the cloud base is just the beginning: advanced
TRANSCRIPT
The cloud base is just the beginning: Advanced applications of Vaisala ceilometersChristoph Münkel, Vaisala GmbH, Hamburg, Germany
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Contents� Introduction to Vaisala ceilometers
�Ceilometer calibration
�Monitoring particle emissions
�Elevated dust layers
�Extinction profiles
�Mixing layer height determination
�High resolution profiling
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Single lens ceilometer Vaisala CL31
� Simple and reliable instrument design.� Sufficient overlap already 10 m above the system. � More than 4000 units in operation.
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Single lens ceilometer Vaisala CL51
Lev-Yatir, Israel Wien Hohe Warte, Austria Station Nord, Greenlandoperated by KIT/IMK-IFU operated by ZAMG operated by DTU Wind Energy, Roskilde
� Unchanged optical setup compared to CL31.� Larger lens and modified electronics increase SNR significantly.� Qualified instrument for boundary layer investigation.� Designed for harsh environments.
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16384 laser pulses are accumulatedwithin 2 s for a single reported profile
No problem forthe cloud base
detectionalgorithm
Speed of light: 300*106 m/s = 300 m/µs
There and back:2*1500 m in 10 µs
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A typical CL51 backscatter profile density plot
Cloud
Nocturnal layer Precipitation
Melting layer
Residual layer
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Hot topic in the scientific community –calibration of ceilometers
�WG 1 of TOPROF is investigating the following methods:
�Vaisala ceilometers are factory calibrated. �During operation the calibration factor is maintained by
monitoring laser power and window transmission.
–Rayleigh Calibration
–Cloud calibration
–Reference Lidar (not operational)
TOPROF (COST Action ES1303)
Towards operational ground based profiling with ceilometers, dopplerlidars and microwave radiometers for improving weather forecasts
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Are results from different ceilometerscomparable ? A random investigation offour co -located CL31 ceilometers�Before purchasing 1000 CL31 ceilometers, the US National
Weather Service did extensive testing.�For more than two years, up to five co-located ceilometers
were operated in a circle with a diameter of 30 m.�The following slides show 25 minutes with a rather stable
3700 m cloud base.�Signal integral over the whole measuring range should not
differ significantly.�On the randomnly chosen time 2008-07-02 00:54:00, the
average signal integral of the four units was 0.0152 sr-1 witha standard deviation of 0.00059 sr-1 corresponding to 3.9 %.
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Some thoughts about Rayleigh calibration
�Rayleigh calibration method requires ceilometer data from a very clear night, averaged over several hours.
� It tries to identify regions within the attenuated backscatterprofile that are practically aerosol free.
�But how can we be sure that we chose the right region?�The following examples show that there is very often
something up there that a ceilometer has difficulties to see.�Consequently Vaisala favours the cloud calibration method
introduced by Ewan O‘Connor.http://www.met.reading.ac.uk/~swr99ejo/publications/lidar_calibration.pdf
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HSRL at Hyytiälä – a powerful lidarreveals a lot of elevated aerosol layers
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CL51 at Hyytiälä – HSRL structures arebarely visible
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HSRL at Hyytiälä – a powerful lidarreveals a lot of elevated aerosol layers
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CL51 at Hyytiälä – HSRL structures arebarely visible
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Monitoring particle emissions
A classical lidarapplication: Backscatter
signal peaks hint on increased particle
concentration
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Monitoring particle emissions
A classical lidarapplication: Backscatter
signal peaks hint on increased particle
concentration
Ceilometers register ice crystals aloft. Monitoring
these events helps to understand the process of arctic cloud formation.
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Elevated dust and ash layers
Dust layer from Gobi Desert
Mongolia
Beijing
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Extinction profiles
�Ceilometers report the attenuated backscatter part of thesimplified lidar equation.
�According to ISO 28902-1 (ground-based remote sensing ofvisual range by lidar), profiles of the extinction coefficient α canbe derived from this if
� α ≥ 0.0015 m-1 (corresponding to MOR ≤ 2000 m), � a linear and range-independent relation of α and β is assumed.
�These assumptions are fulfilled to a high extent during hazeevents in megacities.
44 344 214434421rbackscatte attenuated
2
specific instrument
02),(),()(
2),( λτλβηλ xxtxOAP
x
cxP ∆=
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A haze event in Beijing – attenuated backscatter
Cleaning the window increases
attenuated backscatter
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A haze event in Beijing – extinctionprofiles increase information content
Cleaning the window does not affect extinction
Attenuated backscatter too
low for application of Klett-Fernald
algorithm
Formation of a dense haze layer
only visible in extinction profiles
MOR600 m
1000 m
1500 m
2000 m
3000 m
5000 m
10000 m
15000 m
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Ground extinction coefficientverification with MOR
�There are various CL51 installations with attached visibilitymeter reporting MOR (meteorological optical range).
�These values could be used to verify the validity of theassumptions made for the derivation of extinction profiles.
CL51 andVaisala FS11 on research vessel
Polarstern
CL51 andVaisala PWD52
at Wien Hohe Warte
CL51 andVaisala PWD52
on FINO3 platform
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Extinction coefficient verification withforward scatter visibility meter PWD52
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Mixing layer height determination
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Negative gradient plot
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Pick gradient minima as layer tops
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BL-VIEW algorithm reports up to 3 layers
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BL-VIEW algorithm reports up to 3 layers
Presentation with the Vaisala SW product BL-VIEW
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Radiosondes confirm layer tops
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High res plot shows the good near-range behavior
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A CL51 with BL-VIEW is running in theFinnish Embassy in Beijing
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Two co -located CL51 ceilometers at Hamburg Wettermast
High res
modeCL51
Standard modeCL51
Standard mode
High res mode
PRF 8.192 kHz 8.192 kHz
Range resolution
10 m 10 m
Measuring range
7700 m 1800 m
Profile report interval
16 s 0.5 s
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Investigation of rising and falling aerosol plumes with high res mode
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This cooled bubble falls 120 m in 60 s
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� Many thanks to these institutions and individuals that helpedproviding data and photographs for this presentation
� Sven-Erik Gryning, Rogier Floors
� Martin Piringer, Christoph Lotteraner, Erwin Petz
� Fabian Eder, Matthias Mauder
Acknowledgements
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CL31 CL51
Minimum range resolution 5 m 10 m
Typical range resolution for boundary layer scans 10 m 10 m
Minimum report interval 2 s 6 s
Typical report interval for boundary layer scans 16 s 36 s
Measuring range for cloud base detection
0 … 7500 m
0 … 13000 m
Backscatter profile range 0 … 7700 m 0 … 15400 m
Range for boundary layer fine structure profiling 0 … 4000 m 0 … 4000 m
Total height 1190 mm 1531 mm
Total weight 31 kg 46 kg
Weight of measurement unit 12 kg 18.6 kg
Laser type InGaAs diode InGaAs diode
Laser wavelength 910 nm 910 nm
Eye-safety class 1M 1M
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Ash from the Puyehue -cordon -caulleeruption monitored over Antarctica
Cloud
Volcanic ash cloud
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NOAA HYSPLIT backward trajectories confirm volcanic ash cloud detection
Puyehue-cordon-caulle
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Arctic ice crystals aloft
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Arctic ice crystals aloft