USER'S GUIDE____________________________________________________________________
50 __________________________________________________________________ M210482EN-D
0911-075
Figure 18 Basic Operation of CL31 Sky Condition Algorithm in a
2D Time-Height Domain
The sky condition algorithm reports the total sky cover in octas with
values between 0 and 9. (One octa equals one eighth.) Value 9 is reported
only in a vertical visibility condition. In addition, the sky cover can have
values of -1 and 99. The -1 is reported if the data is missing or the
ceilometer is in stand-by mode. The value 99 is reported after the start-up
of the ceilometer indicating there is not enough data for algorithm
processing.
Table 7 Sky Cover Values from the Sky Condition Algorithm
Volume Sky cover
0–8 Cloudiness in octas
9 Vertical Visibility (VV)
-1 Data missing or ceilometer in stand-by
99 Not enough data
Vertical Visibility (VV) hits are considered as cloud hits if they are
above 2 000 meters. The cloud height is defined as (VV + signal range)
/2. Lower VV hits are assigned to a VV register during the last 10 minute
period. If the percentage of VV hits in the register exceeds 50 %, the sky
condition algorithm reports VV. The VV height is the average height of
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