Estimating the source level for wind-driven underwater noise from long-term archival data

Sound from wind and waves sets the background sound levels throughout the ocean. An accurate source level for wind is needed to estimate the ambient sound levels for sound exposure modeling, environmental assessments, or detection performance of sonars. Previous models had a constant roll-off of the sound levels at −16 dB/decade at all wind speeds, and the source levels at frequencies below ∼1 kHz were flat due to a lack of measurements. Here, we analyzed 14 long-term archival datasets with limited anthropogenic sound sources to estimate the wind-driven source level. We estimated the site-specific propagation loss using a ray-based model, then added the loss to the median received levels at each wind speed to obtain the source level. The results showed that there is a peak in the source level at ∼500 Hz. At high frequencies, the roll-off increases with wind speed, from ∼12 dB/decade at 3 m/s to >25 dB/decade at 20 m/s. An analytic equation for the aeric dipole source level will be provided that increases as wind speed cubed, like most other air–ocean coupling processes. A comparison of the new model to previous direct source level measurements and the Wenz curves will be provided.