Measurements of the Doppler velocity along a circle at constant range (= constant height) within a homogeneous wind field show a sine-function like shape (Fig. 2). The Doppler velocity has ist maximum value in the down wind direction, and ist minimum in the up wind direction. The phase angle of the minimum gives the wind direction (250° in the example). Besides the horizontal wind velocity, the Doppler velocity at elevated scans depends also on the falling velocity of the scattering particles. This portion is independent of the azimuth angle and results in an negative offset of the sine curve. The offset is shown in Fig. 2 by the dashed line. The wind velocity is the amplitude of the sine curve with respect to the offset (5 m/s in the example).
Fig.1 Estimation of the wind profile with a PPI at elevation phi. r1 to r3 are different ranges from the radar.
Fig. 2 Velocity Azimuth Display (VAD) of the Doppler velocity along a circle. Shown are data points and fitted sine curve.