Table of Contents
Ceilometer CT25K
Mentor: J.H. Schween
Principle
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.
Instrument
Current setup at Research Center Jülich on the roof of IEK-8.
Data
- If you are interested in receiving data please contact the instrument mentor: J.H. Schween
<html> <a href=“http://atmos.meteo.uni-koeln.de/~hatpro/jue/ceilo/current/index.html” target=“_blank”> <img src=“http://atmos.meteo.uni-koeln.de/~hatpro/jue/ceilo/current/bscat.png” width=420> </a> click to enlarge </html>
History
Specifications
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 |