Campbell Scientific CSAT3B CSAT3B Three-Dimensional Sonic Anemometer - Page 37

CSAT3B Three-Dimensional Sonic Anemometer FIGURE 7-4. CSAT3B mounting 7.4 Leveling Leveling the CSAT3B within a couple degrees is usually sufficient. The user commonly applies coordinate rotations to time-series data to report the threedimensional wind in a coordinate system where the x- and y-axis lie along the stream wise wind plane. Over level terrain, adjust the anemometer head so that the bubble within the level on top of the CSAT3B block is in the bullseye. Over sloping terrain, adjust the anemometer head so that the horizontal surface upon which the bubble level is mounted is parallel to the terrain. 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 CSAT3B, or if an application requires a measurement that shows if, and when, the inclination of the CSAT3B changes over time (for example, a sagging crossarm or tower tilt), an integrated inclinometer in the CSAT3B can give pitch and roll measurements. Pitch is the rotation about the CSAT3B y-axis and is given by the smallest angle between the CSAT3B x-axis (see FIGURE 7-5) and a horizontal plane. A positive pitch angle corresponds to a clock-wise rotation about the y-axis when looking down on the y-axis. In other words, a positive pitch angle occurs when the transducer end of the CSAT3B is pointed downwards, while a negative pitch angle occurs when CSAT3B is pointed upwards. Roll is the rotation about the CSAT3B x-axis, and is given by the angle between the CSAT3B z-axis and an imaginary axis that is normal to the gravitationally level plane. A positive roll angle corresponds to a counterclockwise rotation about the x-axis when looking down the x-axis. 27