Comparison of Cloud Classification methods

Cloud properties play an important role in the evaluation and interpretation of Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements. Clouds strongly influence the length of atmospheric light paths, and are thus important for deriving the aerosol optical depth (AOD) and vertical column density (VCD) of trace gases from MAX-DOAS measurements. As such, information about the cloud properties is important to interpret the data.
This study focuses on comparing three methods to derive information on cloud properties which can be run in conjunction with MAX-DOAS measurements, allowing for a more comprehensive characterisation of cloud effects: a ceilometer, an infrared camera and information derived from the MAX-DOAS measurements themselves. All instruments are located at the Max-Planck Institute for Chemistry in Mainz, Germany. We investigate, under which cloud conditions MAX-DOAS inversions might yield reasonable results and under which cloud conditions inversion results have large uncertainties. One focus of our investigation is the effect of cloud altitude on the MAX-DOAS retrievals.