I understand the basics of radar and Doppler shift. But how do meteorologists use radar to track storms? What is solid that bounces back radio waves? Can you tell if there's lightning in the storm?
All weather radars send out radio waves from an antenna. Objects in the air, such as rain drops, snow crystals, hail stones or even insects and dust, scatter or reflect some of the radio waves back to the antenna. All weather radars, including Nexrad, electronically convert the reflected radio waves into pictures showing the location and intensity of precipitation.
A: H.N. Shirer, a meteorology professor at Penn State University, says an instrument akin to a radio receiver is used to gather lightning data. This receiver is tuned to the frequency of radio waves produced by lighting bolts. It measures how fast the signal goes from zero to a significant number. Lighting bolts have a characteristic signature that lies in the electric and magnetic fields of each bolt that create the radio waves. To pinpoint the position of a lightning strike, four receiving sites are used. The data collected at each site is compared and analyzed and ultimately the magnitude of the signal or the strength of the signal is used to help determine the location, time of strike, and intensity of the bolt. Other signatures of the strike are used to differentiate between cloud to ground and cloud to cloud strikes.
[This message was edited by frankvan on 07-09-02 at 01:36 PM.]
One of the main differences between doppler radar and other radars is the EDAC circuit (error detection and correction). There are a few different types of EDACs, this one is commonly used. The returned "echos" received by the radar antennas are checked against the very next consecutive echo for variations. Echos that are not identical are shunted to ground and never viewed.
The reason for the circuit is the interferance common in weather patterns. Clearing out the bad stuff makes a doppler radar much more accurate in tracking atmospheric changes. (The correction circuit is fast enough that you'll never see it removing random echos.)
Another difference, and the reason for the radar's name, is that the echos also sometimes return to the antenna on a slightly aschew frequency. The radar itself might put out a constant 4 gigahertz, but the returns will come back a little higher or a little lower.
The frequencies are altered due to the doppler affect, meaning that moving objects affect the wavelength of radio signals. The radar receiver can read the variation in the frequency and determine whether a weather system is moving in or moving away, how far away it is, and how fast it's moving.
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