Hydroacoustic Signals Research Articles

A hydroacoustic system that radiates at frequencies of 19−26 Hz

A radiating hydroacoustic system intended to generate harmonic and phase-shifted hydroacoustic signals in the frequency band of 1 Hz with a center frequency in the range of 19−26 Hz is described. The maximum change in the radiator volume may be as large as 0.0123 m3, which corresponds to a radiated acoustic power of 1000 W at a frequency of 20 Hz in the boundless water space. The prospects of using the system for carrying out research are demonstrated via the results of its testing on the shelf of the Sea of Japan.

Global acoustic propagation and the link between hydroacoustics and infrasound

The ocean is nearly transparent for acoustic propagation at low frequencies, leading to the detection of signals (seismic events, volcanoes and man-made signals) at distances as large as the ocean basin. When the ocean depth approaches the acoustic wavelength (~ 1500m for 1 Hz energy) the potential for conversion of energy from ocean acoustic propagation to atmospheric infrasonic propagation exists. This was observed in an earthquake off the coast of Australia (Evers et al. GRL 2014) energy was observed as seismic waves, hydro-acoustic waves and then infrasound waves, the latter two on the International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization. In this paper, global scale hydro-acoustic propagation modeling from earthquakes and volcanoes will be presented with an emphasis on the locations where conversion to atmospheric propagation will is possible. Recent observations at the Aloha Cables Observatory (Butler JASA 2016) indicate the possibility of a loss of energy from 1-5 Hz as hydro-acoustic signals propagate over the Oahu-Kauai ridge (the Kauai “Keyhole”). Hydro-acoustic and infrasound modeling of this event will be presented.The ocean is nearly transparent for acoustic propagation at low frequencies, leading to the detection of signals (seismic events, volcanoes and man-made signals) at distances as large as the ocean basin. When the ocean depth approaches the acoustic wavelength (~ 1500m for 1 Hz energy) the potential for conversion of energy from ocean acoustic propagation to atmospheric infrasonic propagation exists. This was observed in an earthquake off the coast of Australia (Evers et al. GRL 2014) energy was observed as seismic waves, hydro-acoustic waves and then infrasound waves, the latter two on the International Monitoring System (IMS) of the Comprehensive Test Ban Treaty Organization. In this paper, global scale hydro-acoustic propagation modeling from earthquakes and volcanoes will be presented with an emphasis on the locations where conversion to atmospheric propagation will is possible. Recent observations at the Aloha Cables Observatory (Butler JASA 2016) indicate the possibility of a loss of energy from 1-5 ...

The comparative efficiency of classical and fast projection algorithms in the resolution of weak hydroacoustic signals

The relationships for optimizing a selective estimate of the correlation matrix of classical (initial and modified) and fast projection algorithms in a complex noise situation were determined. Model investigations on the comparison of the resolution of classical optimized algorithms with the characteristics of two variants of fast projection algorithms were performed. The algorithms were compared using the criterion of a decrease in the time and reduction of the angular zone of the loss of a contact with a weak target when it intersects the path of an intense interfering signal. The relationships that correspond to the most economical realization of the fast algorithm were determined.

Algorithms for passive detection of moving vessels in marine environment

ABSTRACTIn this paper, an investigation on the development of a low-cost passive hydroacoustic system for passive detection of moving vessels to counteract possible collision with an unmanned underwater vehicle is presented. The main goal of this paper is to determine if moving vessels generating hydroacoustic signals/signature are present in the space being searched, and if so, to determine the time delay ΔT between two signals (V1(t) and V2(t)) and consequently to estimate the bearing on the source of the hydroacoustic signals, for example, screw propellers of a moving vessel. The acoustic signals V1(t) and V2(t) have been recorded by a two hydrophones mounted in an unmanned underwater vehicle. In practice, signals V1(t) and V2(t) are heavily corrupted by the additional noise. The noise comes from surrounding environment and from the measurement system errors. Moreover, real signals are often unsteady (nonstationary) and random (stochastic). That is why the different methods have been taken under consideration and the received results have been compared. An analysis has been made for time and frequency domain as well. Due to the planned application of the obstacles detection system in the unmanned underwater vehicle, the algorithm had to be feasible for implementation in digital signal processor.

Bathymetric diffraction of basin-scale hydroacoustic signals.

The ocean is nearly transparent to low frequency sound permitting the observation of distant events such as earthquakes or explosions at fully basin scales. For very low frequency the ocean acts as a shallow-water waveguide and lateral variability in bathymetry can lead to out-of-plane effects. In this paper, data from the International Monitoring System of the Comprehensive Test Ban Treaty Organization (CTBTO) is used to present two cases where robustly localized seismic events in locations clearly within the two-dimensional (2-D) shadow of a continent or large island generate T-phase signals that are received on a hydro-acoustic station. A fully three- dimensional parabolic equation model is used to demonstrate that lateral variability of the bathymetry can lead to diffraction, explaining both observations. The implications of this are that the CTBTO network has greater coverage than predicted by 2-D models and that inclusion of diffraction in future processing can improve the automatic global association of hydroacoustic events.

Intermediate Frequency Hydro-acoustic Signal Simulation

Intermediate Frequency Hydro-acoustic Signal Simulation

DEMON-type algorithms for determination of hydro-acoustic signatures of surface ships and of divers

With the project “System for detection, localization, tracking and identification of risk factors for strategic importance in littoral areas”, developed in the National Programme II, the members of the research consortium intend to develop a functional model for a hydroacoustic passive subsystem for determination of acoustic signatures of targets such as fast boats and autonomous divers. This paper presents some of the results obtained in the area of hydroacoustic signal processing by using DEMON-type algorithms (Detection of Envelope Modulation On Noise). For evaluation of the performance of various algorithm variations we have used both audio recordings of the underwater noise generated by ships and divers in real situations and also simulated noises. We have analysed the results of processing these signals using four DEMON algorithm structures as presented in the reference literature and a fifth DEMON algorithm structure proposed by the authors of this paper. The algorithm proposed by the authors generates similar results to those obtained by applying the traditional algorithms but requires less computing resources than those and at the same time it has proven to be more resilient to random noise influence.

Triad resonance between a surface-gravity wave and two high frequency hydro-acoustic waves

A new class of resonant triad in the family of gravity–acoustic waves has been found. I show that a hydro-acoustic wave interacting with a surface-gravity wave may generate a second hydro-acoustic wave. Interestingly, the two acoustic waves propagate in the same direction with similar wavelengths, that are almost double of that of the gravity wave. The evolution of the wave triad amplitudes is periodic and it is derived analytically, in terms of Jacobian elliptic functions and elliptic integrals. The physical importance of this type of triad interactions is the modulation of pertinent hydro-acoustic signals, leading to inaccurate signal perceptions.

Laser adaptive fiber-optic hydrophone

An implementation scheme of the adaptive fiber-optic laser hydrophone with a membrane-type fiber-optic sensor as a sensitive element is proposed and studied. The sensor signal is phase demodulated using an adaptive holographic interferometer whose key element is a dynamic hologram formed in a photorefractive CdTe crystal. The hydrophone is distinguished by high noise immunity and high sensitivity (–117 dB rel. to 1 V/µPa at a frequency of 4.9 kHz) providing stable detection of hydroacoustic signals with an acoustic pressure from 31 dB (rel. to 20 µPa) in the dynamic range to 42 dB (at 9.6 kHz).

Matched field signal processing in underwater sound channels (Review)

The state of the art of matched field hydroacoustic signal processing is described from the viewpoint of estimating the signal parameters in adaptive antenna arrays. The focus is on methods for solving the problem of source localization in an oceanic waveguide under mismatching effects of different nature, caused by disagreement between the received acoustic field and its model. Different approaches to increase the stability of the algorithms for source position estimation are discussed, which allows an increase in their efficiency in natural conditions.

Optimal and adaptive methods of processing hydroacoustic signals (review)

Different methods of optimal and adaptive processing of hydroacoustic signals for multipath propagation and scattering are considered. Advantages and drawbacks of the classical adaptive (Capon, MUSIC, and Johnson) algorithms and “fast” projection algorithms are analyzed for the case of multipath propagation and scattering of strong signals. The classical optimal approaches to detecting multipath signals are presented. A mechanism of controlled normalization of strong signals is proposed to automatically detect weak signals. The results of simulating the operation of different detection algorithms for a linear equidistant array under multipath propagation and scattering are presented. An automatic detector is analyzed, which is based on classical or fast projection algorithms, which estimates the background proceeding from median filtering or the method of bilateral spatial contrast.

Analysis of the effect of various physical and technical factors on the efficiency of adaptive algorithms of processing of hydroacoustic signals

This paper presents results on evaluating the impact of a set of physical and technical factors on the effectiveness of classical and projection fast adaptive algorithms. The factors include the conditions of signal propagation, including multipath; the noise-signal situation; signal fluctuations due to scattering in the medium; the parameters of the receiving antenna, including the amplitude-phase value of element dispersion; and the parameters of the spectral signal analysis at the output of the antenna elements.

Hydroacoustic signals of Antarctic origin detected at ocean-bottom seismic stations off New Zealand

Glacial calving from polar ice sheets is an important indicator of global climate change, and knowledge of ice discharge rates is useful for predicting global sea level variability and deep ocean circulation patterns. Since calving events are difficult to observe in-situ due to the remoteness of polar regions, the remote detection of hydroacoustic signals originating from these events is a useful monitoring tool for climatologists. We have observed hydroacoustic T-phases on an Ocean Bottom Seismic (OBS) network of 30 seismometers and differential pressure gauges that was deployed off the South Island of New Zealand in 2009–2010. These signals are emergent and strongly dispersive, containing most of their energy in the band between 5 and 15 Hz. We estimated backazimuths for events recorded on differential pressure gauges using array beamforming and F-K analysis. Our results suggest that some observed events originate in the vicinity of Ninnis and Mertz glaciers on George V Coast, East Antarctica, in general agreement with epicenters located by prior surface-wave based calving detection studies.

Approximate Filtration of Noise Reflections in Hydroacoustic Signals

A method of approximate filtration of noise reflections is proposed for measurement of the coordinates of an object with a sound emitter moving in an aquatic environment. A passive hydroacoustic detection and ranging system based on a network of hydrophones is used in the measurements. A two-stage approximation algorithm is employed for digital processing of the Doppler hydroacoustic signals from the outputs of the hydrophones. An example illustrating implementation of the filtration method and its error is considered.

Remote hydroacoustic sensing of large icebergs in the southern Indian Ocean: Implications for iceberg monitoring

Hydroacoustic signals generated by drifting icebergs that crack, disintegrate, and collide were identified on two hydrophone arrays in the Indian Ocean. These hydrophone arrays are deployed in the Sound Fixing and Ranging channel, enabling the detection of small sources over ranges of several thousand kilometers due to the low attenuation. Source locations estimated from the signal bearings at the arrays are used to monitor two very large icebergs, C20 and B17B. Spatial and temporal correlation of the location estimates with satellite observations confirm that the icebergs can be hydroacoustically resolved. Hydroacoustic generation rates at both C20 and B17B are highest at times of observed breakup. For C20, which underwent continuous breakup, clusters of events to the southeast of the main iceberg show that hydroacoustic observations can identify trails of icebergs that calved from the main berg whose dimensions are less than that easily resolved by moderate resolution satellite monitoring.

Adaptive resolution of broadband hydroacoustic signals with partially coherent structure

The problem of resolving a weak broadband signal against the background of a strong broadband signal using adaptive superresolution algorithms for signals with distorted coherence is considered. The correlation matrix is estimated using not only time but also frequency accumulation with a differently formed focusing matrix. Imitative simulation has been carried out and the simulation results are analyzed.

Characterizing noise in the global nuclear weapon monitoring system

Under the auspices of the Comprehensive Nuclear‐Test‐Ban Treaty Organization, a worldwide monitoring system designed to detect the illegal testing of nuclear weaponry has been under construction since 1999. The International Monitoring System is composed of a range of sensors, including detectors for hydroacoustic and seismic signals, and when completed, will include 60 infrasound measurement arrays set to detect low‐frequency sound waves produced by an atmospheric nuclear detonation.

Hydroacoustic, infrasonic and seismic monitoring of the submarine eruptive activity and sub-aerial plume generation at South Sarigan, May 2010

Explosive submarine volcanic processes are poorly understood, due to the difficulties associated with both direct observation and continuous monitoring. In this study hydroacoustic, infrasound, and seismic signals recorded during the May 2010 submarine eruption of South Sarigan seamount, Marianas Arc, are used to construct a detailed event chronology. The signals were recorded on stations of the International Monitoring System, which is a component of the verification measures for the Comprehensive Nuclear-Test-Ban Treaty. Numerical hydroacoustic and infrasound propagation modelling confirms that viable propagation paths from the source to receivers exist, and provide traveltimes allowing signals recorded on the different technologies to be associated. The eruption occurred in three stages, separated by three-hour periods of quiescence. 1) A 46h period during which broadband impulsive hydroacoustic signals were generated in clusters lasting between 2 and 13min. 95% of the 7602 identified events could be classified into 4 groups based on their waveform similarity. The time interval between clusters decreased steadily from 80 to 25min during this period. 2) A five-hour period of 10Hz hydroacoustic tremor, interspersed with large-amplitude, broadband signals. Associated infrasound signals were also recorded at this time. 3) An hour-long period of transient broadband events culminated in two large-amplitude hydroacoustic events and one broadband infrasound signal. A speculative interpretation, consistent with the data, suggests that during phase (1) transitions between endogenous dome growth and phreatomagmatic explosions occurred with the magma ascent rate accelerating throughout the period; during phase (2) continuous venting of fragmented magma occurred, and was powerful enough to breach the sea surface. During the climactic phase (3) discrete powerful explosions occurred, and sufficient seawater was vaporised to produce the contemporaneous 12km altitude steam plume.

Assessing the impact of the expansion of the Doppler bandwidth for error estimation phase hydroacoustic (HA) signal

Assessing the impact of the expansion of the Doppler bandwidth for error estimation phase hydroacoustic (HA) signal

A telemetric measurement complex for acoustic and hydrophysical investigations

A hardware-software complex that allows synchronous measurements of hydroacoustic noises and signals, the temperature, and the pressure at a specified point and provides transmission of theses characteristics via a radio channel and their recording in a shore-based analytical center is described. The offshore part of the complex includes a GPS receiver for testing the location during drift. The results of an experimental approbation of the complex during acoustic thermometry of a water area in the Vityaz bay of the Posiet gulf in the Sea of Japan are presented.