Determining Air-Sea Interaction Exchange Coefficients in Low Winds Using Small UAS

In the boundary layer, the exchange of momentum, heat, and moisture occurs between the atmosphere and ocean. Since it is too dangerous for a crewed aircraft to fly within 10 meters of the ocean surface to directly obtain these measurements, a sUAS (Small Uncrewed Aircraft System) is one of the only viable options. In March of 2023 a BlackSwift Technologies S0 sUAS was deployed from the NOAA P-3 on a calm clear day with ~5 m/s winds in the Gulf of Mexico off the coast of Sarasota, Florida. At the end of the mission, the sUAS flew a total of 8 legs (flight paths) in a straight line roughly 10 meters above the ocean surface for over 12 minutes. For each leg, the 4-Hz data was used to calculate, for the first time using a sUAS, momentum flux, heat flux, and moisture flux using both direct methods and the bulk aerodynamic formulas. Furthermore, we use these methods to calculate the exchange coefficient of momentum flux (C­_D), the exchange coefficient of enthalpy flux (C_K), and the exchange coefficient of sensible heat (C_H). This study demonstrates the framework and ability for using sUAS to measure air-sea interactions. Future intention is to use sUAS to obtain similar measurements in hurricanes which could better help understand hurricane intensification and improve model physics.