Validation of CALIPSO space-borne-derived attenuated backscatter coefficient profiles using a ground-based lidar in Athens, Greece

摘要

We present initial aerosol validation results of the space-borne lidarCALIOP -onboard the CALIPSO satellite- Level 1 attenuated backscattercoefficient profiles, using coincident observations performed with aground-based lidar in Athens, Greece (37.9° N, 23.6° E). Amulti-wavelength ground-based backscatter/Raman lidar system is operatingsince 2000 at the National Technical University of Athens (NTUA) in theframework of the European Aerosol Research LIdar NETwork (EARLINET), thefirst lidar network for tropospheric aerosol studies on a continental scale.Since July 2006, a total of 40 coincidental aerosol ground-based lidarmeasurements were performed over Athens during CALIPSO overpasses. Theground-based measurements were performed each time CALIPSO overpasses thestation location within a maximum distance of 100 km. The duration of theground–based lidar measurements was approximately two hours, centred on thesatellite overpass time. From the analysis of the ground-based/satellitecorrelative lidar measurements, a mean bias of the order of 22% fordaytime measurements and of 8% for nighttime measurements with respectto the CALIPSO profiles was found for altitudes between 3 and 10 km. Themean bias becomes much larger for altitudes lower that 3 km (of the order of60%) which is attributed to the increase of aerosol horizontalinhomogeneity within the Planetary Boundary Layer, resulting to theobservation of possibly different air masses by the two instruments. Incases of aerosol layers underlying Cirrus clouds, comparison results foraerosol tropospheric profiles become worse. This is attributed to thesignificant multiple scattering effects in Cirrus clouds experienced byCALIPSO which result in an attenuation which is less than that measured bythe ground-based lidar.