Doppler radar is a weather radar that not only senses the size and distance of raindrops, snowflakes and ice pellets, it also detects their movement.
The radar gets its name from scientist Christian J. Doppler, who first described the principal employed by the radar in 1853. Doppler noticed that the whistle from a passing train changed pitch. He reasoned that sound waves moving toward a fixed point arrive at a different frequency than sound waves moving away.
Doppler radar applies this principal, detecting changes in frequencies reflected from precipitation to determine its movement and speed. In effect, the radar is able to measure the wind by determining how fast rain is being pushed along. These days, Doppler radars can detect even fine differences in wind speed and direction over relatively small areas, which has become a key component in the modern detection of severe storms and tornadoes.