The Doppler radar is a device that measures the Doppler shift in a radar beam reflected from an object's motion towards or away from the radar aerial. This so-called 'Doppler-effect' is used in meteorological radars where the objects are water droplets on either side of a rotating mesocyclone, thunderstorm or tornado.
Angular velocity can be calculated from the extent of the red shift on one side and blue shift on the other. This technology is used for the meteorological NEXRAD (Next Generation Radar) system to measure both, simple precipitation patterns and the severity of thunderstorms or the likelyhood of tornado development.
Related links:
WeatherOnline Radar
