Understanding Radiated Underwater Noise Levels Measured at Different Sound Ranges

Awareness of underwater noise ˜pollution' is an issue leading towards international regulations for merchant shipping. Therefore, measuring radiated noise in beam aspect is gaining relevance. An important topic is the reported ship acoustic signature at different ranges with various hydrophone configurations and how the environment affects those measurements. During the international trial RIMPASSE 2011, the research vessels CFAV QUEST and RV PLANET were measured at shallow and deep water sound ranges throughout Europe, using predefined conditions and procedures. Structure borne sound was monitored using numerous on-board mounted accelerometers. Both vessels were measured at the static sound ranges of Loch Goil (UK) and Aschau (GE). Sailing runs were carried out at the dynamic sound ranges of Loch Fyne (UK), Heggernes (NO) and Aschau. Results of those trials have been reported previously. However, the main focus of those papers lay in the range comparison, utilizing hydrophone configurations in keel aspect, at a certain water depth in the acoustical near field of the sources. Additionally, focus lay on controllable and reproducible sources such as onboard shakers and towed hydroacoustic sources. The current paper, however, is focusing on different hydrophone configurations at the various sound ranges in beam aspect.