Anti-intruder port protection “MAC (Magnetic ACoustic) System”: advances in the magnetic component performance

Abstract

In the following, we report the advances made in the development of a magnetic component for peripheral monitoring of port environments for anti-intruder systems. The project was initiated by the Office of Research and Development, COMFORDRAG, Italian Navy, in 2004, with the aim of improving the detection performance of current acoustic-based anti-intruder systems, in the vicinity of quays or the seabed or in acoustic-shadow zones behind natural or artificial objects. In the five-year period from 2004 to 2008, the system has been subjected to detection-performance tests in experiments involving divers equipped with air tanks and rebreather kits in real port environments and, at the same time, the associated signal processing has been subjected to development, to enhance detection performance. In tests involving simulated diver attacks against a vessel moored alongside a quay in the port of La Spezia, the system has been proved particularly effective by detecting 9 divers out of 9. The processing of the magnetic signal has been enhanced by implementing an amplitude threshold, as a means of filtering the passive energy components, termed Passive Energy Cutting (PEC), that is, the elimination of components that comprise no useful information regarding diver transits. The use of PEC boosts the reliability of the system in terms of detection versus false alarm rate, as evidenced by the comparison of the ROC curves for the system with and without PEC.