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How NEXRAD works
WSR-88D weather surveillance radar or NEXRAD (NEXt generation RADar) is a doppler radar system that has greatly improved the detection of meteorologic events such as thunderstorms, tornadoes and hurricanes. An extensive network of NEXRAD stations provides almost complete radar coverage of the continental United States, Alaska, and Hawaii. The range of each NEXRAD is 124 nautical miles.
| NEXRAD stations in the continental U.S. with their coverage ranges |
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The word radar is an acronym for "RAdio Detection And Ranging". Radars transmit microwave signals into the atmosphere and then listen for return signals. If the transmitted signal intercepts an object, most of the energy is scattered, but some will be reflected back to the radar receiver. The quantity that a radar measures is the returned energy, which is converted to a quantity called reflectivity. The amount of reflected energy can be used to estimate the number or density of targets in the atmosphere. Because microwaves travel through air at a known velocity, time between transmission and reception of the reflected energy can be used to estimate the distance of a target from the radar. Reflectivity is often represented by the symbol "z." NEXRAD displays measures of reflectivity in dBZ or decibels, that are represented as different colors on the radar image.