Underwater Acoustic Environment of Coastal Sea With Heavy Shipping Traffic: NE Baltic Sea During Wintertime

Abstract

<p>Shipping is the most pervasive source of anthropogenic underwater continuous noise<br />and local intermittent noise. This study focused on the separation of anthropogenic<br />intermittent noise from dynamic background noise in the Gulf of Finland using an<br />adaptive threshold level (ATL) technique. The intermittent noise was validated with<br />Automatic Identification System (AIS) data and the background noise with selected<br />environmental factors. Separated components were characterized and compared with<br />a sound exposure level (SEL) in three 1/3 octave bands. Intermittent noise can be<br />separated with ATL in the Baltic Sea, and vessel traffic identified as the primary source.<br />Background noise varies spatially and is partially explained by environmental factors.<br />Intermittent noise has strong persisting influence on the acoustic environment near<br />shipping lanes, elevating the SEL in each of the 1/3 octave bands: by 20–30 dB in<br />the 63 Hz band, by 13–22 dB in the 125 Hz band and by 5–8 dB in the 2000 Hz<br />band. We conclude that strong intermittent noise is characteristic to the underwater<br />acoustic environment in the study area with heavy shipping traffic. By combining ATL<br />with data from AIS, intermittent noise peaks in underwater hydrophone recordings can<br />be associated with passages of individual vessels.<br />Keywords: underwater noise, shipping, AIS, adaptive threshold level, Baltic Sea, intermittent noise, noise<br />threshold<br /></p>