Fused passive acoustic and electric detection of divers

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.