No abstract

The sonic anemometer is widely recognized as a precise and accurate instrument for measuring and studying atmospheric wind speed and turbulence that works on the principle of measuring the difference in the transit time of acoustic pulses along a known path length. Desirable characteristics of the sonic anemometer include lack of moving parts, linear dynamic response, and good directional response. However, the sensor probes and support structures inevitably lead to a deformation of the flow field being examined resulting in transducer shadowing and flow distortion errors. An empirical method of determining the effects of flow distortion errors on measurements is utilized. While deviations in the horizontal wind are negligible, investigations clearly indicate the need for correction of raw data on vertical wind measurements. Simulations have been conducted using a synthetic time series to determine the impact of observed errors on turbulence, with indications that measurements have a dependence on the angle of attack. Using the series at angles of elevation varying between -12° and 12°, a deviation in turbulence by over 30% is observed for certain wind directions. Matrices derived from the errors at different angles of attack have been used to correct standard ten-minute time series of field data resulting in a decrease in the measured turbulence strength by between 7 and 10%.