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Remote Sensing
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Radar Basics
  radar signals
  wave properties
> signal scattering
  wavelength effects
  ray paths
  clear air returns
  target location
  scanning modes
  radial velocity

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Scattering of a Radar Pulse
by a target back to the receiver

When a pulse encounters a target...
it is scattered in all directions. Of interest is the signal component received back at the radar. This signal is typically much weaker than the original sent from the transmitter and is called the "return signal".
The larger the target, the stronger the scattered signal.

The more targets there are to scatter the pulse, the stronger the return will be because the return signals from each target combine to produce a stronger signal. This means that many large raindrops will produce a stronger return than a few small raindrops. The quantity that a radar measures is the returned power which, with knowledge of other radar characteristics, is converted to a quantity called the reflectivity factor, or more simply, the "reflectivity".

The magnitude of the reflectivity is related to the number and size of the drops encountered by the electromagnetic pulse. For this reason, high reflectivity generally implies heavy precipitation while low reflectivity implies lighter precipitation. Plots of the radar reflectivity, typically using colors to depict its magnitude, show both the location and intensity of precipitation. Extremely high reflectivities often indicate hail.

wave properties
Terms for using data resources. CD-ROM available.
Credits and Acknowledgments for WW2010.
Department of Atmospheric Sciences (DAS) at
the University of Illinois at Urbana-Champaign.

wavelength effects