Sonic anemometer (co)sine response and flux measurement; II the effect of introducing an angle of attack dependent calibration

The response of R2 and R3-type solent ultrasonic anemometers was tested in a series of wind tunnel experiments. The vertical wind velocity was found to be seriously undermeasured for large angles of attack. The error in the horizontal windspeed components was also found to be considerable at large angles, but the magnitude of the error depends on wind direction. An angle of attack dependent calibration is derived to correct for these response errors. Application of this angle of attack dependent calibration to data collected over two sites, one a relatively smooth peat bog area and the other a pine forest, shows that the uncorrected covariances representing the fluxes of momentum, sensible and latent heat, and carbon dioxide increase initially by 5–15%. However, interactions between the angle of attack dependent calibration and the second axis rotation correction (setting ) resulted in the final change in momentum flux being -9% on the peat bog area (-4% on the pine forest), but +5% (+15%) for sensible heat flux, +5% (+7%) for latent heat flux and -2% (+9%) for the carbon dioxide flux. The amount of change was related to the vegetation roughness and the flux-angle distributions.