| MadSci Network: Physics |
Mark,
"RADAR" is short for "Radio Detection and Ranging", so a system
such as this emits radio waves. Simple RADAR systems use a
directional antenna which emits short carrier wave pulses toward
a target. The interval between which the pulse is emitted and
the reflection is received gives the distance. This is because
(as you might already know) radio waves travel at the speed of
light (186,000 miles per second).
Modern Air Traffic Control RADAR uses a digitally encoded pulse
which (along with indicating the range) also activates a
transponder radio in the airplane. It will then reply to the
system on the ground with certain information such as the airline,
flight number and altitude, so that controllers can give the
appropriate guidance.
One new type of RADAR system is called "Doppler", and can indicate
if a target (such as a cloud) is approching or moving away, and at
what speed. This is very useful for detecting severe weather,
tornadoes, etc. By using this type of RADAR and combining it with
computer technology, the National Weather Service can create a three
dimensional image of the interior of a storm.
Another type of RADAR is called "Synthetic Aperture" and can be used
to make three dimensional images of things like the surface of the
Earth, the other planets, moons, asteroids, etc.
As you can see, RADAR can be a complex subject, but is actually based
on a very simple principal: electromagnetic waves.
For more information regarding this subject, check out the following:
The history of RADAR at MIT:
http://graupel.mit.edu/radar_at_mit.html
The MIT Weather RADAR Lab Home Page:
http://www-cmpo.mit.edu/Radar_Lab.html
The NASA/JPL Imaging RADAR Home Page:
http://southport.jpl.nasa.gov/
I hope this help, and happy surfing!
Keith Little
gklittle@sprintmail.com
Try the links in the MadSci Library for more information on Physics.