Campbell SkyVUE 8, Product Manual

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Appendix C. Sky condition
algorithm description
The SkyVUE 8 sky condition algorithm follows guidance from ICAO and WMO documents
1
and is
based on 30 minutes of data. For this reason, sky condition is not available for 30 minutes after
power cycling the sensor, a reboot, or changing measurement parameters. The sky condition
algorithm is as follows:
Each measured hit comprising the lowest cloud height, (vertical visi onset of backscatter) /
2 and a weighting of 1 or 2 is stored in a running half hour buffer.
The weighting is 2 for hits in the last 10 minutes and 1 for hits in the previous 20 minutes.
If >50% of the hits in the latest 10 minutes are vertical visibility, then the vertical visibility
averaged over the last 10 minutes is reported. Only hits below the vertical visibility height limit set
are used.
The buffer is sorted in height order and hits combined into bins with the following widths:
Height Bin width
0 – 5000 ft
(0 – 1524 m)
100 ft
(30.5 m)
5000 – 15,000 ft
(1524 – 4572 m)
200 ft
(61 m)
15,000 – 26,250 ft
(4572 – 8000 m)
500 ft
(152 m)
For each bin a mean height is calculated by the following:
Hi = ∑(h
i
w
i
)/∑(wi)
Where w
i
is the weight (1 or 2) of the hit with height h
i
Bins are then reduced. A distance (D) between adjacent bins is calculated by the following
equation:
D = N
i
N
j
(H
i
-H
j
)2/N
i
+N
j
1
ICAO 9837 Manual on Automatic Meteorological Observing Systems at Aerodromes.
WMO – No. 306 Manual on Codes
SkyVUE™8 (CS136) LIDAR Ceilometer 96