How Weather Radars Work

Radar, is an acronym for, RAdio Detection And Ranging. Uniquely, Doppler radar can measure wind speed in precipitating regions. A Doppler radar receiver “hears” waves of a higher frequency if precipitation particles are moving toward the radar, and a lower frequency if particles are moving away. Doppler radars identify severe weather. For example, if particles switch from moving toward and then away from the Doppler radar over a small distance, the source may be a tornado. A modern Doppler radar system consists of a large radar dish housed inside an even larger hexagonal dome to protect it from the elements. The radar dish can rotate 360 degrees in the horizontal and approximately 20 degrees in the vertical. As the radar antenna turns, it emits extremely short pulses and waits for these pulses to return during the "listening period". Each pulse lasts about 0.00000157 seconds with a "listening period" of 0.00099843 second. The transmitted radio waves move through the atmosphere at the speed of light. Once it hits a raindrop or snowflake, the radio waves are scattered with some of the energy returning back to the radar. Radar observes all of this information during the “listening period”. This process is repeated up to 1,300 times per second. Observing the time it takes the radio waves to leave the antenna, hit the target, and return to the antenna, the radar can calculate the distance and direction of the target using the “Doppler effect”. The Dopller Effect is the change in frequency of a wave for an observer moving relative to its source. In addition, the returned energy the radar receives provides information on the target’s characteristics including size, intensity and even precipitation type.