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FIGURE 6-7. Compass coordinate system, compass wind direction is 140 degrees
6.6 Leveling
Leveling the CSAT3BH within a couple degrees is usually sufficient. The user commonly applies
coordinate rotations to time series data to report the three-dimensional wind in a coordinate
system where the x- and y-axes lie along the streamwise wind plane.
Adjust the anemometer head so that the bubble within the level on top of the CSAT3BH block is
in the bullseye. Firmly grasp the sonic anemometer block, loosen the bolt underneath the block,
and adjust the head accordingly. Finally, tighten the bolt with a 9/16-in wrench.
If an application requires greater accuracy in inclination of the CSAT3BH, or if an application
requires a measurement that shows if, and when, the inclination of the CSAT3BH changes over
time (for example, a sagging crossarm or tower tilt), an integrated inclinometer in the CSAT3BH
can give pitch and roll measurements.
Pitch is the angle between the gravitationally horizontal plane and the CSAT3BH x-axis. A positive
pitch angle corresponds to a clockwise rotation about the y-axis when looking down on the
y-axis (see
(p. 37)). In other words, a positive pitch angle occurs when the transducer
end of the CSAT3BH is pointed downwards, while a negative pitch angle occurs when CSAT3BH
is pointed upwards.
Roll is the angle between the gravitationally horizontal plane and the CSAT3BH y-axis. A positive
roll angle corresponds to a counter-clockwise rotation about the x-axis when looking down the
x-axis (see
CSAT3BH Three-Dimensional Heated Sonic Anemometer
36