Lufft CHM 15k Nimbus, Manual

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Data Evaluation/ Sky Condition Algorithm (SCA)
70 Revision R09, November 2016
9.11 Cloud amount/ cloud cover (BCC / TCC)
The cloud coverage value is calculated from the cloud bases and their time
course. The base cloud cover (BCC) from the lowest cloud base and the total
cloud cover (TCC) are written in NetCDF files.
The considered time interval depends on the altitude, see Figure 27. For each
altitude interval the frequency of cloud bases are calculated. This histogram will
be smoothed using a height depending weight function. Within the smoothed
frequency distribution, peaks will be separated. All cloud bases in the space of a
peak will be clustered to one cloud layer.
The calculation of the total cloud cover value and the separated cloud layers are
done within a rectangle depending on time and altitude. For this purpose the
selected time interval (truncated cone) will be divided in a fixed number of small
truncated cones. Parts containing cloud bases are counted against the total
number of cone parts. The cloud cover values is expressed as a percentage value
from these comparison. Finally the percentage value is expressed in oktas.
Table 19 lists the WMO code for the cloud cover index.
1 layer can be detected, but with a high uncertainty and low
accuracy
9 layer can be detected with a high accuracy (less than 50 m)
oktas description
- (telegram)
-2 (NetCDF) system hardware failure or system not ready
/ (telegram)
-1 (NetCDF)
-3 (NetCDF) cloud is indiscernible for reasons other than fog or other
meteorological phenomena, or observation is not made
0 clear sky
1 1 okta : 1/10 - 2/10
2 2 oktas : 2/10 - 3/10
3 3 oktas : 4/10
4 4 oktas : 5/10
5 5 oktas : 6/10
6 6 oktas : 7/10 - 8/10
7 7 oktas or more, but not 8 oktas : 9/10 or more, but not 10/10
8 8 oktas : 10/10
9 9 - sky obscured by fog or other meteorological phenomena
Table 19: Cloud amount / cloud cover values related to WMO code 2700.
Q-Index description
Table 18: Quality Index description, of the aerosol layer height