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Ceilometer CT25K

Mentor: J.H. Schween


A ceilometer measures the cloud base height, called ceiling in aviation. It is based on the light detecting and ranging (LIDAR) principle, i.e. it sends laser pulses and measures the backscattered light. From travel time the distance of the back scattering object can be determined. From strength and attenuation of the backscattered signal the backscatter coefficient is determined. The instrument identifies cloud bases by caluclating visibility from the backscatter coefficient and identifying the height from which on you cant see the ground any more. If the lower clouds are transparent it can detect up to three distinct cloud layers. In clud free cases we can use the backscatter profile for an estimate of boundary layer height.


Current setup at Research Center Jülich on the roof of IEK-8.


  • If you are interested in receiving data please contact the instrument mentor: J.H. Schween

Current data:

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Period Place Project
11/10/2010 - today Research Center Jülich, Germany
09/2007 - 05/10/2010 Selhausen, Germany TR32
winter months 2008/2009 UFS, Zugspitze, Germany TOSCA
2006 - 2007 Nangatchori, Benin AMMA


See manual section 1.2.6 page 8 and section 5.2.2 page 56.

Parameter Specification
Wavelength 905 nm
Pulse Power 16 W typical
Pulse energy 1.6μJ ±20%1)
Average Power 8.9 mW
Pulse Width 100 ns
Pulse Repetition Rate (PRR): 5.57 kHz
Number of pulses (PQTY): 65,5362)
Averaging time: 11.7sec (=PQTY/PRR)
Time resolution 15sec 3)
Range resolution 50ft = 30m (see here)
Range 200…25,000 ft. (60…7500 m)
Laser Divergence ± 0.53×0.75 mrad (edge×diagonal4))
Field-of-View Divergence ± 0.66 mrad
Telescope diameter 145mm
Tilting angle 2.5° as of Aug 21 2015 (7° before…)
Size 760 x 280 x 245 mm
Power Consumption 365 W
Weight 40 kg
Manufacturer Vaisala
factory adjustment
65,536=2^16=64*1024=4^(7+1) the 7 contained in the last is what you find in the status message
⇒ 3.3sec for processing and data transmission
the laser is a diode with square shape. The beam thus a pyramid with different opening angles for neighbouring and opposite edges
instruments/ceilo/ceilometer.txt · Last modified: 2022/12/19 17:17 by jan