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 NEXRAD a Doppler radar. Learn about the different scanning modes of the Radar here 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. NEXRAD 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!

Computers analyze the strength of the returned pulse, time it took to travel to the object and back, and phase, or doppler shift of the pulse. This reflected signal is then received by the radar during its listening period. Note: it's a small fraction of the emitted energy that is scattered directly back toward the radar. If the energy strikes an object (rain drop, snowflake, hail, bug, bird, etc), the energy is scattered in all directions (blue). The radar emits a burst of energy (green in the animated image). NEXRAD (Next Generation Radar) obtains weather information (precipitation and wind) based upon returned energy.

Weather radar weather underground