This Doppler effect was named after the Austrian physicist, Christian Doppler, who discovered it. The frequency of the returning signal typically changes based upon the motion of the raindrops (or bugs, dust, etc.). The ability to detect the "shift in the frequency" of the pulse of energy makes NEXRAD a Doppler radar. Computers analyze the strength of the returned radar waves, time it took to travel to the object and back, and frequency shift of the pulse. This reflected signal is then received by the radar during its listening period. A small portion of that scattered energy is directed back toward the radar. The radar emits a short pulse of energy, and if the pulse strike an object (raindrop, snowflake, bug, bird, etc), the radar waves are scattered in all directions. NEXRAD ( Next Generation Radar) can measure both precipitation and wind. In addition, the radar image will not show echos from precipitation that lies outside the radar's beam, either because the precipitation is too high above the radar, or because it is so close to the Earth's surface that it lies beneath the radar's beam. To determine if precipitation is occurring at greater distances, link to an adjacent radar.
This image will not show echoes that are more distant than 143 miles, even though precipitation may be occurring at these greater distances. The maximum range of the base reflectivity product is 143 miles (230 km) from the radar location.
Base reflectivity images are available at several different elevation angles (tilts) of the antenna the base reflectivity image currently available on this website is from the lowest "tilt" angle (0.5°). "Reflectivity" is the amount of transmitted power returned to the radar receiver after hitting precipitation, compared to a reference power density at a distance of 1 meter from the radar antenna. The Local Radar base reflectivity product is a display of echo intensity (reflectivity) measured in dBZ (decibels). Precipitation intensity is measured by a ground-based radar that bounces radar waves off of precipitation.
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