Observations of underwater sound at frequencies below 1500 Hz from breaking waves at sea

An experiment was performed to obtain underwater sound recordings at frequencies below 1500 Hz from a patch of sea surface in the presence of breaking waves, concurrently with video recordings of events in the patch. The sound recordings were obtained using a vertical array in end-fire mode. Some results are presented for wind speeds of 10 and 15 m s−1. The sound recordings consist of series of discrete bursts of sound, each burst lasting a few seconds. The stronger bursts are readily identified with breaking waves. The weaker bursts are attributed to smaller breakers obscured from view. The sound is generated during the breaking phase. The spectral components are observed at all frequencies down to 75 Hz (down to 50 Hz at times of less shipping). The increase in spectrum level is 10 to 15 dB. In general, the spectrum appears to evolve with the breaking phase, the higher frequency components arising first, at the onset of breaking, the lower frequency components arising a second or more after.