Ceilometer
Ceilometer CHM15k determines up to three layers the cloud base and penetration. In addition, the temporal variability of these parameters and a vertical perspective were determined.
All this data were determinded from the uncalibrated signal of a vertically aligned lidar. The spatial resolution amounts to 15 m, the time can be selected freely, normally we use 1 minute.
The ceilometer determines the cloud base edges in a frequency range close to the visible one, so that it achieves the same result as it would have a human observer. The cross-section of backscattered cloud droplets are proportional to their surface. In contrast, the backscatter cross-section at the frequencies of (cloud-)radars is proportional to the diameter d6. Therefore a few large droplets suffice to feign a lower cloud base to the radar.
The graph below shows a day´s measurement, which was executed in Massada, near to the dead sea in isreal. The coloured code corresponds the 10-times of 10th-logarithm of backscattered energie. White points show the cloud base edges.
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Fig. 1: Ceilometer during transport | Fig. 2: Measurement of Ceilometer |
Technische Parameter: |
Range: | 30 m to 15000 m (realistic minimum level rather at 150 m or 300 m) |
Spatial resolution: | 15 m |
Test time: | 5 s to 60 min, mostly 60 s |
Measure: | Backscatter, deduced: Cloud heights up to 3 layers, penetration/cloud thickness, vertical visibility |
Measurement principle: | Lidar |
Wavelenght: | 1064 nm |
Spread: | 0,1 nm |
Pulse lenght: | ca 1 ns |
Pulse rate: | 5-7 kHz |
Beam diameter, widened: | 90 mm |
Laser divergency: | 100 μrad |
Energy per pulse: | 8 μJ |
Maximal power consumption: | 0,8 kW |