Assessment of Arrow-of-Time Metrics for the Characterization of Underwater Explosions (original) (raw)
Related papers
The long-range detection of an accidental underwater explosion
During the Shallow Water 2006 Experiment, SW06, a power supply for seabed-moored oceanographic equipment suffered an accidental explosion. The equipment was located on the New Jersey Shelf, 175 kilometers south-east of New York. Acoustic signals emitted by the explosion were detected by hydrophone sensors that form part of the International Monitoring System (IMS) of the Comprehensive Test-Ban Treaty Organization (CTBTO). The IMS hydrophones were located at Ascension Island, approximately 8,000 kilometers away from the explosion site. The signals received on the IMS hydrophones are described and their arrival times and azimuths compared with theoretical values derived from underwater acoustic propagation modeling. It is shown that the differences between predicted and observed values of arrival time are less than 2 seconds, indicating an error in travel time prediction of 0.04%. Measured azimuths are shown to be within 0.1 degrees of values derived on the assumption great circle pro...
2006
DSTO possesses a data set of sound pressure time series received at a number of ranges from small explosive detonations along a number of tracks in shallow oceans in the Australian region. In recent years, these time series data have been under study by DSTO and Curtin University in relation to the potential impact of underwater explosions on marine fauna, in particular, marine mammals. Past work had shown that the characteristics of waveforms received at medium ranges might be simulated closely if bathymetry and sound speed data were known, and if the seafloor reflectivity was known at relevant frequencies. Sound pressure peaks were, however, over-predicted by the modelling, unless time spreading effects attributed to reflections from non-smooth ocean boundaries were included. This paper reviews this past work and shows the results of more recent analyses in which data along a much greater number of ocean tracks have been studied. It does appear from this analysis of the extended data set that if the sound transmission from an explosive detonation is via bottom bounces, or via surface reflections from a rough surface, the peak level received is considerably less than the value expected from weak shock theory for a single arrival in a uniform ocean of infinite extent. However, if transmission is via surface reflections from a nearly smooth surface, the measured peak level is closer to the theoretical value. This conclusion is illustrated with a presentation of at-sea data and comparison with modelled time series.
2005
The sound pressure time series received at medium ranges from small underwater explosives, known as "SUS" charges, have been under close study in recent years in relation to the potential impact of the use of such devices on marine fauna, in particular, marine mammals. Past work has centred on investigations of time series measured in shallow oceans in the Australian region. Here, at-sea measured data showed, consistently, received peak levels which were considerably less than published weak shock theory would have suggested. This paper shows the results from the analysis of an extended data set, which includes measurements of SUS signals received along a shallow ocean track in an additional ocean region. Further, this paper shows the results of simulations of the time series received along all these tracks. These simulations of received SUS waveforms, carried out at Curtin University, have been obtained by generating an inverse Fourier transform of the product of the oceanic transfer function and the Fourier transform of an input SUS waveform. The oceanic transfer function has been based on the use of the SCOOTER model at low frequencies and a ray model (BELLHOP gaussian beam ray model) at remaining frequencies. By simulating the received time series in this way, reasons for the discrepancies between measured peak data and expectations based on weak shock theory have been investigated and are presented in this paper.
Acoustic characteristics of fish bombing: potential to develop an automated blast detector
Marine Pollution Bulletin, 2003
The use of explosives to catch fish has caused extensive damage to coral reefs throughout Southeast Asia, but the frequency with which they are used is largely unknown. The aim of this work is to develop a detection system capable of distinguishing underwater explosions from background noise, and locating their origin by triangulation. Blast signals have been recorded over a range of distances and the key features that differentiate them from background noise have been determined. For small charges the effective range of such a detector is more than 12 km and may extend up to 50 km depending on the mass of the charges being used. Such a system would help to determine the scale of the problem, identify areas at greatest risk and quantify the effectiveness of management intervention designed to control destructive fishing practices. It may assist with fisheries enforcement in some areas.
T-Wave Detection of Two Underwater Explosions off Hawaii on 13 April 2000
Bulletin of the Seismological Society of America, 2003
We studied two presumed underwater explosions, detonated on 13 April 2000 (approximate times 00:19 and 23:29 coordinated universal time), at a site located approximately 215 km southwest of Oahu, Hawaii, and detected from a combination of T phases recorded at shore-based seismic stations and acoustic waves recorded by hydrophones. The explosions were initially detected by the Polynesian Seismic Network, and a preliminary location obtained in the vicinity of Kauai. With the use of an enlarged dataset, an improved location was obtained, after correcting arrival times for both the influence of the seismic path at the receivers, and the effect of dispersion along the acoustic path. The explosive nature of the source was tested using several criteria: the duration-amplitude discriminant of Talandier and Okal (2001), the variation of spectral amplitude with frequency, the observation of a strong frequency dispersion in the spectrograms, and the identification of a bubble period (0.45 sec) in the cepstra of the signals, which translates into a yield of 275 kg of equivalent TNT for a depth of 50 m. In the context of monitoring the Comprehensive Nuclear Test Ban Treaty, these two explosions provide a perfect opportunity to assess the capabilities of T-phase stations and hydrophones for detection, location, identification, and quantification of these sources. Our study, conducted in the absence of any ground-truth information, stresses the possibility of a powerful synergy between these two types of recording facilities, but also points to several limitations in the performance of certain shore-based seismic stations.
1991
Abstract The authors demonstrate the application of the Wigner-Ville time-frequency distribution, the bispectrum, the time-varying bispectrum, and Gerr's third-order Wigner distribution to some underwater acoustic data. They also demonstrate the merit of including higher-order spectral information when signaturing underwater acoustic sources. It is pointed out that conventional signal analysis procedures do not utilize all the information available in many practical signal analysis problems.
Acoustics, Speech and Signal Processing, IEEE Transactions on, 1990
Signal detection techniques based on time-frequency signal analysis with the Wigner-Ville distribution (WVD) and the cross Wigner-Ville distribution (XWVD) are presented. These techniques are shown to provide high-resolution signal characterization in a time-frequency space, and good noise rejection performance. This type of detection is applied to the signaturing, detection, and classification of specific machine sounds: the individual cylinder firings of a marine engine. For this task, a four-step procedure has been ...
ArXiv, 2016
This work presents a new toolkit for describing the acoustic properties of the ocean environment before, during and after a sound event caused by an underwater seismic air-gun. The toolkit uses existing sound measures, but uniquely applies these to capture the early time period (actual pulse) and late time period (reverberation and multiple arrivals). In total, 183 features are produced for each air-gun sound. This toolkit was utilized on data retrieved from a field deployment encompassing five marine autonomous recording units during a 46-day seismic air-gun survey in Baffin Bay, Greenland. Using this toolkit, a total of 147 million data points were identified from the Greenland deployment recordings. The feasibility of extracting a large number of features was then evaluated using two separate methods: a serial computer and a high performance system. Results indicate that data extraction performance took an estimated 216 hours for the serial system, and 18 hours for the high perfo...
The Journal of the Acoustical Society of America, 2021
Detecting acoustic transients by signal-to-noise ratio (SNR) becomes problematic in nonstationary ambient noise environments characteristic of coral reefs. An alternate approach presented here uses signal directionality to automatically detect and localize transient impulsive sounds collected on underwater vector sensors spaced tens of meters apart. The procedure, which does not require precise time synchronization, first constructs time-frequency representations of both the squared acoustic pressure (spectrogram) and dominant directionality of the active intensity (azigram) on each sensor. Within each azigram, sets of time-frequency cells associated with transient energy arriving from a consistent azimuthal sector are identified. Binary image processing techniques then link sets that share similar duration and bandwidth between different sensors, after which the algorithm triangulates the source location. Unlike most passive acoustic detectors, the threshold criterion for this algorithm is bandwidth instead of pressure magnitude. Data collected from shallow coral reef environments demonstrate the algorithm's ability to detect SCUBA bubble plumes and consistent spatial distributions of somniferous fish activity. Analytical estimates and direct evaluations both yield false transient localization rates from 3% to 6% in a coral reef environment. The SNR distribution of localized pulses off Hawaii has a median of 7.7 dB and interquartile range of 7.1 dB.