Csat3 Azimuth; Csat3 Right Hand Coordinate System, Horizontal Wind Vector Angle Is 0 Degrees - Campbell Open Path Eddy Covariance System Instruction Manual

Open Path Eddy Covariance System

3.2.1 CSAT3 Azimuth

NOTE
14
The example programs report the wind direction in both the CSAT3 coordinate
system (a right-handed coordinate system) and in the compass coordinate
system (a screwball left-handed coordinate system). The CSAT3 coordinate
system is relative to the CSAT3 itself and does not depend on the CSAT3's
orientation (azimuth of the negative x-axis). The compass coordinate system is
fixed to the earth. In order for the programs to compute the correct compass
wind direction, the azimuth of the CSAT3 negative x-axis must be entered into
the program. The program default value for CSAT3_AZIMUTH is 0. This
assumes that the prevailing wind is from the North, e.g. the CSAT3 is mounted
such that the negative x-axis points to the North.
As described in Section 2 and 2.2.1, orient the CSAT3 so that it is pointing into
the prevailing wind direction. If you have done so, the CSAT3 negative
x-axis will point into the prevailing wind direction. Enter this prevailing wind
direction for the constant CSAT3_AZIMUTH (see the station log book for this
bearing).
Don't forget to account for the magnetic declination at the site;
see Appendix A for details.
Figures 11 and 12 show the orientation of a CSAT3 with a compass bearing of
140 degrees, e.g. the negative x-axis is pointing into 140 degrees. If the wind
is blowing into the CSAT3, from the negative x-axis to the positive x-axis
(from the transducers to the block), the horizontal wind vector angle
(wind_dir_csat3) is 0 degrees (wind vector) and the compass wind direction
(wnd_dir_compass) is 140 degrees (wind vane).
Wind Vane
Wind Vector
FIGURE 11. CSAT3 Right Hand Coordinate System,
Horizontal Wind Vector Angle is 0 Degrees
Y
North
X