Characterisation of dust aerosols from ALADIN and CALIOP measurements

Abstract

Abstract. Atmospheric aerosols have a pronounced effect on climate dynamics at both regional and global scales, but the magnitude of these effects is subject to considerable uncertainties. A major contributor to these uncertainties is the incomplete understanding of aerosol's vertical structure, largely due to observational limitations. Spaceborne lidars can directly observe the vertical distribution of aerosols globally, and are increasingly used in atmospheric aerosol remote sensing. As the first spaceborne High Spectral Resolution Lidar (HSRL), the ALADIN instrument onboard the Aeolus satellite was operational from 2018 to 2023. With its sophisticated design, ALADIN can retrieve aerosol backscatter and extinction coefficients separately without an assumption of the lidar ratio. This study is dedicated to assessing the performance of ALADIN's aerosol retrieval capabilities by comparing them with CALIOP measurements. A statistical analysis of retrievals from both instruments during the June 2020 Saharan dust event indicates good consistency between the observed backscatter and extinction coefficients. A detailed comparison of extinction coefficients for dust layers reveals that ALADIN is more susceptible to signal attenuation than CALIOP. During this extreme dust event, CALIOP-derived aerosol optical depth (AOD) exhibited large discrepancies with MODIS Aqua measurements. Using collocated ALADIN observations to revise the dust lidar ratio to 63.5 sr, AODs retrieved from CALIOP are increased by 46 %, improving the comparison with MODIS data. Further, the combination of measurements from ALADIN and CALIOP can enhance the tracking of aerosols' vertical transport. This study demonstrates the potential for spaceborne HSRL to retrieve aerosol optical properties. It highlights the benefits of spaceborne HSRL in directly obtaining the lidar ratio, significantly reducing uncertainties in extinction retrievals. This work paves the way for forthcoming spaceborne HSRL missions, particularly the ESA ATLID space lidar (set for a 2024 launch) and Aeolus-2.

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

“…SCA middle bin aerosol product with CALIPSO. Song et al (2023) found that using the dust lidar ratio of 63.5 sr derived from collocated Aeolus data (L2A SCA middle bin), aerosol optical thickness values retrieved from CALIOP were increased by 46%, which improved the comparison with MODIS data. This suggests that the AEL-PRO retrieved lidar ratios are reasonable for the aerosol scenes.…”

“…11. A Gaussian function is fitted to get the center of the distribution at about 63 sr. A similar lidar ratio value was employed by Song et al (2023) in their evaluation of the Aeolus L2A…”