Measurement of vessel underwater noise signature

Radiated underwater noise from vessels is a key parameter for target detection and classification in the sea by means of sonar. In fishery, hydroacoustic systems are used for scientific and industrial purposes, to characterize the distribution of pelagic species, estimate stock abundance, observe fish behavior, locate fish shoals, control net position and estimate catch. Adverse fish reaction to ships and disturbances in operation of sensitive hydroacoustic instrumentation as a consequence of excessive ship noise is a well known fact and has been investigated internationally. Noise reduction measures have to be introduced in all stages of ship design and include preventing vibration transmission from rotating machines to the ship hull and reducing propeller generated noise. Successfulness of such measures can be verified only by ship sea trials at specialized noise measurement ranges. Low-noise hydrophones and modern digital instrumentation enable in-situ measurement of vessel hydroacoustic signatures in the whole frequency range of interest and investigation of noise sources.