On Estimating Wind Velocity Using an Upward-Looking ADCP

Abstract

A new set of measurements made using an upward-looking broadband acoustic Doppler current profiler (ADCP) is analyzed for ?surface velocity,? which previous investigations suggest is related to wind velocity. In the present case, use of a shallow instrument depth and 1-m-depth resolution are shown to yield both a surface return, identified by a maximum in backscatter intensity (similar to previous studies), and a subsequent return that corresponds to a maximum in speed. These returns have speeds (measured relative to the 2-m-depth current) that increase to a peak of 0.7?0.8 m s?1 at a wind speed of 4?5 m s?1 and decrease for higher wind speeds, a behavior similar to that found by Nakajima et al., who made ADCP measurements using the same incidence angle (20°) as in the present study. A new finding is that the return having maximum speed yields a direction that better approximates the wind direction (a mean difference of about 5°) over the range of wind speeds sampled (up to 17 m s?1). Suggestions are made for future investigations.