Validation of the TROPOMI/S5P aerosol layer height using EARLINET lidars

[摘要] The purpose of this study is to investigate the ability of the Sentinel-5PTROPOspheric Monitoring Instrument (TROPOMI) to derive accurate geometricalfeatures of lofted aerosol layers, selecting the MediterraneanBasin as the study area. Comparisons with ground-based correlative measurements constitute akey component in the validation of passive and active satellite aerosolproducts. For this purpose, we use ground-based observations from quality-controlled lidar stations reporting to the European Aerosol Research LidarNetwork (EARLINET). An optimal methodology for validation purposes has beendeveloped and applied using the EARLINET optical profiles and TROPOMIaerosol products, aiming at the in-depth evaluation of the TROPOMI aerosollayer height (ALH) product for the period 2018 to 2022 over theMediterranean Basin. Seven EARLINET stations were chosen, taking intoconsideration their proximity to the sea, which provided 63 coincidentaerosol cases for the satellite retrievals. In the following, we present thefirst validation results for the TROPOMI/S5P ALH using the optimizedEARLINET lidar products employing the automated validation chain designedfor this purpose. The quantitative validation at pixels over the selectedEARLINET stations illustrates that the TROPOMI ALH product is consistent withthe EARLINET lidar products, with a high correlation coefficient R =0.82 ( R =0.51 ) and a mean bias of - 0.51 ± 0.77  km and - 2.27 ± 1.17  kmover ocean and land, respectively. Overall, it appears that aerosol layeraltitudes retrieved from TROPOMI are systematically lower than altitudesfrom the lidar retrievals. High-albedo scenes, as well as low-aerosol-loadscenes, are the most challenging for the TROPOMI retrieval algorithm, andthese results testify to the need to further investigate the underlyingcause. This work provides a clear indication that the TROPOMI ALH productcan under certain conditions achieve the required threshold accuracy and precisionrequirements of 1 km, especially when only ocean pixels are included in thecomparison analysis. Furthermore, we describe and analyse three case studiesin detail, one dust and two smoke episodes, in order to illustrate thestrengths and limitations of the TROPOMI ALH product and demonstrate thepresented validation methodology. The present analysis provides importantadditions to the existing validation studies that have been performed so farfor the TROPOMI S5P ALH product, which were based only onsatellite-to-satellite comparisons.

[学科分类] 医学（综合）