Figure 1: Low troposphere wind profiler radar CFL-08 of the Chinese company BIRM
A Wind Profiling Radar or (WPR) Wind Profiler is a radar operating mostly in the UHF band and radiating vertically upwards. It is used to measure the vertical profiles of wind speeds. In a clear atmosphere, they receive the reflected power due to irregularities in the refractive index of the air caused by turbulence. The frequency of the reflected power is changed by the Doppler effect depending on the radial speed of the wind. From several measurements with slightly different radiation angles, the real wind speeds can be calculated as three-dimensional wind vector.
With a carrier frequency of 400 to 500 MHz, height ranges of up to 15 km can be reached (stratosphere), higher frequencies between 1 … 1,3 GHz only up to 5 km (lower troposphere). Horizontal phased array antennas are used to electronically control this fast change of direction. The transmission power is in the lower kilowatt range, so it can be easily achieved with solid-state transmitters. The routine wind measurement is based on the DBS method with three to four directions at angles approximately 15° from the zenith. To derive the wind vector, it is assumed that the (mean) wind field in the sampled volume is stationary and horizontally homogeneous, therefore the measurement results are averaged over 30 minutes.
All these radar sets are mostly remote controlled and can be used unattended even in outlying areas. In contrast to optical methods (laser or lidar) they are able to measure through clouds and fog. They can be used in continuous operation and can therefore continuously document wind speeds. The data generated by wind profilers are incorporated into the numerical weather forecast models.