Measurement of the underwater noise footprint of a vessel

The Impacts of man-made underwater noise on the marine environment have received increased attention over recent years, primarily resulting from recognition of the increased pressures placed on the oceans by human activities. A main source of such anthropogenic noise is shipping. 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. This paper presents the result of a trial undertaken on a small survey vessel, operating under realistic conditions at sea in shallow water, as part of the SONIC project. This trial used an autonomous recorder 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.