Evaluation of Aeolus feature mask and particle extinction coefficient profile products using CALIPSO data.

The Atmospheric LAser Doppler INstrument (ALADIN) on board Aeolus was the first high-spectral-resolution lidar (HSRL) in space. It was launched in 2018 and re-entered in 2023. The FeatureMask (A-FM) and extinction profile algorithms (A-PRO) developed for the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) HSRL ATmospheric LIDar (ATLID) have been adapted to Aeolus and called AEL-FM and AEL-PRO, respectively. These algorithms have been purposely built to process low signal-to-noise ratio space-based lidar signals. A short description of the AEL-FM and AEL-PRO algorithms is provided in this paper. AEL-FM and AEL-PRO prototype products (v1.7) have been evaluated using the collocated Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) vertical feature mask (VFM) product and level 2 aerosol profile product for 2 months of data in October 2018 and May 2019. Aeolus and CALIPSO are both polar-orbiting satellites, but they have different overpass times. The evaluations are focused on desert dust aerosols over Africa. These types of scenes are often stable in space (tens of kilometres) and time (on the order of 0.5–1 h), and thus, a useful number of collocated cases can be collected. We have found that the AEL-FM feature mask and the CALIPSO VFM show similar aerosol patterns in the collocated orbits, but AEL-FM does not separate aerosol and cloud features. Aeolus and CALIPSO have a good agreement for the extinction coefficients for the dust aerosols, especially for the cloud-free scenes. The Aeolus aerosol optical thickness (AOT) is larger than the CALIPSO AOT, mainly due to cloud contamination. Because of the missing a cross-polar channel, it is difficult to distinguish aerosols and thin ice clouds using the Aeolus extinction coefficients alone. The AEL-FM and AEL-PRO algorithms have been implemented in the Aeolus level 2A (L2A) processor. The findings here are applicable to the AEL-FM and AEL-PRO products in L2A Baseline 17. This is the first time that the AEL-FM and AEL-PRO products have been evaluated using CALIPSO data. [ABSTRACT FROM AUTHOR]