The effect of ocean fronts on acoustic wave propagation in the Celtic Sea.

Underwater noise is now classed as pollution in accordance with the Marine Strategy Framework Directive. Noise from shipping is a major contributor to the ambient noise levels in ocean, particularly at low (< 300 Hz) frequencies. This paper studies patterns and seasonal variations of underwater noise in the Celtic Sea by using a coupled ocean model (POLCOMS) and an acoustic model (HARCAM) in the year 2010. Two sources of sound are considered: (i) representing a typical large cargo ship and (ii) noise from pile-driving activity. In summer, when the source of sound is on the onshore side of the front, the sound energy is mostly concentrated in the near-bottom layer. In winter, the sound from the same source is distributed more evenly in the vertical. The difference between the sound level in summer and winter at 10 m depth is as high as 20 dB at a distance of 40 km. When the source of sound is on the seaward side of the front, the sound level is nearly uniform in the vertical. The transmission loss is also greater (~ 16 dB) in the summer than in the winter for shallow source while it is up to ~ 20 dB for deep source at 30 km. [ABSTRACT FROM AUTHOR]