate the accumulative error of the AUV position more directly and effectively, which prolongs the underwater operating duration of the AUV.

Hopper WDM을 이용한 FBG(Fiber Bragg Grating) 하이드로폰(Hydrophone)의 다중점신호검출 및 지향성 연구

In the using of FBG(Fiber Bragg Grating) developed in home land, we designed and manufactured united FBG acoustic transducers the first in Korea. they are being applied to multi-point signal detection of FBG Hydrophone used Hopper WDM(national patent NO 10-1502954) in the underwater. On united FBG transducers manufactured, we made an demonstrated on respective frequency response peculiarities in the underwater and analyzed the special characters. As the experimental result on frequency response peculiarities, we made it possible underwater acoustic detection on united FBG acoustic transducers type to maximum 30Hz~2.5KHz. it's the optimum conditions of 1.2KHz frequency in detection. And for the purpose of realization on multi-point signal detection on wide scope in the underwater, in the using of WDM(Wavelength Division Multiplexing) method and passive band-pass filter system, established arrays system and succeeded in multi-point underwater acoustic signal detection to the frequency 200Hz~1.3KHz out of the two united type FBG transducers. Additionally, it would be possible directivity detection for the object of its source as the intensity of detection signal varies with the sound source's direction and angle. From now on we prepared a new moment on the practical use study on FBG hydrophone in the future.

Bio-inspired piezoelectric artificial hair cell sensor fabricated by powder injection molding

A piezoelectric artificial hair cell sensor was fabricated by the powder injection molding process in order to make an acoustic vector hydrophone. The entire process of powder injection molding was developed and optimized for PMN–PZT ceramic powder. The artificial hair cell sensor, which consists of high aspect ratio hair cell and three rectangular mechanoreceptors, was precisely fabricated through the developed powder injection molding process. The density and the dielectric property of the fabricated sensor shows 98% of the theoretical density and 85% of reference dielectric property of PMN–PZT ceramic powder. With regard to homogeneity, three rectangular mechanoreceptors have the same dimensions, with 3 μm of tolerance with 8% of deviation of dielectric property. Packaged vector hydrophones measure the underwater acoustic signals from 500 to 800 Hz with −212 dB of sensitivity. Directivity of vector hydrophone was acquired at 600 Hz as analyzing phase differences of electric signals.

Optical fiber distributed acoustic sensing based on the self-interference of Rayleigh backscattering

In order to detect the weak underwater acoustic signal, a Distributed Acoustic Sensing (DAS) scheme based on the self-interference of Rayleigh backscattering is presented. Rayleigh backscattered light which contains a phase change induced by acoustic signal along the sensing fiber which is a standard telecom single-mode fiber is split and fed into an imbalance Michelson interferometer. With the self-interference of two Rayleigh backscattered beams, the phase change is amplified theoretically compared with phase-sensitive OTDR. We designed an experiment to prove the scheme, and successfully restored the acoustic information, meanwhile, the DAS system has preliminary realized around the acoustic phase sensitivity of −151dB (re rad/μPa) at 600Hz, and the minimum detectable acoustic pressure of 6Pa in the experiment.

The asymmetric distribution of diffraction field with different frequencies of underwater acoustic signal

A measurement system is developed to detect the low-frequency underwater acoustic signal. The clear and highly stable diffraction pattern is observed experimentally when the laser beam illuminates on the liquid surface which is stimulated by the underwater acoustic signal, the diffraction pattern is asymmetric distribution. The expression of the diffraction pattern intensity was derived theoretically. The asymmetry distribution of the location and intensity of the diffraction pattern were explained with the laser oblique incident on the liquid surface, and the symmetric distribution of the diffraction pattern was explained with the laser vertical incident on the liquid surface as well. It is consistent between theory and experiment.

Study of Different Denoising Methods for Underwater Acoustic Signal

Marine Engineering faces certain challenges in recent times due to the prevalence of ambient conditions caused by imbalance in the ecosystem. Underwater ambient noise is primarily a background noise, which is a function of time, location and depth. It is of prime importance to detect the signals such as the sound of a submarine or an echo from a target, surpassing and surmounting this ambient noise. In the absence of the sound from ships and marine life, underwater ambient noise levels are dependent mainly on wind speeds at frequencies between 500 Hz and 50 KHz (Urick, 1984). Since there is a possibility of signal and noise present in the same frequency, it becomes indispensable to find out a suitable algorithm to perform denoising. In this paper the functioning of different denoising methods: wavelet, Empirical Mode Decomposition (EMD) in time domain, Ensemble Empirical Mode Decomposition (EEMD) and frequency domain based EMD are studied and the results are compared. The proposed frequency domain algorithm produced better results in the frequency ranging from 50 Hz to 25 KHz, with less signal error-an encouraging result. This work is calibrated through a comparison made with the existing methods and the outcomes obtained are found to be better than the existing algorithms like wavelet, EMD in time domain, etc.

Minimizing the Total Energy Consumption in Multi-hop UWASNs

This paper investigates the total energy consumption in multi-hop underwater acoustic sensor networks (UWASNs) for a given target signal to noise ratio (SNR) requirement. Specifically, our aim is to minimize the energy consumption along the route between source and destination and to find the optimal hop distance that result in minimum energy consumption, by taking into account the propagation characteristics of sound signals through the underwater acoustic medium. The proposed study will form the basis for the design of energy efficient routing protocols that select minimum energy route in UWASNs. The impact of various characteristics of underwater acoustic signal propagation such as attenuation, noise, and the dependence of usable bandwidth and transmit power on distance, are considered for the energy consumption analysis. Further, analysis is carried out for both shallow and deep water scenarios under the assumption that each node can adjust its transmission power for a link so that the signal reaches the destination node, satisfying a target received SNR. We observe that, a linear equidistant network consumes minimum energy for both shallow as well as deep water scenarios.

Underwater acoustic signals induced by intense ultrashort laser pulse.

Acoustic signals generated in water by terawatt (TW) laser pulses undergoing filamentation are studied. The acoustic signal has a very broad spectrum, spanning from 0.1 to 10 MHz and is confined in the plane perpendicular to the laser direction. Such a source appears to be promising for the development of remote laser based acoustic applications.