Using the ESA eVe reference lidar system for the cal/val of lidar instruments onboard ESA satellite missions

The eVe lidar is ESA’s ground reference lidar system for the calibration and validation (cal/val) of ESA satellite missions. eVe is a combined linear/circular polarization lidar with Raman capabilities operating at 355 nm and deriving the profiles of the optical properties of aerosols and thin clouds, namely the particle backscatter and extinction coefficients, the lidar ratio, and the linear and circular depolarization ratios. The system is implemented in a dual-laser/dual-telescope configuration and it can be rotated to perform lidar measurements using different pointing geometries. As such, eVe can simultaneously reproduce the operation of any lidar system that uses linearly (e.g traditional polarization lidars; ATLID onboard EarthCARE mission) or circularly (e.g. ALADIN lidar onboard Aeolus mission) polarized emission.

The eVe lidar has been deployed in ASKOS, the ground-based component of the Joint Aeolus Tropical Atlantic Campaign in Cabo Verde (2021 and 2022), for performing targeted circular polarization lidar measurements for the validation of the Aeolus aerosol products (i.e. the Aeolus L2A products). The eVe-Aeolus comparisons reveal that the Aeolus co-polar backscatter coefficient is the most accurate L2A product followed by the noisier particle extinction coefficient with the larger discrepancies for the Aeolus profiles to be observed in lower altitudes where the aerosol load is larger. The Aeolus co-polar lidar ratio is the noisiest L2A product with the largest discrepancies from the corresponding eVe profiles. Currently the eVe lidar is under upgrade with main components of enabling the profiling of water vapor mixing ratio and extending the retrieval of the extinction coefficient towards daytime conditions, aiming to further enhance its measuring capabilities as well as to meet the requirements for the cal/val of the ATLID lidar products onboard EarthCARE mission which is currently in orbit. After the upgrade, eVe lidar will perform targeted measurements during the nearest EarthCARE overpasses from eVe’s location for the evaluation of the ATLID L2A products.

Acknowledgements:

This research is financially supported by the PANGEA4CalVal project (Grant Agreement 101079201) funded by the European Union and the “Best practice protocol for validation of Aerosol, Cloud, and Precipitation Profiles” ESA project (ACPV; Contract no. 4000140645/23/I-NS). The ASKOS campaign was funded by an ESA project (Contract no. 4000131861/20/NL/IA) and the acquired dataset can be accessed via https://evdc.esa.int/publications/askos-campaign-dataset/. The eVe lidar upgrade and the deployment for the cal/val of EarthCARE products are funded by an ESA project (Contract no. 4000146416/24/NL/FFi).