Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using a ground-based lidar in Seoul, Korea

摘要

We present initial validation results of the space-borne lidar CALIOPonboard CALIPSO satellite using coincidental observations from aground-based lidar in Seoul National University (SNU), Seoul, Korea(37.46° N, 126.95° E). We analyze six selected cases between September2006 and February 2007, including 3 daytime and 3 night-time observationsand covering different types of clear and cloudy atmospheric conditions.Apparent scattering ratios calculated from the two lidar measurements oftotal attenuated backscatter at 532 nm show similar aerosol and cloud layerstructures both under cloud-free conditions and in cases of multiple aerosollayers underlying semi-transparent cirrus clouds. Agreement on top and baseheights of cloud and aerosol layers is generally within 0.10 km,particularly during night-time. This result confirms that the CALIPSOscience team algorithms for the discrimination of cloud and aerosol as wellas for the detection of layer top and base altitude provide reliableinformation in such atmospheric conditions. This accuracy of the planetaryboundary layer top height under cirrus cloud appears, however, limitedduring daytime. Under thick cloud conditions, however, information on thecloud top (bottom) height only is reliable from CALIOP (ground-based lidar)due to strong signal attenuations. However, simultaneous space-borne CALIOPand ground-based SNU lidar (SNU-L) measurements complement each other andcan be combined to provide full information on the vertical distribution ofaerosols and clouds. An aerosol backscatter-to-extinction ratio (BER) estimatedfrom lidar and sunphotometer synergy at the SNU site during the CALIOPoverpass is assessed to be 0.023±0.004 sr (i.e. a lidar ratio of43.2±6.2 sr) from CALIOP and 0.027±0.006 sr (37.4±7.2 sr)from SNU-L. For aerosols within the planetary boundary layer undercloud-free conditions, the aerosol extinction profiles from both lidars arein agreement within about 0.02 km. Under semi-transparent cirrusclouds, such profiles also show good agreement for the night-time CALIOPflight, but large discrepancies are found for the daytime flights due to asmall signal-to-noise ratio of the CALIOP data.