Abstract :
Radar is an
acronym for Radio Detection And Ranging. A radar is an electro-magnetic device capable
of transmitting a electro-magnetic wave near 1 Ghz, receiver back a reflection from
a target and based on the characteristics of the returned signal determine things
about the target. Radars have become indispensable in several major fields of research
and in commerce.
The Federal
Aviation Agency (FAA) makes extensive use of radars not only to track aircraft,
but to make sure landings and take-offs are uneventful. Meteorologist use radars
to track severe weather and to estimate the amount of rainfall. Radar meteorology
means many things to many people. Depending on what your research interests is your
definition may be very different from mine. As a working definition I will use the
following.
What is Radar
Radar meteorology
is the study of the atmosphere using radar as a tool.Radar Meteorology is not a
true branch of meteorology because it is use by several true branches of meteorolo
gy, such as cloud physics and severe storms, as a tool for that particular branch.
Radar meteorology
is also not a branch of radio meteorology; Radio meteorology is the study of how
electro-magnetic waves travel through the atmosphere. As such radio meteorology
deal with refraction, reflection and propagation of electro-magnetic waves. Although these
concepts are very important they are not the core of radar meteorology.
Characteristics
Radar is a remote
sensing tool in that it is not in contact with the object it is sensing Radar measures
the characteristics of the atmosphere from a distance. Further, radar is an active
sensor in that it modifies the atmosphere and then measures the atmospheres response.
Radar is not
a prognosticator, i.e. it does not make a forecast rather it samples the atmosphere
from a close distance and there appears to make a very accurate forecast. Radar
is a means of detecting locating identifying, measuring and then displaying the
atmosphere and what is in it. Radar is useful because of the following characteristics:
1. Radar scans a three-dimensional volume and can
be pointed any where in space. The scale of the smallest volume is meso-a.
2. Continuous scanning in space Typically with 5 ->
8 minutes between scans of the same volume.
3. Reasonable resolution. For a typical 2 msec pulse
at 100 nm the volume is about 5 km x 5 km x 600m
4. Total variability
of the atmosphere can be measured, i.e. Radar can measure all the components of
the total derivative.
5. Radar can make in-storm measurements
6. Radar can measure the actual severity
of the storm, since Ze is a measure of the
number of hydrometers per cubic unit.
7. Radar, if coherent, can measure the three components
of the wind.
Thus from the
meteorologists point of view a radar provides a large number of advantages over
any other tool designed to look at the structure of severe storms and clouds. Much
of what we know about the inner workings of thunderstorms and other precipitating
cloud systems come from radar.
Radar uses an
antenna producing a narrow beam of energy to scan a volume of space until a reflection
is obtained. The direction the antenna is pointing and the time interval between
the transmission and reception determine the location of the reflection in space.
Further the strength and polarization of the reflection determine the characteristics
of the target.
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