Musketeer I experiment 2007

The Musketeer Experiment:: 3-D Lidar vs. 3-D sonic wind measurements at 78 m height


Picture from Test Centre Høvsøre in 2007

n December 2007 a first test of 3-D remote sensed wind components were performed at the Risø DTU’s test station “Høvsøre” for large wind turbines, Western Jutland. Measurements of the winds three components were recorded at the 78 meter level from an in-situ meteorological tower, and several lidars, including a single QinetiQ CW prototype lidar (lower left corner) and three pulsed Windcubes were pointed to a measurement volume near the top-mounted sonic at 78 meters above ground.

Lidar measurement ranges were preset to ~138 meters for the two slant-angle pointing lidars (both pulsed and CW), while a third (pulsed Windcube) was positioned at the base of the met-tower and pointed vertical towards the test measurement volume at ~78 meters height.
For wind energy research in particular and for micro-meteorology in general we are interested in measuring turbulence, not just its statistics, but rather its gusty coherent time series of the fluctuating three-dimensional velocities at high resolution spatially and temporally. During the MusketeerEx 2007 we succeeded to point three pulsed lidars and one CW lidar towards the same small Measurement volume to measure 3-D turbulence from a single point 78 meters above the ground. Then the WindScanner becomes fully operational with respect to two angular and one focal ranging each, it is our intention to steer the beams around the wind turbines engulfing volumes as depicted by a graphical designer (Lynge Grafik) in figure 1.

Figure 1. Danish artists view on the 3-D WindScanner in operation at the Høvsøre Wind Turbine Test site.
The green rays represent the pulsed lidar’s while the red beams depict the CW pulsed laser beams. The
laser beams are seen to be steered towards the same measurement volumes, hence measuring the full
3-D wind vectors in several points (up to 500 measurement points) per second. The graphical view of the
set-up has been published in Ingeniøren, December 12th, 2007 


During MusketeerEx 2007 we recorded wind speeds up to 21 m/s. Details about the experimental
setup is given elsewhere. A small fraction (10-min) of the lidar vs. in-situ measurements are shown in figure 2, where time series of wind speeds measured by three Windcubes along with simultaneous in-situ sonic measurements at 78 m height are shown. If n is a unit vector in the direction of a lidar beam and u is the wind vector measured by the sonic, then shown is n · u. The sonic speeds have been block averaged over 1.5 s corresponding to the sampling rate of the lidar. Each wind speed determination by the lidar is based on Doppler spectra averaged over 0.5 s. The agreement between the sonic and the lidar wind components are seen to be astonishing identical! Detailed analysis of the wind traces coherence and spectral contents are ongoing.

  Figure 2. First 3-D Lidar
WindScanner measurements compared with in-situ (Sonic)
measurements at 78 meters height during the Musketeer Experiment at Høvsøre, Dec. 2007 ten minute period of wind data (Dec 8. 02:50 – 03:00). The red curve is the three-dimensional sonic data projected onto the direction of the beam of Windcube 1. The data from this lidar are shown in cyan. Likewise, the projected sonic speed and the corresponding Windcube 2 speed are shown in green and magenta. For Windcube 3 it is blue and yellow.