Jeffrey A. Nystuen
Dept. of Oceanogr., Naval Postgraduate School, Monterey, CA 93943
Wave breaking and precipitation produce unique sound underwater. This sound can be used as a signal to measure wind speed and rainfall rate in oceanic regions where other in situ technologies perform poorly. A new technology using expendable autonomous acoustic drifters is described to provide these needed measurements. Nine months of data collected from three prototype acoustic drifters will be presented and compared to simultaneous estimates from a passive microwave satellite sensor (the SSM/I). Wind-speed estimates from the two technologies are well correlated, but appear to depend on water mass type. In the Pacific Ocean, the slope of the empirical relationship relating the acoustical and satellite wind-speed estimates changes significantly as the drifters move from California coastal waters to mid-Pacific tropical waters at approximately 31.5(degrees)N. This change was seasonally independent. An adjustment for local refractive conditions was applied to the acoustical data. Examples of the acoustical detection of drizzle and acoustical measurement of heavy rainfall will be presented and compared to satellite data. [Work supported by the Tactical Oceanogr. Warfare Support Prog. Office, Naval Res. Lab. Detachment, Stennis Space Center, MS.]