Ambient noise in the natural surf zone: wave breaking frequencies

Ambient noise in the surf zone, in the frequency range 120 Hz to 5 kHz, was recorded using a broadband hydrophone, located approximately one meter above bottom and 1-2 metres below the mean sea surface. The predominant source of this noise is breaking waves. Analysis of simultaneous land-based video observations of the sea surface in the region of the hydrophone, along with wave height data, reveals quantitative correlation between wave-breaking events and the hydrophone signal. In energetic surf, locally breaking waves appear as discrete events in the ambient noise spectra. The detection by the hydrophone of breaking waves in the immediate vicinity implies that ambient noise in heavy surf provides a means of studying breaking wave statistics in the surf zone in situ; in particular, the frequency of occurrence of local breaking.