Cross-validations of the Aeolus aerosol products and new developments with airborne high-spectral-resolution lidar measurements above the tropical Atlantic during JATAC

Abstract

The Joint Aeolus Tropical Atlantic Campaign (JATAC) conducted in 2022 in Cabo Verde has provided quantitative lidar measurements, particularly from the NASA Langley High-Altitude Lidar Observatory (HALO) on board DC-8 aircraft, for process-level understanding of tropical dynamics, as well as for satellite validation. For the first time, the optical properties of particles (i.e. backscatter, extinction, attenuated backscatter coefficients, and depolarization ratios) have been measured for extended tropospheric sections collocated with the Aeolus satellite overpasses with limited geolocation and time offsets. This has contributed to the evaluation of the Aeolus Level-2A (L2A) aerosol optical properties product. In addition, localized aerosol profiles were measured by the ground-based multiwavelength Raman polarization and water vapour lidar Polly^XT. In this study, we assess the quality of the Aeolus L2A product retrieved with the standard correct algorithm (SCA) and the maximum likelihood estimation (MLE) as part of the September 2022 dataset reprocessed with the L2A processor, version 16. The focus is given to the 355 nm aerosol retrievals given at finer horizontal resolution, i.e. the so-called Aeolus measurement level at ≈ 18 km. They are compared to the 532 nm HALO airborne profiles that are converted to 355 nm using the backscatter Ångström exponent. HALO and Polly^XT polarization lidars also provide insights into the L2A algorithm’s limitations when looking at non-spherical particles such as Saharan dust. Even though it has no cross-polarized component, the Aeolus measurements can be corrected using collocated observations with such instruments that include both co-polarized and cross-polarized components of the backscattered light. Moreover the cross-validation with independent lidar measurements enables estimation of the lower limits for Aeolus backscatter detection.