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At the German Arctic station (Koldewey station, 78.9 degree(s)N, 1.9 degree(s)E) in Ny- Alesund we are operating a combined Ozone & Aerosol LIDAR which is capable to measure stratospheric profiles in the UV at 308 nm and 353 nm and in the visible at 532 nm at night as well as during daytime. In order to extend our measurements further down into the troposphere we developed a new detector unit. In our experimental set-up used up to now the backscattered light from lower altitudes was completely blocked by means of a mechanical chopper to avoid saturation of the photomultipliers. A new design of the chopper will block the signal differentially which permits the receiving of a well-defined part of the signal. In this way we can obtain ozone profiles down to altitudes of about 5 km. In comparison to other tropospheric LIDARS, which require two acquisition systems for different altitude ranges, our design has the advantage that the better resolution of photon counting can be used for the whole range from 5 to 40 km altitude. The new detector unit has a completely new optical set- up. The alteration between night- and daytime configurations have been simplified and respective Raman-shifted signals by atmospheric N2: 332, 385, and 607 nm have been added. These latter signals allow an aerosol correction to the ozone signal which is presently necessary due to the strong input of the volcanic aerosol in the stratosphere originating from the Mount Pinatubo eruption in 1991 and the generally higher aerosol content of the troposphere.
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