NEXRAD
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NEXRAD or Nexrad (the next-generation radar) is a network of Doppler radars operated by the National Weather Service, an agency of NOAA, the National Oceanic and Atmospheric Administration, in the United States. NEXRAD detects precipitation and atmospheric movement or wind. It returns data which when processed can be displayed in a mosaic map which shows patterns of precipitation and its movement. The radar system operates in two basic modes, selectable by the operator: a slow-scanning "clear-air mode" for analyzing air movements when there is little or no activity in the area, and a "precipitation mode" with a faster scan time to do traditional storm tracking.
NEXRAD is a high-resolution Doppler radar with increased emphasis on automation, including use of algorithms and automated volume scans. It also goes by another designation, WSR-88D, which stands for [National] Weather Surveillance Radar, 1988, Doppler. 1988 was the year the NWS began implementing NEXRAD, which replaced WSR-74 and even WSR-57 units from 1974 and 1957 respectively.
The next improvement is likely to be polarimetric radar, which adds vertical polarization to the currently used horizontal radar waves, in order to detect exactly what is reflecting the signal back. This so-called dual polar operation allows the radar to distinguish between rain, hail and snow, while the horizontally polarized radars cannot accurately tell the difference between hail (high reflectivity) and very heavy rainfall. Rain, sleet, snow, hail, other graupel, birds, insects, and ground clutter all have different signatures in the signals, which could mark a significant improvement in forecasting winter storms and severe thunderstorms, and even in airport safety. [1] (http://www.cimms.ou.edu/~schuur/radar.html)