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CALIOP AEP

CALIOP Clear-Sky Constrained Aerosol Extinction Profiles

Current operational CALIOP aerosol extinction profile retrievals usually rely on accurately specifying the relationship between aerosol extinction and backscattering (i.e. lidar ratio). Uncertainties in the assigned lidar ratios are typically the largest source of systematic error (~30-50%) in the CALIOP retrievals of aerosol extinction, backscatter, and aerosol optical depth. Alternatively, column aerosol optical depth (AOD) can be used to solve the lidar equation and obtain column-equivalent lidar ratios and retrieve aerosol extinction profiles from the CALIOP attenuated backscatter profiles. These derived lidar ratios correspond to the aerosols in the altitude range from 0-7 km.

Data Centers

ASDC

Overview

Clear-sky column-equivalent aerosol lidar ratios and aerosol extinction profiles are derived from CALIOP attenuated backscatter profiles constrained using co-located column AODs provided by: 1) CALIOP Ocean-Derived Column Optical Depth (ODCOD), 2) MODIS Dark Target/Deep Blue (DT/DB) (Collection 6) retrievals, and the 3) Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) model. The column AODs from the first two sources are derived from satellite measurements while the column AOD values from item 6 are from a reanalysis which assimilates AOD from MODIS, MISR, and AERONET measurements. These  CALIOP constrained aerosol extinction profiles have been evaluated using the extensive record of coincident and co‑located airborne High Spectral Resolution Lidar (HSRL) data acquired during more than 150 CALIPSO underflights since 2006. Each of these AOD constraints leads to clear-sky aerosol extinction values that are on average in agreement with HSRL aerosol extinction values with mean bias differences within 0.01 km‑1 and 10%. Moreover, aerosol extinction profiles derived using these AOD constraints have on average smaller bias and RMS differences than the operational CALIOP V4.51 retrievals; these constrained aerosol extinction profiles have bias and root-mean-square differences nearly a factor of two smaller than differences computed using the CALIOP V4.51 operational aerosol extinction retrievals. 

These CALIOP constrained clear-sky aerosol extinction profiles have been computed globally using these three AOD constraints: 1) MODIS DT/DB AOD for CALIOP daytime data acquired between 2006-2018 and, 2) MERRA-2 AOD for CALIOP daytime and nighttime data acquired between 2006-2023.  Since the MERRA-2 AOD values are available for the entire CALIOP data record during both day and night and over both land and water, they enable an extensive global record of constrained CALIOP clear-sky aerosol extinction profiles. These clear-sky CALIOP aerosol extinction profiles derived using these AOD constraints will be valuable for several studies, such as deriving PM2.5 concentrations and for reducing uncertainties in observational estimates of aerosol direct radiative forcing. 


 

Related Instruments

Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) CALIOP is a two-wavelength lidar that provides high-resolution vertical profiles of aerosols and clouds.
Moderate Resolution Imaging Spectroradiometer (MODIS) The Moderate Resolution Imaging Spectroradiometer continually collects data in 36 spectral channels with global coverage every 1 to 2 days.