Crosswind correction

In a 3-dimensional sonic anemometer, the sonic temperature (T_si) is estimated on each of the three measurement paths. The three estimates are then averaged into a single value of sonic temperature (T_s). The crosswind correction accounts for the effect of a wind component normal to the measurement path on each estimation of the sonic temperature:

6‑6

where is the corrected sonic temperature and V_ni is the wind component normal to the i^th axis. Components V_ni can be derived from actual (instantaneous) wind measurements in the anemometer’s coordinate system with a simple geometrical transformation:

6‑7

Where u_m and v_m are the measured wind components in the horizontal axes of the anemometer, and A_i, B_i, and C_i are geometrical factors for the i^th axis that depend on the geometry of the anemometer. Table 1 in Lui et al. (2001) gives geometrical factors for the following anemometers:

• CSAT3, Campbell^® Scientific, Inc.
• R2, R3, R3A, HS by Gill Instruments
• USA-1 by Metek

Note: The correction is already applied in the firmware of some anemometers (e.g., the CSAT3). In these cases, applying the correction in EddyPro will result in double accounting.

We recommend that you verify the settings in the instructions for your anemometer. Use the correction in EddyPro according to the following scenarios.

• The correction is not implemented in the firmware. In this case we suggest checking this option and let EddyPro perform the correction;
• The correction is implemented in the firmware and it is not possible to turn it off. In this case you should clear this option in EddyPro to avoid double accounting;
• The correction is available in the firmware as an option. In this case, you can decide to apply either the native correction or the EddyPro correction.