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.........SEVERE WEATHER MAP.....

How does the radar work? NEXRAD (Next Generation Radar) obtains weather information (precipitation and wind) based upon returned energy. The radar emits a burst of energy (green). If the energy strikes an object (rain drop, bug, bird, etc), the energy is scattered in all directions (blue). A small fraction of that scattered energy is directed back toward the radar. This reflected signal is then received by the radar during its listening period. Computers analyze the strength of the returned pulse, time it took to travel to the object and back, and phase shift of the pulse. This process of emitting a signal, listening for any returned signal, then emitting the next signal, takes place very fast, up to around 1300 times each second. NEXRAD spends the vast amount of time "listening" for returning signals it sent. When the time of all the pulses each hour are totaled (the time the radar is actually transmitting), the radar is "on" for about 7 seconds each hour. The remaining 59 minutes and 53 seconds are spent listening for any returned signals. The ability to detect the "shift in the phase" of the pulse of energy makes NEXRAD a Doppler radar. The phase of the returning signal typically changes based upon the motion of the raindrops (or bugs, dust, etc.). This Doppler effect was named after the Austrian physicist, Christian Doppler, who discovered it.

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