In this paper we investigate if underwater electrode arrays can complement hydrophones in passive surveillance situations with occasionally poor hydroacoustic conditions. The application is ...classification of passing surface ships as either light or heavy. Different signal processing and fusion techniques are compared in conjunction with a support vector machine classifier. It is shown that in some situations, the fusion of electrode and hydroacoustic data actually improves the performance of the passive surveillance system. At best, our system correctly classifies 22 ship passages out of 23 possible
Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore ...have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions. The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova, as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water or ice. Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations.
Both absorption and scattering of light at wavelengths 410 to 610 nanometers were measured in the South Pole ice at depths 0.8 to 1 kilometer with the laser calibration system of the Antarctic Muon ...And Neutrino Detector Array (AMANDA). At the shortest wavelengths the absorption lengths exceeded 200 meters—an order of magnitude longer than has been reported for laboratory ice. The absorption shows a strong wavelength dependence while the scattering length is found to be independent of the wavelength, consistent with the hypothesis of a residual density of air bubbles in the ice. The observed linear decrease of the inverse scattering length with depth is compatible with an earlier measurement by the AMANDA collaboration (at ∼515 nanometers).
AMANDA is a high-energy neutrino telescope presently under construction at the geographical South Pole. In the Antarctic summer 1995/96, an array of 80 optical modules (OMs) arranged on 4 strings ...(AMANDA-B4) was deployed at depths between 1.5 and 2 km. In this paper we describe the design and performance of the AMANDA-B4 prototype, based on data collected between February and November 1996. Monte Carlo simulations of the detector response to down-going atmospheric muon tracks show that the global behavior of the detector is understood. We describe the data analysis method and present first results on atmospheric muon reconstruction and separation of neutrino candidates. The AMANDA array was upgraded with 216 OMs on 6 new strings in 1996/97 (AMANDA-B10), and 122 additional OMs on 3 strings in 1997/98.
In this paper we focus on passive acoustic detection and classification of divers with open circuit breathing systems. We use a method that aims to find the fundamental breathing frequency of a ...diver. For the analysis we have used data from two different sea trials. One sea trial was conducted in a remote area away from most anthropogenic activities and one sea trial was conducted in the busy port of Gothenburg, Sweden. The first data set is used to characterize the signature of the divers with open breathing systems and tune the detection algorithm. We estimate the detection performance as function of varying signal-to-noise ratio levels. The detector is finally applied to data from the second sea trial that was conducted in the port of Gothenburg.
Underwater surveillance against small and low signature targets is challenging, especially in disturbed and shallow water areas such as harbors. Today the most frequently used system for surveillance ...in harbors is active sonar. However, the detection range of an active system can rapidly degrade due to changes in the sound propagation conditions and in the ambient noise. We focus our research on how passive underwater sensors can be used as a complement to active acoustic systems. We have previously reported on diver detectors for passive acoustic and electric field data, with promising results. The use of the two sensor systems together is mainly motivated by the fact that the acoustic and electric background noise often are uncorrelated. In this paper we test different data fusion methods in order to combine the decisions from the two detectors into one unified decision. The performance of the detectors and the data fusion methods is evaluated using data from a sea trial conducted in the port of Gothenburg in 2009. We present an approach to fusion that will result in a robust system solution for harbor security.
In this paper we compare the detection performance of underwater electric-field sensors against divers using three different detection algorithms (matched filter, non-coherent and quadrature ...detectors). The detection performance is quantified and presented as ROC-curves. The empirical results are based on measurements of signatures from divers with open circuit breathing systems. They were performed during two sea-trials in diverse environments. One site is a remote area with relatively low anthropogenic activity and the other site is a busy container terminal in the port of Gothenburg, both sites in Sweden. Of the three detectors evaluated, no single detector stands out. This may imply the usefulness of fusion as a means of improving the performance in the future. In Gothenburg harbor detection of divers can be performed at signal-to-noise ratios from -20 to 0 dB, depending on the noise situation. In addition to detection, it is found that it is possible to classify a contact as a diver.
In this paper we investigate if the classification ability in littoral environments can be improved by decision fusion. We design and evaluate classifiers for discrimination of two ship types. The ...data was recorded with an underwater multisensor system at a sea trial conducted in the Baltic Sea off the east coast of Sweden. The sensor system consisted of both electrode sensors and hydrophones. The electrode sensors recorded extremely low frequency electric (ELFE) signatures and the hydrophones recorded underwater acoustic signatures of passing surface ships. Classification is performed separately on each signature and finally the separate decisions are fused into one unified decision. In addition, the possible benefits of temporal decision fusion are investigated.
In this paper we study some of the underwater background noise properties in the port of Gothenburg. The analysis includes both electric and acoustic noise. We investigate the dynamic range of the ...absolute noise power as well as its temporal variations. Furthermore, we study the spectral variations of the low-frequency noise power. Stationarity and normality tests are applied in order to quantify the amount of transients and temporal variations in the data. We find that the properties of the acoustic and electric fields are very different. The temporal variability is larger for the acoustic data. The local shipping noise is the most important acoustic source, while the wind is less important. Shipping also give rise to the highest recorded levels in the electric field noise, but due to the short detection ranges, compared with acoustics, only ships passing nearby the sensors will contribute to the background.
This paper reports a classification study using data-fusion on real-world, underwater signatures from surface ships. In this study we design and evaluate classifiers optimized to discriminate between ...small and big ships based on features extracted from extremely low frequency electric (ELFE) and hydroacoustic signatures. Classification is performed separately on each signature, and finally the individual decisions are fused into a common decision. The data set analysed here was recorded at a sea trial conducted in the Baltic Sea off the east coast of Sweden. The data set contains 23 passages of surface ships of various size, divided into small (up to 21484 tons) and big (above 21484 tons)ships based on their displacement.
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