Measurements of Flow Distortion within the CSAT3 Sonic Anemometer

Abstract:

We have measured flow distortion within the CSAT3 sonic anemometer using two quite different techniques. One method compares three adjacent, differently-aligned CSAT3 sonics to each other, using a data analysis technique similar to that of Kochendorfer et al.~(2012). The two 'outside' sonics are upright references while the central, test sonic is oriented with its v-axis vertical, so that fluctuations of wind direction are surrogates for variations in the vertical wind component. The second technique compares CSAT3 measurements to independent velocity measurements with a 3-component Doppler LIDAR. The LIDAR is focused at a distance of 0.8 m in front of the sonic and is thus a flow-distortion-free reference. Here we compare the results of the two techniques to each other, as well as to a transducer-shadowing model for CSAT3 flow distortion. On the basis of these measurements, recommendations are made for correction of CSAT3 flow distortion.