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are selected (♦page 4-26).
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OVERVIEW COLLINS
MultiScan™ Radar
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COLLINS THEORY OF OPERATION
MultiScan™ Radar Table of Contents
TABLE OF CONTENTS
Title Page
Thunderstorm Reflectivity ................................................................. 3-1
The Ideal Radar Beam ..................................................................... 3-4
MultiScan Emulation of the Ideal Radar Beam ................................. 3-5
The MultiScan Process .................................................................... 3-6
Update Rates ................................................................................... 3-7
Automatic Gain ................................................................................. 3-8
The End Result ................................................................................. 3-8
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THEORY OF OPERATION COLLINS
MultiScan™ Radar
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COLLINS THEORY OF OPERATION
MultiScan™ Radar Thunderstorm Reflectivity
THEORY OF OPERATION
THUNDERSTORM REFLECTIVITY
Understanding thunderstorm reflectivity is the key to understanding how
MultiScan works. In general, thunderstorm reflectivity can be divided
into three parts (see figure 3-1).
Figure 3-1 Thunderstorm Reflectivity Levels
The bottom third of the storm below the freezing level is composed
entirely of water and is the part of the storm that most efficiently
reflects radar energy. The middle third of the storm is composed of a
combination of supercooled water and ice crystals. Reflectivity in this
part of the storm begins to diminish due to the fact that ice crystals
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THEORY OF OPERATION COLLINS
Thunderstorm Reflectivity MultiScan™ Radar
are very poor radar reflectors. The top third of the storm is composed
entirely of ice crystals and is almost invisible to radar. In addition, a
growing thunderstorm may have a turbulence bow wave above the
visible portion of the storm (♦page 5-5).
Figure 3-2 shows an actual thunderstorm. The pictures in figure 3-3
show the corresponding radar picture as tilt is increased. In practice,
finding the proper tilt angle during manual operation often becomes
a compromise between observing the most reflective part of the
thunderstorm and reducing ground clutter returns (♦page 4-61, ♦page
5-6).
Figure 3-2 Observed Thunderstorm
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COLLINS THEORY OF OPERATION
MultiScan™ Radar Thunderstorm Reflectivity
Figure 3-3 Observed Thunderstorm and Corresponding Radar
Display at Varying Tilt Settings
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THEORY OF OPERATION COLLINS
The Ideal Radar Beam MultiScan™ Radar
THE IDEAL RADAR BEAM
Understanding thunderstorm reflectivity and the effect that radar tilt
angle has on it allows us to envision a hypothetical ideal radar beam
for weather threat detection. The ideal radar beam would look directly
below the aircraft to detect building thunderstorms and then follow the
curvature of the earth out to the radar’s maximum range (figure 3-4).
Thus, the ideal beam would keep the reflective part of all significant
weather in view at all times, from right at the aircraft out to 320 NM.
Figure 3-4 Ideal Radar Beam
N NOTE
Note that the earth’s curvature causes a drop of approximately
65,000 feet over a distance of 320 nautical miles.
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COLLINS THEORY OF OPERATION
MultiScan™ Radar MultiScan Emulation of the Ideal Radar Beam
MULTISCAN EMULATION OF THE IDEAL
RADAR BEAM
MultiScan emulates an ideal radar beam by taking information from
different radar scans and merging the information into a total weather
picture. Rockwell Collins’ patented ground clutter suppression
algorithms are then used to eliminate ground clutter. The result is the
ability for flight crews to view all significant weather from 0 to 320 NM
on a single display that is essentially clutter free (figure 3-5).
Figure 3-5 MultiScan Emulation of Ideal Beam
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THEORY OF OPERATION COLLINS
The MultiScan Process MultiScan™ Radar
THE MULTISCAN PROCESS
Figure 3-6 illustrates the MultiScan process. Two scans are taken, each
optimized for a particular region in front of the aircraft. In general, the
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Collins Weather Radar operator’s guide(9)
