Assessment of CALIPSO attenuated backscatter and aerosol retrievals with a combined ground-based multi-wavelength lidar and sunphotometer measurement

Abstract

CALIPSO Level-1 attenuated backscatter and Level-2 aerosol products (Version-3.01) are evaluated with a combined ground-based lidar and AERONET-sunphotometer measurements in the daytime over the New York metropolitan area. To assess the CALIPSO Level-1 product, we combine the co-located ground-lidar and sunphotometer to derive aerosol extinction and backscatter profiles, and then simulate the CALIPSO equivalent attenuated backscatter coefficients. Direct statistical comparisons show a strong correlation (R = 0.92) and modest relative errors. Both dust and smoke plume events are focused to evaluate CALIPSO Level-2 aerosol layer products. The CALIPSO algorithms for cloud-aerosol discrimination and aerosol type classification are shown for the most part to work well, with a few exceptions in cases of aloft plumes with high aerosol loading. Small partitions of dense smoke are misclassified as the clouds or polluted dusts in the CALIPSO product. The aerosol extinction and backscatter coefficients are generally consistent between the CALIPSO and ground-based retrievals, but both geometric thickness and column optical depths of aerosol layers from CALIPSO products are underestimated. In addition, we find that some weakly scattering aerosol layers are clearly displayed by the ground-based lidar, but not identified by the current CALIPSO algorithm due to the detection sensitivity issue.