Radar Reflectivity; Weather Display Calibration - Telephonics RDR-1600 Pilot's Manual

Theory of Operation (Cont.)

5.4 RADAR REFLECTIVITY

What target will reflect the radar's pulses and thus be displayed on the
indicator?
Only precipitation (or objects more dense than water such as earth or solid
structures) will be detected by an X-band weather radar. Therefore,
weather radar does not detect clouds, thunderstorms or turbulence direct-
ly. Instead, it detects precipitation which may be associated with dangerous
thunderstorms and turbulence. The best radar reflectors are raindrops and
wet hail. The larger the raindrop, the better it reflects. Because large drops
in a small concentrated area are characteristic of a severe thunderstorm,
the radar displays the storm as a strong echo. Drop size is the most impor-
tant factor in high radar reflectivity. Generally, ice, dry snow and dry hail
have low reflective levels and often will not be displayed by the radar.
A cloud that contains only small raindrops, such a fog or drizzle, will not pro-
duce a measurable radar echo. But if the conditions should change and the
cloud begins to produce rain, it will be displayed on radar.
Figure 5.4-1. Reflective Levels
14 RDR-1600 Pilot's Guide

5.5 WEATHER DISPLAY CALIBRATION

The MFD Radar display should be calibrated to show four levels of target
intensity: Black (level 0), Green (level one), Yellow (level two) and Red
(level three). The meaning of these levels is shown in the following chart as
is their approximate relationship to the Video Integrated Processor (VIP)
intensity levels used by the National Weather Service (NWS). These levels
are valid only when (1) the Wx or WxA modes are selected; (2) the dis-
played returns are within the STC range of the radar (approximately 40
miles); (3) the returns are beam filling; and (4) there are no intervening
radar returns.
Display
Level
3
(Red)
2
(Yellow)
1
(Green
0
(Black)
TM106101(8/01) TM106101(8/01)
Table 5.5-1. Radar Display and Thunderstorm Levels
versus Rainfall Rates
Video Integrated Processor (VIP)
Categorizations
Rainfall Rate
Story VIP
mm/Hr. In./Hr Category Level
12 0.5 Strong 3
4-12 0.17-0.5 Moderate 2
1-4 0.04-0.17 Weak 1
Less Less than
than 1 0.04
RDR-1600 Pilot's Guide
Theory of Operation (Cont.)
Remarks
Rainfall Rate
mm/Hr. In./Hr.
Greater Greater Severe turbulence,
than 12 than 0.5 possible lightning
Light to moderate
turbulence is
2.5-12 0.1-0.5
possible with
lightning
Light to moderate
turbulence is
0.25-2.5 .01-0.1
possible with
lightning
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