Ceilometer CT25K
CT25K-U059en-2.1 User’s Guide
85
The counts are summed starting from the lowest bin. The bins where the sum
exceeds 1/33, 3/8, 5/8 and 7/8 of the maximum value are recorded as layer
heights. The corresponding cloud amounts for these layers are 1,3,5 and 7
oktas. In addition, the minimum number of counts (hits) for each layer has to
be exceeded:
1st layer 17 (3.4 hits)
2nd layer 10 (2 hits)
3rd layer 25 (5 hits)
4th layer 25 (5 hits)
Table 5-5 Minimum number of counts (hits) for each layer
In case the minimum count is not exceeded in the assigned bin, the algorithm
seeks three bins upwards and then three bins downwards if one of these bins
has the required number of counts. However, if none of the bins contains
enough counts, the original bin is used as the layer height.
If the resulted layers are close to each other, it is reasonable to combine them
rather than define them as separate layers. If the distance between two cloud
layers is less than the minimum distance shown in Table 3-4, the layers are
combined. The height of the combined layer is that of the lower layer and the
cloud amount of the combined layer is that of the upper layer.
Layer height Minimum distance
< 1 000 ft 100 ft
1 000 ... 2 000 200 ft
2 000 ... 3 000 300 ft
3 000 ... 4 000 400 ft
4 000 ... 5 000 500 ft
5 000 ... 15 000 1 000 ft
15 000 ... 25 000 5 000 ft
Table 5-6 Minimum distance between different cloud layers
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