Underwater radiated noise from modern commercial ships

TLDR

Calibrated acoustic data (<1000 Hz) from an autonomous seafloor‑mounted recorder were combined with AIS ship‑passage information to measure source level, sound exposure level, and transmission range for seven modern commercial ship types. Measurements revealed that different ship types exhibit distinct acoustic levels and spectra, with a 54 kGT container ship producing the highest broadband source level (188 dB re 1 µPa@1 m) and a 26 kGT chemical tanker the lowest (177 dB), bulk carriers peaking near 100 Hz, container ships and tankers below 40 Hz, asymmetric radiation with stern levels 5–10 dB higher than bow, and simple predictive models based on ship characteristics proved inadequate.

Abstract

Underwater radiated noise measurements for seven types of modern commercial ships during normal operating conditions are presented. Calibrated acoustic data (&amp;lt;1000 Hz) from an autonomous seafloor-mounted acoustic recorder were combined with ship passage information from the Automatic Identification System. This approach allowed for detailed measurements (i.e., source level, sound exposure level, and transmission range) on ships of opportunity. A key result was different acoustic levels and spectral shapes observed from different ship-types. A 54 kGT container ship had the highest broadband source level at 188 dB re 1μPa@1m; a 26 kGT chemical tanker had the lowest at 177 dB re 1μPa@1m. Bulk carriers had higher source levels near 100 Hz, while container ship and tanker noise was predominantly below 40 Hz. Simple models to predict source levels of modern merchant ships as a group from particular ship characteristics (e.g., length, gross tonnage, and speed) were not possible given individual ship-type differences. Furthermore, ship noise was observed to radiate asymmetrically. Stern aspect noise levels are 5 to 10 dB higher than bow aspect noise levels. Collectively, these results emphasize the importance of including modern ship-types in quantifying shipping noise for predictive models of global, regional, and local marine environments.