Oceanic low frequency ambient noise

Ambient noise has been attributed to bubbles spray and splash produced by wind action and breaking waves at the higher frequencies. However, the large bubbles required to produce low frequency noise are not found at sufficient depths and consequently whether low-to-mid-frequency noise (LMF, 10-500 Hz) was produced and by what mechanism has been a subject of recent research. LMF ambient noise measurements were often dominated by emissions from ships and industrial activity making observations of local noise mechanism difficult. Wave-wave interaction, wave-turbulence interaction and the pressure fluctuations due to the turbulent boundary (TBL) layer above the sea surface were all examined as a LMF mechanism but were found radiate insufficient sound. Breaking waves were found to produce microbubble plumes and clouds while at the same time radiating low frequency sound. Consequently collective oscillations of these compact microbubble clouds, were proposed as a mechanism and experimentally verified as a source of LMF noise. This paper discusses LMF noise characteristics, mechanisms and calculations of basin noise based on the breaking wave as a random source of sound.