Caeli Water Vapour Raman Lidar Calibration At The Cabauw Experimental Site For Atmospheric Research

Water vapour is a crucial parameter in atmospheric physics. Concentrations are low at upper tropospheric al- titudes, but radiation effects are sensitive to water vapour abundance at these levels. Obtaining reliable data of low water vapour concentrations in the upper troposphere is challenging. The Raman lidar technique for water vapour can meet this challenge, however, the Raman lidar water vapour data rely on an external source for calibration. For the Raman lidar Caeli in Cabauw, operational radioson- des launched in De Bilt, about 22 km North-East of the lidar location are routinely used for this. Differences in space and time between the observations influence the consistency and quality of the calibration.
Various in-situ and remote observations of humidity are available at Cabauw that are better collocated and syn- chronised with the lidar measurements. These collocated observations could also be used for the lidar calibration as an alternative to the radio soundings. Among the pos- sibilities are GNSS and microwave radiometer and tower based in-situ humidity measurements. In this paper we explore the possibilities for applying those for the Raman lidar calibration in Cabauw.