Underwater sound directionality of commercial ships

The underwater sound radiated by commercial ships is an unintended by-product of their operation and one of the most significant contributors to man-made noise at low frequencies in the ocean. To estimate the directionality of underwater sound radiated by current commercial ships, a seafloor array of five high-frequency acoustic recording packages (HARPs) deployed to 1 km depth with a maximum horizontal aperture of 1 km was used. As a ship of opportunity passed over the HARP array, the directions from the ship to each HARP along with the corresponding source levels were estimated for each ship location. Ships were tracked via satellites (Automatic Identification System—AIS) and acoustically by a frequency domain beamformer that was implemented for one of the HARPs configured with a volumetric hydrophone array (2 m maximum aperture). The directionality estimates of contemporary commercial ships exhibit significant stern-bow asymmetries among other quantitative characteristics that will be discussed.

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