The character of underwater noise radiated by small vessels

This paper presents an overview of our initiatives for underwater noise measurements and their acoustic characteristics, which years ago have been applied. Different kinds of surface ships and more importantly submarines radiate high levels of underwater noise which can be detected and tracked by passive sonars. Hostile navies use these signatures for detection and classification of targets. In many cases, not only a vessel as a specific class of warship, but also even the individual ship within a concrete class can be positively identified. The method of narrow-band filtration of the spectrum' s discrete lines at frequencies up to several H: is the basic standard of passive systems for long-distance detection. To find the source of noise, the level of vibration was also measured by accelerometers. Ship' s very own distinctive acoustic signature radiated at discrete frequencies, excited by the machinery, is easily detected and must be decreased as much as possible. Coherence between underwater sound pressure from a moving vessel and vibration during the same run was made.