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  • Writer's pictureMichael Thornton

What is a doppler radar and how does it work?

Updated: Mar 26, 2022

History of the doppler radar

NSSL 10cm S Band radar - photo courtesy of NOAA

Christian Doppler,, date unknown

Before we can begin talking about what a Doppler radar is, we must first understand where the name and idea came from. In 1842, Christian Doppler, an Australian mathematician, discovered the Doppler effect. The Doppler effect occurs when there is a disruption in the wavelength. This change is seen when there is relative motion between the source of the wave and the object/person. The frequency is much higher when the source of the wave is moving towards an object or person and lower when the wave is slowing down. This change in pitch is what we know as the Doppler effect.

During World War II, the United States military used radars to detect enemy aircraft. They accomplished this by transmitting short pulses of radiation into the atmosphere. When the radiation detected an object it bounced back to the radar. However, when Thunderstorms or other types of precipitation were in the area, observers noticed that the radiation from the radar bounced back. Researchers began to investigate this strange phenomenon and found that these strange signals on the radar were actually precipitation being picked up by the radar and not aircraft.

Photo of a WSR-88D at sunset in Norman, OK

Because of this finding, in 1942, the U.S. Navy donated 25 radars to the Weather Bureau. (now known as the National Weather Service) This donation by the U.S. Navy was very significant as it helped transform how we understand severe weather in the modern era. In 1988 a new radar was developed. This radar became to be known as the WSR-88D or Weather Surveillance Radar, Year 1988.

How does Doppler radar work?

TOKC in Norman, OK.

The WSR-88D is seen as the most powerful and advanced Doppler radar on planet earth. All 122 WFO's (Weather Forecast Office/National Weather Service) use a WSR-88D, with over 160 WSR-88D's operational in all 50 states. Now that we have a better understanding of how Doppler radars were found, we can get into talking about how they work. Doppler radar uses radiation to be able to see what the storms are doing. This radiation leaves a 28ft antenna that is inside the dome. When the radiation strikes an object, whether that be a storm, windmill, or a group of birds, the radiation scatters into different directions and only a small amount of that radiation is sent back to the antenna. A Doppler radar will spend almost an entire hour listening for any returning radiation. Once the antenna has received a return signal, the signal is then sent into a building at the base of the radar. (brown building seen in the photo) where it is then inspected by a computer to determine the strength and time that it took for the signal to return to the antenna. The beautiful WSR-88D is able to transmit over 750,000 watts of energy. Because of the high amount of

Shelf cloud going over a WSR-88D at the Norman Radar Operations Center

energy, the radiation transmitted from the radar is able to travel for more than 285 miles away when using long-range reflectivity and 143 miles when using short-range reflectivity. However, because of the curvature of the earth, the height of the beam increases the further you are from the radar. What this means is that if a storm is very far away from the radar, the beam will be looking higher into the storm compared to if

WSR-88D at the Norman ROC

the storm was closer, where the beam will be looking into the storm at a much lower height. From 2011 until 2013 all NWS owned WSR-88D's were upgraded to Dual-Pol (Dual-Polarization). Thanks to Dual-Pol the WSR-88D is now able to determine whether a storm is producing rain, freezing rain, hail, ice, or snow because instead of the WSR-

88D sending out just a horizontal pulse of energy it also sends out a vertical pulse of energy with Dual-Pol. What this means for

Base Velocity and CC showing a damaging tornado

you is that forecasters are now able to accurately estimate the amount of rain that has fallen, which can lead to better timing for flash flooding events. This also means that forecasters are able to see the melting layer, which is very important during severe weather events, along with being able to detect tornado debris because of products like correlation coefficient. Unlike prior radars such as the WSR-57 and WSR-74, the WSR-88D allows for velocities to also be measured, thus allowing meteorologist's a chance to see if a storm is producing tornadic winds or dangerous straight-line winds.

About the writer: Michael Thornton graduated from Rose State College majoring in Emergency Management. Currently, he is the Director for Tillman County Emergency Management and is an Oklahoma Emergency Management Association member.


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