Publishers version - DTU Orbit

Figure 48: Cloud removal for a vertical scan CW lidar. The left plot shows the lidar conical
scan focused at a typical height above ground level. The Lorentzian sensitivity curve is also
shown; a spurious return is generated when the far wing of this curve intersects a strongly
scattering low cloud layer. The right plot shows the aerosol (red) and cloud (purple) returns
as the lidar is focused at various heights - the level of cloud contamination increases with
focus height. The cloud signal is easily identified from the 800 m focus, and these data are
then used to eliminate the cloud return at the measurement heights.
Table 5: Results of correlation analysis of 10-minute averaged horizontal wind speed for a
ZephIR 300 trial at Høvsøre, Denmark in March 2011. Gradients, m, (forced through the
origin) and coefficients of determination, R2, of unity would imply perfect agreement between
the lidar and the mast-mounted cup anemometers. (It should be noted that the slopes
very close to unity are slightly fortuitous, since the cup anemometer measurements have
uncertainties at least of order ±1%, due to calibration and mounting/shadowing effects).
4.6.3 System positioning accuracy
Height AGL [m] Slope m R 2
116 0.993 0.977
100 0.987 0.988
80 0.984 0.992
60 0.990 0.992
40 1.007 0.992
Correct alignment ensures the risks are low, but errors in aligning the lidar during set-up will
have an impact on the measurement of wind bearing (if the lidar is rotated from its correct
orientation) and vertical wind speed (if the lidar is tilted, so that the axis of its conical scan
is not precisely vertical). For a small tilt angle δ, the error in vertical wind speed w will vary
88 DTU Wind Energy-E-Report-0029(EN)