A remote-sensing device that transmits and receives microwave radiation for the purpose of detecting and measuring weather phenomena. Radar is an acronym for radio detection and ranging. Today, many types of sophisticated radars are used in meteorology, ranging from Doppler radars, which are used to determine air motions (for example, to detect tornadoes), to multiparameter radars, which provide information on the phase (ice or liquid), shape, and size of hydrometeors. Airborne Doppler radars play a vital role in meteorological research. Additionally, weather radar is now orbiting the Earth on the NASA Tropical Rainfall Measuring Mission satellite, launched in November 1997. Radars are also used to detect hail, estimate rainfall rates, probe the clear-air atmosphere to monitor wind patterns, and study the electrification processes in thunderstorms that generate lightning discharges.