Radar is an acronym for 'radio detection and ranging'. Radars, which are equipment used to detect and measure the distance to a target via radio waves, can be classified by the type of radio waves used and the information that can be obtained. Conventional radars, such as those used by the Japan Meteorological Agency, measure only the amplitude information of the radio waves which have back-scattered from raindrops and returned to the radar (reflectivity factor), and with which rain rates can be estimated. Doppler radars, in operation as airport radars, measure frequency information (Doppler frequency) in addition to the amplitude information, from which the radial velocity (Doppler velocity) of raindrops to the radar can be measured. Multi-parameter radars enable the transmission of two types of radio waves; vertical and horizontal polarization, while conventional and Doppler radars can transmit only a single type. Various parameters can be obtained from the signals that are reflected from raindrops. The use of multi-parameter radar enables accurate rainfall estimates, as polarization parameters are closely related to raindrop shape and their drop-size distribution. Further, distinctions can be made such as that between rain and snow.

Radar types / information that can be obtained.