Campbell SkyVUE 8, Product Manual

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2.1 Introduction
The SkyVUE 8 is a LIDAR (LIght Detection And Ranging) that emits short pulses of near infrared
light into the atmosphere from a semiconductor laser. The pulses of infrared light are scattered
back by aerosols including cloud droplets. The time between transmission of the pulse and the
return signal gives the range, and therefore height, of the scattering aerosols. The variation in the
strength of the back-scattered light signal with height gives a profile of scatter coefficients and
allows identification of cloud bases. If significant scattering is detected without a defined cloud
base, then a vertical visibility can be calculated.
The control system of the SkyVUE 8 is divided into three modules, DSP, TOP and PSU as follows:
DSP (Digital Signal Processor) is the main data processing and communications unit of the
SkyVUE 8. It hosts two separate time keeping circuits that are cross checked. An alarm is triggered
if the circuits disagree.
TOP (top of the unit) provides safety shutdown features such as over and under laser output
level. It also contains the calibration circuitry and dirty windows system.
PSU (Power Supply Unit) controls the power supply including battery charging and deep
discharge protection.
The SkyVUE 8 has a rugged environmental enclosure that protects the instrument from the
harshest conditions and will measure the atmosphere with high stability and repeatability.
2.1.1 Cloud height detection
A scatter profile is measured as described in Measurement of the attenuated backscatter profile
(p. 93).
Cloud height detection is carried out as described in Cloud height calculation (p. 95). Up to four
cloud heights can be detected.
If clouds are not detected, the SkyVUE 8 will give one of these reports:
l
No significant backscatter.
l
Full obscuration determined but no cloud base detected. This is reported if the criteria for
detecting cloud base is not met but the integrated scattering coefficient reaches the limit
of vertical visibility below a set height limit. The default value is 2000 m (6560 ft) but can be
changed by the user. The height at which this occurs is given as vertical visibility.
l
Some obscuration detected but determined to be transparent is reported if scattering is
detected but no cloud is detected and the calculated vertical visibility exceeds a set height
limit.
SkyVUE™8 (CS136) LIDAR Ceilometer 6