Radartutorial .eu
Radial Speed
Figure 1: Speed vectors of an airplane into reference to the radar site
The radial speed of an airplane to the radar unit is the part of the speed of the airplane, this one pointing to the radar site or in the direction of the radar away. The vector of the tangential speed is vertically by this.
If an airplane flies past on an even course at the radar unit, it comes to a point, the radial speed is zero here and the tangential speed is equal for the really speed of the airplane. Therefore the Doppler- frequency of the airplane is equal zero.
At further straight ahead course the vector of the radial speed shows to the radar unit away, it is a negative speed. A negative Doppler-frequency also arises here, but not making any panic: It is exactly as large as the positive Doppler-frequency. (Because it is the difference between the received signal and the transmitted signal, this one Doppler-frequency has got a by 180° revolved phase relationship only.)
Well, if an airplane flies around the radar unit in a circle course, then the radial speed is permanently zero. No Doppler-frequency arises and the airplane is calculated by the MTI filter as a ground clutter and this target isn't shown on the scopes.
