A cost effective system for light acoustic signature assessment of surface vessels

摘要

This paper describes a cost effective system developed to estimate underwater acoustic emissions of surface vessels. The system, which doesn't replace tests in range facilities, it's rather intended to provide a light approach to underwater acoustic measurements, and can be easily deployed at sea from the 'target' ship itself or from a little supporting boat. It is particularly useful, for example, in checking the vessel signature during preliminary sea trials, after refitting operations or just before a mission. The battery powered system is composed of a spar buoy and a receiving station. The battery powered buoy is provided with an omni-directional hydrophone, a GPS receiver, a wireless transmitter and an embedded PC. The on board receiving station is composed of a notebook, a GPS receiver, a wireless receiver, an acquisition board and of an ad hoc developed software for acquisition and acoustic post-processing. The receiving station include a tracking system able to help the ship to follow the correct approach in test run. Data are stored on the solid state memory of the buoy and at the same time transferred through the wireless link to the receiving station on board, to be processed in real time. The two GPS receivers allow to compensate the measured levels with the actual distance. Moreover signals from accelerometers placed on board near relevant machineries and on the radiating hull can be acquired by the on board receiving station to better correlate radiated noise and ship sources. Depending on the background, the intrinsic very low noise level, allows the acquisition of the acoustic signature not only of the commercial, but also of the more silent military ships. Experience and feed-back from the use of the system at sea on different vessels are included in the paper.