Between April and September 2009 a Vaisala and a Jenoptic Ceilometer were running in Selhausen and Jülich ~2km apart from each other.

The instrument in Selhausen changed two times:

• till April 30 7 UTC it was a Vaisala CT25K borrowed from the Met.Inst.of Univ. Bonn.
• From April 30. 08UTC till June 5, 07UTC it was a Vaisala CL31 borrowed from the manufacturer in replacement for our instrument which needed repair.
• From June 5, 08UTC data come from our own Vaisala CT25K.

The Instrument in Jülich was a Jenoptic CHM15K borrowed via the Met.Inst.Bonn from the german weather service (DWD). The Gap from end of April till Mid of August is due to problems with the very basic raw data acquisition system we used.