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PRIMUSr 880 Digital Weather Radar System
With the very short time between radar pulses when in the turbulence
mode (one pulse every .0008 second), little or no turbulence results in
little or no change in the size or position of the raindrops. This results
in little or no change in the individual returns from each raindrop and a
commensurate little or no change in the total return vector. Therefore,
when there is little or no difference between two subsequent total return
vectors in the same range bin, there is little or no turbulence in that
range bin. This is illustrated by comparing figures 5- 30 and 5- 31.
If turbulence is present in the precipitation, there is a significant change in
the raindrop size and/or position between the subsequent radar pulses.
This difference results in a change in the individual return vectors from
each raindrop and a commensurate change in the total return vector.
Therefore, if there is a significant difference between pairs of total return
vectors for the same range bin, that bin contains turbulence and is
displayed in white. This is illustrated by comparing figures 5- 30 and 5- 32.
The presence of turbulence is detected by comparing the amplitude of
subsequent total return vectors.
To measure raindrop motion, the turbulence detection circuitry measures
the raindrop motion directly toward and away from the antenna. Raindrop
motion that is perpendicular to the antenna does not produce any doppler
effect and cannot be measured by the turbulence detection circuitry. For
this reason, there can be areas of turbulence not detectable by radar, or
the displayed areas of turbulence can change from antenna scan to
antenna scan as the turbulence throws the raindrops in various directions.
WARNING
AREAS
OF
TURBULENCE
CAN
NOT
ALWAYS
BE
DETECTED BY THE RADAR.
A28- 1146- 102- 00
Radar Facts
5-43
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