Acoustic signature

The term acoustic signature is used to describe a combination of acoustic emissions of sound emitters, such as those of ships and submarines. In addition, aircraft, machinery, and living animals can be described as having their own characteristic acoustic signatures or sound attributes, which can be used to study their condition, behavior, and physical location. Acoustic homing and Acoustic torpedo The analysis of acoustic signatures is an important adjunct to passive sonar used to track naval warships and weapons. Similar methods have been used to identify aircraft, especially before the development of sophisticated radar tracking. The acoustic signature is made up of a number of individual elements. These include: Machinery noise: noise generated by a ship's engines, propeller shafts, fuel pumps, air conditioning systems, etc. Cavitation noise: noise generated by the creation of gas bubbles by the turning of a ship's propellers. Hydrodynamic noise: noise generated by the movement of water displaced by the hull of a moving vessel. These emissions depend on a hull's dimensions, the installed machinery and ship's displacement. Therefore, different ship classes will have different combinations of acoustic signals that together form a unique signature. Hydrophones and sonar operating in passive mode can detect acoustic signals radiated by otherwise invisible submarines, and use these signals to target attacks. Modern naval mines and torpedoes such as the CAPTOR mine can be programmed to distinguish the acoustic signatures of different vessels, leaving friendly vessels unmolested and attacking high-value targets when faced with multiple possible targets, e.g. distinguishing an aircraft carrier from its escorts. Acoustic quieting Warship designers aim to reduce the acoustic signature of ships and submarines just as much as they aim to reduce the radar cross sections and infra-red signals. For submarines, as a prime factor in how they can be detected the reduction of the acoustic signature is a primary goal.