training course on weather radar systems - RTC, Regional Training ...

MODULE A- INTRODUCTION TO RADAR
(Doppler filter bank to cover the Doppler spectrum) are used rather than a simple MTI
system described above, in order to cancel clutter and to extract the Doppler frequency
and amplitude components of the received signal.
By extracting the Doppler characteristics of signals it is possible to achieve much better clutter
cancellation than in conventional radars, and the target’s radial velocity component can be
calculated once the Doppler frequency is measured, in addition it is possible by range gating to
measure the Doppler and the amplitude of the returned signal in each radar cell. The location of
the radar cell by measuring the return time, the position of the antenna (azimuth and elevation) at
the time the signal in the radar cell was received. All this processing is done digitally. A simple
block shows the essential components of the Pulse Doppler Radar that is used for weather
observation.
4.11. Weather Radars
Although these names refer to the application of radar, there is a significant difference in the type
of radar that is used which is worth to be illustrated. In general radars measure the location of a
target that is range, azimuth and height. The major distinction between meteorological radar and
other kinds of radars lies in the nature of the targets. Meteorological targets are distributed in
space and occupy a large fraction of the spatial resolution cells observed by the radar. Weather
radars are pulsed radars with Doppler capability. So we can call them as Pulsed Doppler Weather
Radars. Weather radars can operate in different frequency bands. So a classification can be made
based on the frequency band as follows:
L band radars
Those radars operate on a wavelength of 15-30 cm and a frequency of 1-2 GHz. L band radars
are mostly used for clear air turbulence studies.
S band radars
Those radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the
wavelength and frequency, S band radars are not easily attenuated. This makes them useful for
near and far range weather observation. It requires a large antenna dish and a large motor to
power it. It is not uncommon for an S band dish to exceed 25 feet in size.
TURKEY RADAR TRAINING 1.0 / ALANYA 2005 39