Radar was NOT invented to detect weather. Among its' first uses was during World War II. Radar units in England (United Kingdom / Great Britian) were able to get advance warning of Nazi air strikes during the Battle of Britain. They noticed that when it rained the radar screens were covered in a gray haze...and planes could not be detected! While scientists tried to get around the problem, weather forecasters quickly saw the advantages of the new invention! Weather radar was born!

Radar works by sending out a radio wave at a very high frequency. When the radio signal hits raindrops part of the signal bounces back to the radar. The signal travels at the speed of light (over 350,000 kilometers per second!).

Knowing exactly how fast the signal is traveling, means that we can tell how far away the rain is by timing how long it takes for the signal to travel to the rain and then bounce back to the radar. This happens so fast that most radars send out about 1000 signals (called pulses) each second!!

Doppler Radar:

Doppler radar can not only see rain and other forms of precipitation. It can see the winds inside storms. In some cases it can even track birds, bugs and dust particles and tell a forecaster what the winds are doing in areas where there is no rain.

When tornadoes develop they blow rain drops around in a circle.

Doppler radar can see the raindrops going in different directions and tell a forecaster precisely where the tornado is in some cases.

HOW DOPPLER RADAR WORKS:

Have you ever listened to a train whistle as it was coming toward you? Did you notice that the pitch of the whistle changes as it passes you and starts moving away? This change in the frequency of the sound is called the Doppler Effect. Doppler radar measures the very small changes in the frequency of the signals it receives to see determine winds. The radar can only see wind coming toward it or moving away from it, though.

NEXRAD

The National Weather Service has a network of Doppler radars. These radars have allowed forecasters to give much better warnings of severe storms and tornadoes.   The image on the right shows what forecasters  saw just before the town of Greensburg Kansas was leveled by an EF5 tornado. The blue is wind coming toward the radar and red is wind going away. Notice the very strong wind showing up just south of Greensburg. A new type of radar called Dual Polarimetric Radar is now being used in some cities. It can see the shape of the rain, snow and hail in a storm. These new radars will be installed by the National Weather Service in a few years. The TV station where I work (WHNT TV) was the first one in the world to have a Dual Polarimetric Radar. We built it in conjunction with researchers at The University of Alabama. It is called ARMOR. This stands for Advanced Radar for Meteorological Operations and Research. Follow the links to learn more about ARMOR and Dual Polarimetric Radar research.

Overview of the Doppler Radar System

Radar Tutorial

What does Dual Polarimetric Radar measure?

Greensburg, Kansas = May 2007

Dual Pol Examples

ARMOR Radar

Learning Activities
	WSR-88D (NEXRAD)Terms & Acronyms (NEXRAD = Next Generation Radar)
	RADAR-ology
	Radar Meteorology - online guide

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