A review of wind sound source level derived from ambient noise data

Experimental estimates of source levels of sound generated by local wind at the sea surface are derived from ambient noise data based upon assumptions about the nature of the wind sound source. Generally, the sound source is assumed to be a distribution of monopole sources near the sea surface or a distribution of dipoles at the sea surface. Depending on the assumption made, the source level estimates for low frequencies (<∼400 Hz) can be significantly different by several decibels. These differences have led to confusion about the nature of the sound source in modeling wind noise. This paper presents a critical review of experimental techniques and analysis procedures for deriving wind sound source levels from low-frequency ambient noise data. The study finds that the differences in published estimates from experiments with vertical line hydrophone arrays can be understood through a simple analysis of the source assumptions. The work shows that the source levels agree well for wind speeds greater than 5 m/s. However, knowledge gaps exist about source levels at very low frequencies below 100 Hz and wind speeds less than 5 m/s. New experiments with vertical line arrays are needed to resolve these questions.