Container ship source level and directionality measurements

Abstract

Underwater radiated noise from container ships was measured opportunistically from multiple spatial aspects to estimate directionality and signature source levels. Transiting ships were tracked via the Automatic Identification System in a shipping lane while acoustic pressure was measured at the ships’ keel and beam aspects. Port and starboard beam aspects were 15, 30, and 45 deg in compliance with ship noise measurements standards [ANSI/ASA S12.64 (2009) and ISO 17208-1 (2016)]. Source levels were derived with a spherical propagation (surface-affected) or a modified Lloyd’s mirror model to account for interference from surface reflections (surface-corrected). Ship source depths were estimated from spectral differences between measurements at different beam aspects. In addition, recordings were made at a ∼10 deg starboard aspect and utilized to measure and compare signatures of MAERSK G-class container ships before and after the ships were equipped with new propellers as part of MAERSK’s $100+ million Radical Retrofit Program.