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Doppler Radar
10/21/2002
Listen in RealAudio 
Hi, I'm Bryan Yeaton with The Weather Notebook and today we're going to take a look at
something that can espy even the tiniest raindrops and snowflakes over one hundred miles away:
Doppler radar.
NSSL's first Doppler Weather Radar located in Norman, Oklahoma. 1970's research using this
radar led to the NWS NEXRAD WSR-88D radar network. NOAA Photo Library
To understand how Doppler works, you should know a bit about conventional radar. In the late
19th century, Heinrich Hertz demonstrated that metal objects reflect radio waves. By the
middle of the 20th century, meteorologists had discovered that precipitation- raindrops,
snowflakes, and hailstones - do the same thing. This allowed them to gather information about
approaching storms.
Now, Doppler radar, named after its creator Johann Doppler, takes storm detection to another
level. First of all, it transmits three or four times the number of microwaves per second than
does conventional radar. It then compares the incoming waves with the outgoing waves, looking
for a shift in the wavelength. If the storm is approaching the radar, the wavelength will be
shortened; if it's moving away, the wave will be lengthened. This is what's called "The
Doppler Effect."
By using multiple radar units, a 3-dimensional picture of a storm can be taken. The other
amazing thing about Doppler is its sensitivity. It is so sensitive that it sees not only
precipitation, but it can also see the air.
Doppler radar can even help see into the future. By looking at wind profiles, Doppler can
detect conditions that are perfect for creating tornadoes and other severe weather. By being
able to see this pre-storm environment, forecasters can issue warnings up to twenty minutes in
advance, saving perhaps dozens of lives per event.
Our website, www.weathernotebook.org, can show you more on how Doppler works. The Weather
Notebook is underwritten by Subaru with major support provided by the National Science
Foundation. Thanks today to our assistant producer, Doug Sanborn.
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