Icing; Snow; Lightning And Static Discharges; Range Resolution - Telephonics RDR-1600 Pilot's Manual

Weather Operations (Cont.)

6.5.4 Icing

There is reason to believe that the radar will be of assistance in locating
areas of heavy icing conditions. However, weather radar has not yet proved
its ability to distinguish between super-cooled water droplets and ice crys-
tals, since both are usually quite small. Needless to say, the operational
problem in each case would be different. In the first case icing would defi-
nitely exist but in the second case the pure crystals would offer no danger.
1. It should be remembered, however, that super-cooled water and ice
crystals can co-exist. In each case the radar echo would be small or
even nil due to the minute size of the free water particles. At this time, it
appears fairly certain that radar is not going to give warning of cloud icing
unless it happens to be involved with active precipitation at the time.
When precipitation is occurring, however, the areas of maximum ice
exposure should appear as sandy or grainy echoes.
2. An icing condition that the radar might possibly detect is the intermittent
moderate or heavy icing condition associated with unstable air lifted by
frontal action or orographic effects. In this situation, the cumulus cells
are hidden by surrounding cloud layers but could be spotted by radar.
This would be of assistance in avoiding the moderate-to-heavy icing
which occasionally occurs in cumulus clouds.
WARNING
Thunderstorm icing can be extremely hazardous.

6.5.5 Snow

Dry snowfall has not been detected with any success on weather radar.
However, a characteristic sandy or grainy echo identifies the presence of
steady moderate-to-heavy wet snow. Such echoes are not readily obvious
and require a little study of the display before they can be seen.

6.5.6 Lightning and Static Discharges

Lightning and static discharges could scatter the display momentarily.
However, the general presentation is unaffected and should return to
normal within 1 scan.
24 RDR-1600 Pilot's Guide

6.5.7 Range Resolution

The ability of the radar system to resolve closely spaced targets in range
depends on transmitter pulse width. In long range modes, the RDR-1600
can distinguish objects spaced as close as 0.19 nm (385 yds.) apart. In
Search 1 (SR1) and Search 2 (SR2) modes on ranges of 20 miles and
below, the resolution is improved to 0.04 nm (80 yds.).

6.5.8 Azimuth Resolution

The ability of the radar to resolve adjacent targets in azimuth depends on
antenna beam width and range to the target. The diameter of the radiated
beam increases as it gets further from the antenna. Larger antennas have
narrower beam widths and, therefore, produce better ground mapping and
weather pictures.
Targets separated by a distance less than the beam diameter will merge
and appear on the indicator as one.
TM106101(8/01) TM106101(8/01)
Weather Operations (Cont.)
Figure 6.5.8-1. Azimuth Resolution
RDR-1600 Pilot's Guide 25