Doppler radar
Doppler radar uses the Doppler effect to measure the speed (radial velocity) of targets. Radial velocity is how fast the target is coming towards, or going away from, the radar. The Doppler effect will shift the received frequency up or down, based on the radial velocity of a target in the beam. This gives a direct and highly accurate measurement of target velocity, but only the radial velocity. Doppler radar by itself doesn't measure the azimuthal velocity (how fast it is going in other directions).
Doppler radars may be Coherent Pulsed, Continuous Wave, or Frequency Modulated.
Doppler Radar Media
U.S. Army soldier using a radar gun, an application of Doppler radar, to catch speeding violators.
The emitted signal toward the car is reflected back with a variation of frequency that depend on the speed away/toward the radar (160 km/h). This is only a component of the real speed (170 km/h).
AN/APN-81 Doppler radar navigation system, mid-1950s
The US Weather Bureau's first experimental Doppler weather radar unit was obtained from the US Navy in the 1950s
Doppler navigation system in the National Electronics Museum
