Modelling of underwater radiated noise from ships measured at the Lofoten-Vesterålen cabled observatory

Time histories of broadband ship noise measured at the Lofoten-Vesterålen cabled observatory (on the seafloor at 255 m depth in the Norwegian Sea) are compared to model-based predictions. Fifty-four tracks of 26 different vessels are included in our analysis; all 54 ship tracks pass within 520 m horizontally of the hydrophone. Ships were tracked using the Automated Identification System. A striking feature of the ship noise measurements is azimuthal anisotropy of the sound radiated by the passing ships; sound intensity aft of the vessels is higher than sound intensity fore of the vessels. Anisotropy of the radiated ship noise is accounted for in the ship noise propagation model used. Agreement between measurements and model predictions is good. Estimates of ship-radiated acoustic power and an azimuthal anisotropy strength parameter are obtained for each ship track. Estimates of the azimuthal anisotropy strength parameter depend on vessel type. Estimates of the azimuthal anisotropy strength parameter among different tracks of the same vessel show considerable variability, and estimates of radiated acoustic power show no clear increase with increasing ship speed; these unexpected results suggest that factors not accounted for in our analysis, including ship displacement, play a role in controlling the radiated ship noise.