Abstract
CALIPSO (Cloud-Aerosol Lidar and Pathfinder Satellite Observations) Level 3 (CL3) data were compared against EARLINET (European Aerosol Research Lidar Network) monthly averages obtained by profiles during satellite overpasses. Data from EARLINET stations of Evora, Granada, Leipzig, Naples and Potenza, equipped with advanced multi-wavelength Raman lidars were used for this study. Owing to spatial and temporal differences, we reproduced the CL3 filtering rubric onto the CALIPSO Level 2 data. The CALIPSO monthly mean profiles following this approach are called CALIPSO Level 3*, CL3*. This offers the possibility to achieve direct comparable datasets. In respect to CL3 data, the agreement typically improved, in particular above the areas directly affected by the anthropogenic activities within the planetary boundary layer. However in most of the cases a subtle CALIPSO underestimation was observed with an average bias of 0.03 km-1. We investigated the backscatter coefficient applying the same screening criteria, where the mean relative difference in respect to the extinction comparison improved from 15.2% to 11.4%. Lastly, the typing capabilities of CALIPSO were assessed outlining the importance of the correct aerosol type (and associated lidar ratio value) assessment to the CALIPSO aerosol properties retrieval.
Highlights
The CL3 product aims at characterizing the global 3-D distribution of aerosol as well as aerosol seasonal and interannual variations, and assisting aerosol models
The CL3 data were compared against EARLINET profiles, the correlative measurements regime and the CALIPSO mapping scheme combined with variable and unfavorable atmospheric conditions resulted in a very dissimilar number of collected observations, namely 272 CALIPSO overflights and 96 EARLINET correlative measurements
The mean relative extinction bias for the range 1-3 km is 40% while for backscatter is limited to 15%. This CALIPSO underestimation is in agreement with what observed for Potenza already in CALIPSO Level 1 data [7]
Summary
The CL3 product aims at characterizing the global 3-D distribution of aerosol as well as aerosol seasonal and interannual variations, and assisting aerosol models. The main outputs are profiles of aerosol extinction coefficient at 532 nm and its vertical integral (aerosol optical depth; AOD). CL3 data are mapped onto a globally uniform 2◦x5◦ (latitude x longitude) grid cell. The vertical resolution of the product is 60 m over the range of the heights -0.5 km to 12 km relative to the mean sea level. Mean extinction profiles are computed for four conditions: nighttime/daytime all-sky and cloud-free. Several quality control flags contained in the Level 2 files are used to screen the data prior to averaging. A detailed summary of the methodology used for the production of the CL3 product is provided in the Appendix of [1]
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