Case studies and comparisons of the CALIPSO aerosol optical depth measurements and aerosol type estimates

Abstract

The CALIPSO Level II data are analyzed to assess the veracity of the CALIPSO aerosol type identification algorithm and generate distributions of aerosol types and their respective optical characteristics. The distributions show that the classification algorithm has no surface type or diurnal dependencies. For this initial assessment of algorithm performance, we analyze global distributions of the CALIPSO aerosol types, along with distributions of integrated attenuated backscatter, backscatter color ratio, and volume depolarization ratio for each type. The aerosol type distributions are further partitioned according to various geophysical discriminators (e.g., geographic region, land vs. ocean, and day vs. night). The algorithm generates the expected results in most scenes. The total color ratio distributions show significant overlap between the aerosol types. Since the aerosol typing algorithm uses a logical decision tree based on fixed thresholds, we test the sensitivity of the typing algorithm to perturbations in these threshold values. To test the CALIPSO extinction to backscatter ratio estimates, we compare extinction-to-backscatter ratios derived using the transmittance method to the values in the look up tables.