Passive acoustics embedded on gliders—Weather observation through ambient noise

Underwater gliders can provide high resolution water temperature and salinity profiles. Being able to associate them with a surface weather conditions estimation would allow to better study sea-air interactions. Since in-situ observations of the marine meteorological parameters are difficult, the development of a glider embedded weather sensor has been studied, based on the WOTAN approach. In the 1–30 kHz frequency range, the background underwater noise is dominated by wind generated noise. Focusing on the sound pressure level at 5, 8, 10, and 20 kHz allows to estimate the wind speed. Thus, deploying a glider with an embedded hydrophone gives an access to the surface weather conditions around its position. We have deployed gliders in the Mediterranean sea, with passive acoustic monitoring devices onboard. Four months of data have been recorded. Wind speed estimations have been confronted to weather buoys observations and atmospheric models predictions. Wind estimates have been obtained with a ~2 m/s error. A specific emphasis has been placed on the robustness of the processing through multi frequencies analysis and depth induced attenuation correction. A downscaling study has been performed on the acoustic sampling protocol, in order to meet the low energy consumption glider standards, for a future real time embedded processing. The glider generated noise and its vertical movement are not perturbing the estimation. Moreover, the surface behavior of the Slocum gliders allows an estimation of the wind direction.