An instrument for the in situ measurement of sea surface noise from a depth of 1 m under low wind conditions

Abstract

An underwater package has been developed and deployed to determine the cause of surface noise generated at low wind speeds. The self-suspending instrument, tethered 1 km from a support ship, contains a video camera and four hydrophones, as well as orientation sensors. The signal from each hydrophone is filtered and digitized to cover a frequency range of 800–8000 Hz. Data recorded from a depth of 1–2 m indicates that considerable noise is generated by tiny surface spills. The sound from each spill is composed of distinct decaying oscillations which only last for a few milliseconds. These oscillations match the resonant bubble signatures described by Strasberg [J. Acoust. Soc. Am. 28, 20–26 (1956)] and Medwin and Beaky [J. Acoust. Soc. Am. 86, 1124–1130 (1989)].