NEON sonic anemometer blocking error experiment, NEON Headquarters, 2014

The eddy-covariance technique is widely applied to observe the exchange of energy and scalars between the earth’s surface and its atmosphere. In practice, fast (≥10 Hz) sonic anemometry and enclosed infrared gas spectroscopy are used to determine fluctuations in the 3-D wind vector and trace gas concentrations, respectively. Here, two contradicting requirements need to be fulfilled: (i) the sonic anemometer and trace gas analyzer should sample the same air volume, while (ii) the presence of the gas analyzer should not affect the wind field measured by the 3-D sonic anemometer. To determine the optimal positioning of these instruments with respect to each other, a trade-off study was performed. Theoretical formulations were used to determine a range of positions between the sonic anemometer and the gas analyzer that minimize the sum of (i) decorrelation error and (ii) wind blocking error. Subsequently, the blocking error induced by the presence of the gas sampling system was experimentally tested for a range of wind directions to verify the model-predicted placement: In a controlled environment the sonic anemometer was placed in the directed flow from a fan outfitted with a large shroud, with and without the presence of the enclosed gas analyzer and its sampling system. Sonic anemometer data from the experiment trials are compressed into a .zip archive. The data can be extracted with software such as 7-zip. The data are separated into 2 trials with “IRGA” and “noIRGA” subfolders. In each subfolder, there are comma-separated values (csv) files that correspond to the incident wind angle (0-350 degrees) and the Cartesian axis of the wind component (x, y, and z), i.e. “10_x.csv”.