Transcript Folie 1 - unibe.ch

Institut für Meteorologie und Klimaforschung, Bereich Atmosphärische
Umweltforschung (IMK-IFU), Garmisch-Partenkirchen
Institut für Meteorologie und Klimaforschung, Bereich Atmosphärische
Umweltforschung (IMK-IFU), Garmisch-Partenkirchen
Sounding of Free-tropospheric Water Vapour with the Zugspitze DIAL
Thomas Trickl, Hannes Vogelmann
Topics:
1.Lidar at IMK-IFU
2.System Description
3. Measurements
4.Upgrading and future validation campaigns
NDACC sites in the GarmischPartenkirchen area
Lidar at IMK-IFU:
NDSC Lidar (since 1973)
water-vapour lidar (July 2004)
3 aerosol lidars
2 ozone lidars
The longest lidar measurement series (1973-2006)!
Sonde data: M. Furger, N. Ritter, PSI (CH)
Lidar Measurements of the Atmospheric Water Vapour
Raman lidar is usually preferred due to its capabilty of automatic operation.
With a high-power DIAL a similar performance may be achieved if the laser pulse energy
and the size of the receiver are made comparably large.
DIAL is substantially better during daytime; a range up to the tropopause may be achieved
also during daytime
For measurements covering the entire free troposphere a high-altitude site is advantageous
Routine measurements with a DIAL in the stratosphere require a base altitude of 7500 m
(935-nm absorption band)
So far achieved:
Routine measurements up to about 12 km; reliable system performance
Some improvements needed (laser, detector noise)
Operating Range of DIAL Measurements
Zugspitze (2962 m)
FTIR
Lidar (2674 m)
Schneefernerhaus
Advantages of the High-altitude Site:
– Mostly outside the moist atmospheric boundary layer
– outside the fog layer in autumn and winter
– earlier beginning of measurements also in summer
Flow box: Temperature stability 0.5º
Durch Minimum an
The Move: April 10-12, 2003
–24º C at the summit!!!!
Modified High-voltage Unit of Ti:Sapphire Laser
Oil bath
Influence of the Line Shapes
For a narrow-band laser not
only the shape of the molecular
absorption line as a function of
the altitude needs to be taken
into account:
The backscattered light has a
complex shape also depending
on the altitude.
Forecast ETH Zürich
Daytime measurement under very dry
conditions
Validation by intercomparison by radiosondes
lauched at Garmisch-Partenkirchen (LMU)
2007: First Annual Series
HP
TP
2007: First Annual Series
Cirrus
2007: First Annual Series
RH = 1%!!
Conclusions
1. The lidar performs reliably and rather stable; measurements can be started
within 1 h after the arrival at the laboratory. With an improved control of the
cavity end mirrors even an automatic operation over many hours should be
possible.
2. The noise-limited sensitivity above 10 km is about 1.51020 m–3 or 18 ppm.
The theoretical limit is 1-2 ppm and can almost be reached with the specifications expected after the next upgrading.
3. The laser has been operated with just roughly 100 mJ in order to avoid optical
damages; an upgrading to more than 400 mJ will be attempted in 2008; 700
mJ require major changes in the laser power supply to eliminate arcing.
4. The preamplifiers of the APDs produce too much noise (currently almost 10–3
of the peak signal). This woud improve after the laser upgrading; however, a
new very sensitive near-IR PMT has become available and is expected to
reduce the noise-to-peak-signal ratio to <10–5.
5. A thorough system validation is planned following the upgrading in cooperation with DLR.
Thank you!