Underwater noise footprint measurements on a survey vessel

The potential impact of man-made underwater noise on the marine environment is receiving increased attention. Shipping is one of the main sources of such anthropogenic noise. In order to understand the underwater soundscape considerable effort is being placed on generating underwater noise maps, based on using AIS data to provide details of vessel locations and operational characteristics. A key input for noise mapping models is an adequate knowledge of the source strength and characteristics for each vessel. Currently the sources are usually assumed omnidirectional, given the limited data on the true vessel radiation pattern. As part of the EU SONIC (Suppression of underwater Noise Induced by Cavitation) project measurements were undertaken on a small survey vessel, operating under realistic conditions at sea in shallow water. An autonomous recorder was used to measure the sound pressure as a function of range and azimuth. The vessel made a repeated runs past the autonomous recorder for a variety of different ranges. This has enabled the vessel noise footprint to be measured as a function of frequency and speed for the vessel, showing how the azimuthal characteristics change with frequency.