Meteotest SODAR
The SODAR technique is based on acoustic pulses emitted into the atmosphere. The reflected signal is converted into wind speed and direction values.
Wind speed and direction are measured from 15 to 200 m above ground - a big advantage in contrast to measurements on masts, which record wind speed often far below hub height. Extrapolations of wind speeds measured on a mast to hub heights of wind turbines are tricky, especially in complex terrain.
Supplementary SODAR measurements determine the vertical wind shear and avoid incorrect extrapolations. SODAR is very easy to install and spares erecting an expensive high mast to measure wind speeds at hub height.