The phase 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 phase' of the pulse of energy makes the WSR-88D a Doppler radar. The remaining 59 minutes and 53 seconds are spent listening for any returned signals. 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 WSR-88D spends the vast amount of time 'listening' for returning signals it sent.

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. These 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 signal is then sent to a computer system located in a small building at the base of the radome. The reflected signal is then received by the same antenna that sent the signal, during its listening period. A small fraction of that scattered energy is directed back toward the radar. If the energy strikes any object (rain drop, snow, hail, bug, bird, dust, etc), the energy is scattered in all directions (blue). The radar emits a burst of energy (green), from a 28 foot diameter antenna inside the radome (the white, soccer ball covering). The WSR-88D obtains weather information (precipitation and wind) based upon returned energy generated and received at the Radar Data Aquisition (RDA) unit (see animated diagram below). That's about 3 elevations per minute, or one radar image every 20 seconds! What other operational weather radar can do that? How does the radar work? During severe weather, the NWS WSR-88D is looking at 14 different elevations every 5 minutes, generating a radar image of each elevation. Many other radar systems do not have this kind of power, nor can they look at more than one 'slice' of the atmosphere. It also allows energy to continue past an initial shower or thunderstorm near the radar, thus seeing additional storms farther away. The WSR-88D is considered by many to be the most powerful radar in the world, transmitting at 750,000 watts (an average light bulb is only 75 watts)! This power enables a beam of energy generated by the radar to travel long distances, and detect many kinds of weather phenomena. The NWS Northern Indiana radar began warning operations on March 17th, 1998. The WSR-88D has also been installed in Puerto Rico and several islands in the Pacific. Since first being built and tested in 1988, it has been installed and used operationally at over 160 locations across the United States, including Alaska and Hawaii. The WSR-88D is one of the most powerful and advanced Weather Surveillance Doppler Radar in the world. How does the radar work? Is every thing I see on the images an accurate picture of my weather? What are the different types of radar images? How often are the images updated? What is Clear Air Mode? What is Precipitation Mode? What do the colors mean in the reflectivity products? What is the difference between base and composite reflectivity? What is UTC Time? Everything You Ever Wanted to Know about the NWS WSR-88D

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