Ozone Lidar

Stationary Ozone Lidar

The stationary ozone lidar at IMK-IFU was built in 1990 and upgraded twice ever since [e.g., Eisele et al., 1999]. It features a particularly wide vertical range from 0.3 km above the ground (740 m a.s.l.) and typically 3 km above the tropopause, an accuracy of about 5 % at least up to the middle troposphere, as well as a high vertical resolution (30 to 500 m, depending on the altitude). The laser system is a narrow-band krypton fluoride laser (Lambda Physik, LPX250) emitting 450-mJ pulses at 248.5 nm with a repetition rate of 100/s. The operating wavelengths 277 nm, 292 nm and 313 nm are generated with conversion efficiencies between 20 % and 32 % by stimulated Raman shifting this radiation in hydrogen and deuterium cells (see figure below). The emissions at these wavelengths are differently absorbed by ozone, which yields information on different altitude ranges.

Laser laboratory of the stationary ozone lidar at IMK-IFU, showing the KrF laser (orange) and the two 2-m Raman cells.

Due to the eight-decade dynamical range of the lidar signal two Newton telescopes (with 0.13 and 0.5 m diameter, respectively) are used for a separate near- and far-field detection of the backscattered light. The light is spectrally decomposed in 1.1-m grating spectrographs with a resolution of about 0.3 nm. Both analogue and single-photon counting techniques are used for the data acquisition. Ozone profiles are retrieved by evaluating the differential absorption for the wavelength pairs 277 nm/313 nm, 292 nm/313 nm or 277 nm/292 nm. This results in at least five partially overlapping profiles that are intercompared for an internal quality control. The measurements are routinely compared with the results of the IFU summit stations Wank and Zugspitze, as well as occasionally with ozone profiles from the measurements at the Hohenpeißenberg observatory 38 km to the north.
 

Reference:

Eisele, H., Scheel, H. E., Sladkovic, R., and Trickl, T.: High-Resolution Lidar Measurements of Stratosphere-Troposphere Exchange, J. Atmos. Sci., 56, 319-330, 1999.