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We present initial aerosol validation results of the space-borne lidar CALIOP -onboard the CALIPSO satellite - Level 2
extinction coefficient profiles, using coincident observations performed with a ground-based lidar in Thessaloniki,
Greece (40.5° N, 22.9° E, 50m above sea level). A ground-based backscatter/Raman lidar system is operating since 2000
at the Laboratory of Atmospheric Physics (LAP) in the framework of the European Aerosol Research LIdar NETwork
(EARLINET), the first lidar network for tropospheric aerosol studies on a continental scale. Since July 2006, a total of
150 coincidental aerosol ground-based lidar measurements were performed over Thessaloniki during CALIPSO
overpasses. The ground-based measurements were performed each time CALIPSO overpasses the station location within
a maximum distance of 100 km. The duration of the ground-based lidar measurements was approximately two hours,
centred on the satellite overpass time. The analysis was performed for 4 different horizontal resolutions of 5, 25, 45 and
105 km. For our analysis we have used Atmospheric Volume Description (AVD) array to screen out everything that is
not an aerosol. Also, the cloud-aerosol discrimination (CAD) score, which provides a numerical confidence level for the
classification of layers by the CALIOP cloud-aerosol discrimination algorithm was set between -80 and -100. CALIPSO
extinction QC flags, which summarize the final state of the extinction retrieval, was also used. In our analysis we have
used those measurements where the lidar ratio is unchanged (extinction QC = 0) during the extinction retrieval or it the
retrieval is constrained (extinction QC = 1). The comparison was performed both for extinction and backscater
coefficient profiles. For clear sky conditions, the comparison shows good performances of the CALIPSO on-board lidar.
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