Honeywell Primus 880 Pilot's Manual page 88

PRIMUSr 880 Digital Weather Radar System
Honeywell has incorporated attenuation compensation that adjusts
the receiver gain by an amount equal to the amount of attenuation.
That is, the greater the amount of attenuation, the higher the receiver
gain and thus, the more sensitive the receiver. Attenuation
compensation continuously calibrates the display of weather targets,
regardless of the amount of attenuation.
With attenuation compensation, weather target calibration is
maintained throughout the entire range of a single cell. The
cell behind a cell remains properly calibrated, making proper
calibration of weather targets at long ranges possible.
Cyan REACT Field - From the description of attenuation, it can be
D
seen that high levels of attenuation (caused by cells with heavy
rainfall) causes the attenuation compensation circuitry to increase
the receiver gain at a fast rate.
Low levels of attenuation (caused by cells with low rainfall rates)
cause the receiver gain to increase at a slower rate.
The receiver gain is adjusted to maintain target calibration. Since
there is a maximum limit to receiver gain, strong targets (high
attenuation levels) cause the receiver to reach its maximum gain
value in a short time/short range. Weak or no targets (low
attenuation levels) cause the receiver to reach its maximum gain
value in a longer time/longer range. Once the receiver reaches its
maximum gain value, weather targets can no longer be calibrated.
The point where red level weather target calibration is no longer
possible is highlighted by changing the background field from black
to cyan.
Any area of cyan background is an area where attenuation has
caused the receiver gain to reach its maximum value, so further
calibration of returns is not possible. Extreme caution is
recommended in any attempt to analyze weather in these
cyan areas. The radar cannot display an accurate picture of what
is in these cyan areas. Cyan areas should be avoided.
NOTE: If the radar is operated such that ground targets are
affecting REACT, they could cause REACT to provide
invalid indications.
Any target detected inside a cyan area is automatically forced to a
magenta color indicating maximum severity. Figure 5- 28 shows the
same storm with REACT OFF and with REACT ON.
Radar Facts
5-38
A28- 1146- 102- 00