Ceilometer aerosol profiling vs. Raman lidar in the frame of INTERACT campaign of ACTRIS

Abstract

Despite their differences from more advanced and more powerful lidars, the low con-struction and operation cost of ceilometers, originally designed for cloud base height monitoring, has fostered their use for the quantitative study of aerosol properties. The large number of ceilometers available worldwide represents a strong motivation to in-5 vestigate both the extent to which they can be used to fill in the geographical gaps between advanced lidar stations and also how their continuous data flow can be linked to existing networks of the more advanced lidars, like EARLINET (European Aerosol Research LIdar NETwork). In this paper, multi-wavelength Raman lidar measurements are used to investigate 10 the capability of ceilometers to provide reliable information about atmospheric aerosol content through the INTERACT (INTERcomparison of Aerosol and Cloud Track-ing) campaign carried out at the CNR-IMAA Atmospheric Observatory (760 m a.s.l., 40.60 • N, 15.72 • E), in the framework of ACTRIS (Aerosol Clouds Trace gases Re-search InfraStructure) FP7 project. This work is the first time that three different com-15 mercial ceilometers with an advanced Raman lidar are compared over a period of six months. The comparison of the attenuated backscatter profiles from a multi-wavelength Raman lidar and three ceilometers (CHM15k, CS135s, CT25K) reveals differences due to the expected discrepancy in the SNR but also due to effect of changes in the ambient temperature on the short and mid-term stability of ceilometer calibration. A large insta-20 bility of ceilometers in the incomplete overlap region has also been observed, making the use of a single overlap correction function for the whole duration of the campaign critical. Therefore, technological improvements of ceilometers towards their operational use in the monitoring of the atmospheric aerosol in the low and free troposphere are needed.