| Popis: |
In the following, we report on the activities performed within the European Space Agency Quality Assurance for Earth Observation, QA4EO, project, Work Package 2191, titled Validation of ESA EO Aerosol Height products with EARLINET Lidar observations. The purpose of our study is to investigate the ability of the TROPOspheric Monitoring Instrument (TROPOMI) on board on the Sentinel-5P, to deliver accurate geometrical features of lofted aerosol layers in a continental scale. Comparisons with ground-based correlative measurements constitute a key component in the validation of passive satellite products related to aerosol properties. For this purpose, we use ground-based lidar data from lidar stations belonging to the European Aerosol Research Lidar, EARLINET, network. In the frame of this work, we have developed and applied an optimal methodology for validation purposes using EARLINET optical profiles a TROPOMI aerosol products, aiming at the investigation of Aerosol Layer Height product. This approach followed is based on the previous expertise and methodology that have been firstly developed and applied in EARLINET for the GOME-2/MetOp validation activities. We are looking for collocated cases between EARLINET and TROPOMI/SS5P overpasses for the time period 2018 – 2021, over the Mediterranean Basin which is selected as the domain of interest. We focus on selecting lidar stations located near the sea, because the ALH retrieval becomes unreliable over the land. Overall, for 7 selected EARLINET stations across the Mediterranean, 25 coincident aerosol cases were found, checked and flagged for the comparison against satellite retrievals. The presented validation methodology uses the lidar backscatter profiles and collocated TROPOMI ALH pixels for a standard set of collocation thresholds in time and space. We find high correlation (R2 =0.91) between satellite and ground-based data, but also that TROPOMI ALH values underestimate by -1.2±0.86 km on average the ground-based lidar observations for the selected cases with a remarkable aerosol load. The GOME-2 Absorbing Aerosol Height validation against EARLINET lidar profiles can be viewed in the relevant publication: Michailidis, K., Koukouli, M.-E., Siomos, N., Balis, D., Tuinder, O., Tilstra, L. G., Mona, L., Pappalardo, G., and Bortoli, D.: First validation of GOME-2/MetOp absorbing aerosol height using EARLINET lidar observations, Atmos. Chem. Phys., 21, 3193–3213, https://doi.org/10.5194/acp-21-3193-2021, 2021. |
