Science Meetings

Measuring Oceanic Wind Speed and Rainfall Rate Using Underwater Ambient Sound
Nystuen, J.A., Yang, J., and Asher, W.E. (26-Feb-14)

Wave breaking from wind and the impact of raindrops produce distinctive underwater sounds that can be used to detect and then quantify rainfall rate and wind speed. The sound production physics are co-mingled, requiring that quantitative algorithms for wind speed and rainfall rate be functions of one another. For wind-driven seas wave breaking is closely correlated with wind speed, allowing acoustic wind speed measurements of accuracy ±0.5 m/s. The acoustic signature of rain is easily detected at low to moderate wind speeds. Here, we present a sampling strategy and an objective acoustic classification of the underwater sound generated by wind and rain that can be used to retrieve wind speed and rain rate. The method was tested using data collected at Ocean Station PAPA (50N, 145W). Acoustically derived wind speeds are compared to wind speeds made from buoy-mounted anemometers. The acoustic rainfall rate measurement is constrained by rainfall accumulation data from a surface-mounted rain gauge on the mooring. This technology can be implemented on a variety of innovative new ocean instrumentation platforms including drifters, gliders and sub-surface moorings. [Funding from ONR, NSF and NASA under the Aquarius Mission and Sea Surface Salinity science team.]