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Operating Manual CHM 8k
R1.7 / 01-2020
Data Evaluation / Sky Condition Algorithm (SCA) 60
9.9 Mixing layer height
Aerosols which are detected near the ground spread in the lower air layer, where the upper limit can be
defined as a planetary boundary layer (onshore) and maritime boundary layer (offshore). The lowest
aerosol layer that can be identified within the boundary layer can interpreted as mixing layer height (MXL).
The MXL like all aerosol layer structures in the boundary layer depends on atmospheric conditions and
on sunny days mostly on daytime.
Aerosol layer heights can be identified by analyzing gradient signatures in the backscatter signal. The
quality of the detected aerosol layers depends very much on the local conditions and time. Table 20
shows an index describing the quality of the identified aerosol layers in terms of high accuracy and low
uncertainty.
Q-Index Description
/ (telegram)
-1 (NetCDF) There is insufficient raw data for a calculation
- (telegram)
-2 /NetCDF) Hardware error or system is not ready to measure
(telegram)
-3 (NetCDF) Algorithm cannot detect values
0 No particle layer detected
(index was not calculated in older firmware versions)
1 Particle layer detected with high accuracy (< 50 m)
9 Particle layer detected, but with low accuracy
Table 20 Q-Index description of aerosol layer height.
9.10 Cloud cover (BCC / TCC)
The cloud coverage is determined statistically from the behavior of the lower cloud bases over time. Here,
a distinction is made between the coverage of the lowest cloud layer (BCC: base cloud cover) and the
total of all cloud layers (TCC: total cloud cover). The values for these parameters are also stored in the
NetCDF files.
The time interval considered is height-dependent (Figure 28). The frequency of the occurring cloud layers
is determined for each height interval. This histogram is smoothed with a height-dependent weighting
function. Within this smoothed frequency distribution, the peaks are separated. All cloud bases within a
peak are bundled into a cloud layer.
Sections that contain cloud bases are counted against the total number of cone sections. The cloud cover
values are expressed as a percentage from this comparison. The final degree of coverage is reported in
eighths Table 21 lists the WMO code 2700 for the cloud cover index.
Eighth Description
- (telegram)
-2 (NetCDF) System hardware error or system not yet ready for operation
/ (telegram)
-1 (NetCDF)
-3 (NetCDF) Cloud bases could not be determined due to fog or other non-meteorological
reasons, or no observation was made
0 Clear sky
1 1 okta: 1/10
– 2/10
2 2 okta: 2/10
– 3/10
3 3 okta: 4/10
4 4 okta: 5/10
5 5 okta: 6/10