CL31_Operator_Training

z
dz’
is the two-way atmospheric transmittance (equals to 1 in a clear weather)
e
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Extinction coefficient relates to visibility
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Designed for harsh weather
Shield • shield with a blower / heater enable reliable operation in precipitation and in extreme temperatures Tilting • tilting for further protection for precipitation and avoidance of specular reflection from ice crystals • automatic tilt angle measurement and correction Easy access door • fast service access even in rain Reliable solar protection • optical filters instead of mechanical shutters
-2 ∫ σ(z’) 0
z
is the instantaneous power received from distance z (Watts - W). is the effective pulse energy (taking all optics attenuation into account) (Joules = J, 1J = 1 Watt - second). is the speed of light (meters per second - m/s). is the receiver aperture (m2). is the distance in question (m). is the volume backscatter coefficient at z (m-1srad-1).
Vaisala Ceilometer CL31
Operwenku.baidu.comtor Training
Contents
Introduction
CL31 key features LIDAR operating principle Single lens optics Cloud determination logic
Modular design • easy troubleshooting and fast service • modules easily replaced in field • no re-alignment of optics needed with Tx or Rx replacement
Automatic fault analysis for low down time • in case of a fault the suspected module is indicated in the status message and also locally with a LED • status information also available through data line for remote trouble shooting
Data message types Line connections
Commands
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Vaisala Ceilometer CL31 - main features
• 0...25,000 ft (0...7500 m) range • Enhanced single lens optics • excellent accuracy for the whole range • high performance in all weather • DSP based fast electronics • 2 second measurement cycle • Extensive self monitoring functions • reliable automatic operation • Automatic trouble shooting aids • high data availability • Eye safe diode laser lidar
REFLECTED LIGHT
10 m / 33 ft TOTAL TRAVEL OF LIGHT 66 ft 0 ft
SAMPLE at 67 ns
SAMPLE 0 ns
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Laser beam width
Height 7.5 km (25 000 ft) Width 8 meters
Maintenance and service HANDS-ON exercises
Commands and communication Maintenance Troubleshooting and repair
Installation Hardware units Communication
• Short (100 ns) pulse of light is transmitted into air • Receiver monitors the light backscattered by aerosols • Altitude of backscatterer is given by time (speed of light is 30 cm/ns ~ 1 ft/ns) • Several profiles are summed to increase signal to noise ratio
Receiver Mirror Lens
Transmitter
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Optical signal comparison - light rain and low cloud Ceilometer Optical Signals in Light Rain (same normalization)
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Vaisala Ceilometer CL31
High performance and data availability
Based on powerful Digital Signal Processor • fast, 2 second measurement cycle • 10 kHz pulse frequency • sophisticated algorithms • high resolution backscatter profile reporting
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Enhanced single lens optics
• Lens divided into transmitting and receiving areas • middle of the lens focuses the outgoing laser beam and outer part collimates backscattered light onto the receiver • Division made by an inclined mirror with a hole • No complicated cross talk compensation techniques needed • Coaxiality of transmitted beam and receiver field of view provides robustness against changes in mechanical alignment
3. 8 km (12 500 ft)
4 meters
0 m (0 ft)
70 mm
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Benefits of single lens optics
• Strong and stable signal even from the safety critical low altitudes => measurement range starts virtually at 0 altitude • Good overlap of laser beam and receiver field of view decreases effect of multiple scattering, leading to more consistent operation during precipitation and fog • More robust against changes in mechanical alignment • Compact mechanical design
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Extensive self-monitoring
Self-monitoring for reliable operation • laser power, receiver sensitivity, internal voltages, window contamination, internal temperatures, optical alignment
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CL31 Biaxial ceilometer
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Optical Signal (a.u.)
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Height (m)
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Optical signal comparison - fog
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LIDAR operating principle
LIDAR = LIght Detection And Ranging
Top Level 7.5 km / 25,000ft TOTAL TRAVEL OF LIGHT 50,000ft 7.49 km / 24,967 ft SAMPLE at 49,93 μs SAMPLE at 50 μs Last in the scan
200
Height (m)
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LIDAR equation for return signal strength
c A -2 ∫ σ(z’) dz’ Pr( z ) = Eo β (z) e 0 2 2 z
Pr(z) Eo c A z ß(z)
Ceilometer Optical Signals in Fog (normalized at 660 m)
200 180
CL31 Biaxial ceilometer
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Optical Signal (a.u.)
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