Campbell SkyVUE 8, Product Manual

Page: 105 / 116

Appendix A. Measurement of
the attenuated backscatter
profile
A.1 Initial measurement 93
A.2 Backscatter onset height detection 93
A.3 Produce attenuated backscatter output message 94
A.1 Initial measurement
l
Pulse the laser and measure the backscatter at optimal gains.
l
Derive the impulse response and impulse correct the backscatter signal using the inverse
filter derived.
l
Remove the residual offset and slope from the impulse corrected backscatter.
l
Apply an overlap correction based on the known generic overlap function of the SkyVUE 8.
l
Apply the backscatter calibration constants.
l
Remove the laser and electronic artefact signature. This is specific to the individual SkyVUE
8 and determined during calibration.
A.2 Backscatter onset height detection
l
Filter the backscatter with 20 m (65.6 ft) and 300 m (984 ft) width filters.
l
Look for a 1500 m (4921 ft) block width where the standard deviation is at a minimum for
both the 20 m (65.6 ft) and 300 m (984 ft) width filtered backscatters.
l
Create a detection threshold by multiplying the 20 m (65.6 ft) and 300 m (984 ft) standard
deviations by a constant.
l
Find the onset of backscatter height by working from the highest height bin downwards
until the backscatter is above one or both of the two detection thresholds.
SkyVUE™8 (CS136) LIDAR Ceilometer 93