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HOW RADAR WORKS COLLINS
Radar Beam Characteristics MultiScan™ Radar
Figure 6-24 Effects of Radar Beam Attenuation on the Radar Display
SENSITIVITY TIME CONTROL (STC)
Sensitivity Time Control (STC) is designed to compensate for beam
attenuation within 80 NM of the aircraft. Essentially, STC increases
receiver sensitivity over time (see figure 6-25) so that more distant
thunderstorm cells have more energy on the target than do cells closer
to the aircraft. In the past, if two identical cells were seen by radar at
different ranges, the closer cell would appear more intense than the
more distant cell due to attenuation (♦page 6-23). However, STC allows
the radar to compensate for attenuation and accurately see and display
more distant targets. The end result is that targets within 80 NM of
the aircraft should be displayed accurately (accurate color levels) and
target intensity should not increase as the aircraft approaches the cell
(figure 6-26) unless the cell is actually a building thunderstorm and is
growing in intensity (see figures 6-27).
1st Edition, 1st Revision
6-24 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar Radar Beam Characteristics
Figure 6-25 Receiver Sensitivity versus Target Distance
Figure 6-26 STC Weather Compensation for Two Identical Cells
1st Edition, 1st Revision
18 Sep 03 6-25
HOW RADAR WORKS COLLINS
Radar Beam Characteristics MultiScan™ Radar
Figure 6-27 STC Weather Radar Display Compensation
Sensitivity Time Control provides highly accurate weather returns within
80 NM of the aircraft. For this reason, and reasons explained earlier
(♦page 6-23), it is recommended that only weather targets within 80
NM of the aircraft be evaluated for possible threats to the aircraft. For
weather targets that appear at ranges beyond 80 NM, the radar should
be used primarily for strategic weather planning.
LONG-RANGE COLOR ENHANCEMENT
Long Range Color Enhancement compensates for beam attenuation for
ranges from 80 to 320 NM. Essentially, Long Range Color Enhancement
estimates the amount of attenuation that has occurred and adjusts the
color levels to compensate. For instance, a thunderstorm detected
at 300 NM will appear green due to the amount of attenuation that
occurs at extended ranges. However, a cell detected at this range has
significant vertical development and a red core. Therefore, Long Range
Color Enhancement changes the return to red. However, a red return
1st Edition, 1st Revision
6-26 18 Sep 03
COLLINS HOW RADAR WORKS
MultiScan™ Radar Radar Beam Characteristics
by itself would not look like a traditional weather return, so Long Range
Color Enhancement also adds a yellow and green border within the
return to more closely emulate normal weather colors. For this reason,
weather detected at long ranges will tend to grow as it approaches the
aircraft because there is less attenuation and the radar beam is able to
more clearly detect the true color levels and size of the storm.
Figure 6-28 Long Range Color Enhancement Display
PATH ATTENUATION (RADAR SHADOW)
When intervening rainfall becomes heavy the radar beam may be so
severely attenuated that there is not enough energy to penetrate the
weather, see what is behind, and then return to the aircraft (see figure
6-29). When this situation occurs, weather behind the intervening
rainfall will be masked. This area of hidden weather is often referred to
as an area of radar shadow.
1st Edition, 1st Revision
18 Sep 03 6-27
HOW RADAR WORKS COLLINS
Radar Beam Characteristics MultiScan™ Radar
Several characteristics of the displayed weather may give clues to
attenuated areas. In figure 6-29, the display shows a normal green,
yellow and red pattern on the front side of the thunderstorm. However,
the backside of the storm shows red and yellow and no green. The
concave shape on the back of the storm also points to a possible area
of severe attenuation. Finally, the absence of ground clutter behind the
cell is a third indication that the area behind this cell may be an area of
radar shadow.
In order to evaluate the area behind the storm, lower the tilt until
significant ground clutter appears on the display. If there is clutter to the
right and left sides of the thunderstorm, but the area behind the cell
remains black, then the radar beam has experienced severe attenuation
in this region and a radar shadow exists.
Figure 6-29 Weather Display with Radar Shadow
The following picture sequence (figure 6-30) shows an aircraft
penetration of a line of thunderstorms that is causing radar attenuation.
　
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本文鏈接地址：Collins Weather Radar operator’s guide(39)