Real-Time Monitoring of Underwater Radiated Noise Levels from Ships

Commercial ships are the most common anthropogenic sound sources in the ocean today. Only a few monitoring stations exist where opportunistic measurements and estimations of ships’ underwater radiated noise (URN) can be performed. This chapter describes the development and operation of a cabled real-time hydrophone station, located outside a major port on the west coast of Sweden. The station was designed to record the local ambient noise and obtain opportunistic measurements of large numbers of commercial ships passages in relatively shallow, 46 m, waters. The propagation loss was measured twice to reduce the uncertainty in the SL estimations. During the measurement period, the source level (SL) for 254 opportunistic commercial ship passages was estimated. One particular cargo ship passed the station 23 times, resulting in multiple URN estimations and the possibility to investigate the effect of different propagation loss conditions on the calculated SL. Finally, the calculated SL was compared to SL models commonly used in the production of soundscape maps.