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 Garmisch- Partenkirchen area

3 aerosol lidars 2 ozone lidars water-vapour lidar (July 2004) Lidar at IMK-IFU: NDSC Lidar (since 1973)

The longest lidar measurement series ( )!

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

Schneefernerhaus Zugspitze (2962 m) Lidar (2674 m) FTIR

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

Durch Minimum an Flow box: Temperature stability 0.5º

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  m –3 or  18 ppm. The theoretical limit is 1-2 ppm and can almost be reached with the specifica- tions 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 co- operation with DLR.

Thank you!