Environmental Engineering Reference
In-Depth Information
Figure 1: Propeller anemometer in fi xed three-dimensional arrangement.
thus to an under-estimate of the wind speed. If propellers are mounted in a fi xed
arrangement the under-estimate of the wind speed is even more signifi cant as the
axis of the propeller is not aligned with the wind direction.
2.2.5 Remote sensing
An alternative to mast-mounted anemometry are ground-based remote sensing sys-
tems. Two systems have found some acceptance in the wind energy community:
Sodar and Lidar. Both the Sodar (SOund Detection And Ranging) and the Lidar
(LIght Detection And Ranging) use remote sensing techniques based respectively
on sound and light emission, in combination with the Doppler effect. The signal
emitted by the Sodar is scattered by temperature fl uctuations while the signal emit-
ted by a Lidar is scattered by aerosols. In contrast to the very small measurement
volume of a cup anemometer, both remote sensing devices measure large volumes,
which change with height. Both types require signifi cantly more power than a cup
anemometer making the use of a generator necessary (for the majority of models)
if no grid is available.
2.2.5.1 Sodar
Different types of Sodars are available with different arrangements of the loud-
speaker and receiver. Most commonly the sound pulse generated by a loudspeaker
array can be tilted by electronically steering the array to different directions (phased
array Sodar). The combination of three beams, one in the vertical direction and
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