Lufft CHM 15k, Руководство пользователя

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Operating Manual CHM 15k R13 / 07-2019
Data Evaluation / Sky Condition Algorithm (SCA) 58
Figure 28 Evaluation process for different cloud parameters.
9.5 Parameters for data evaluation
A set of parameters control the data evaluation routine. System dependent data are stored on the laser
optical module (LOM). Data accessible to users are listed in Table 4 and Table 5.
If the instrument is tilted to the zenith and the zenith angle is entered correctly, the cloud distance and
other ranges are corrected by this angle.
9.6 Determination of the maximum detection range (MXD)
The maximum detection range corresponds to the maximum distance from which significant signals are
still being measured. It results from the signal / noise ratio (S/N) as a function of the distance. At altitudes
outside the boundary layer, only clouds or denser aerosol layers generate significant signals. The
maximum detection range is calculated independently of the cloud detection algorithm and can be used
to check the result, e. g. if the ceilometer can detect neither a cloud layer nor a vertical optical range.
Here, the MXD can be used to check whether the result "Clear sky" is correct.
9.7 Vertical optical visibility (VOR)
The method for determining the vertical visibility (VOR: Vertical Optical Range) is described in ISO
standard 28902-1:2012. The step by step approach to how we use VOR is described below:
First, all sections in the backscatter signal (9.2 Preparation of the measured data) with a signal / noise
ratio > 5 are identified. For these relevant intervals, the Klett inversion method is used to process the
extinction
α(r).
The vertical optical visibility is the distance, where the integral of the extinction is equal to 3.
∫ 𝑎(𝑟)𝑑𝑟
𝑉𝑂𝑅
0
= 3
The range for calculating VOR is limited to an altitude of 3 km. The data output depends on the selected
data telegram. In the standard telegrams 1 - 3, the vertical visibility is always transmitted, while in the
user telegrams 8 and 9, which correspond to the CT25k data telegram, VOR or the lower cloud limit is
transmitted.