Average wind speed increases as the elevation rises meter by meter and reduces the braking effect of hills, vegetation and other ground-based barriers. For this reason, state-of-the-art wind power systems now have hub heights of between 120 meters and 160 meters. The rotary blades that are 70 meters to 100 meters long jut more than 200 meters into the sky at their highest point. This creates a problem for planners: Wind measurement towers are generally 100 meters high.
Doppler LiDAR systems are used to precisely measure air movements at higher elevations. The ground-based measurement devices shoot laser beams into the sky. These beams hit particles and aerosols in the air, a process that reflects the light. Measurement heights can be calculated from this duration period. The systems can determine wind speeds and direction with the help of the Doppler shift that causes the movement of the backscattering particles.
At times, wind farm operators will measure the wind in front of running turbines and use the LiDAR process horizontally. The measuring devices are set up on the turbines and measure air movements that occur up to a distance of several hundred meters in front of the rotor with the help of several laser beams. The results are used to more precisely position the turbines in the wind. They also help optimize operations in terms of increased yields and reduced stress on the units because the LiDAR-based control system can proactively react to wind gusts and turbulence.
Incidentally, the ESA research satellite Aeolus also uses LiDAR technology to produce wind profiles. It circles the Earth at an altitude of 320 km and shoots short pulses of UV light at the Earth’s surface. A telescope collects the light scattered by aerosols, evaluates the duration of the pulses and the frequency—and produces wind profiles from the surface to an altitude of 30 km on the basis of this information.