First validation of GOME-2/MetOp absorbing aerosol height using EARLINET lidar observations

Abstract

Abstract. The aim of this study is to investigate the potential of the Global Ozone Monitoring Experiment-2 (GOME-2) instruments, aboard the Meteorological Operational (MetOp)-A, MetOp-B and MetOp-C satellite programme platforms, to deliver accurate geometrical features of lofted aerosol layers. For this purpose, we use archived ground-based lidar data from stations available from the European Aerosol Research Lidar Network (EARLINET) database. The data are post-processed using the wavelet covariance transform (WCT) method in order to extract geometrical features such as the planetary boundary layer (PBL) height and the cloud boundaries. To obtain a significant number of collocated and coincident GOME-2 – EARLINET cases for the period between January 2007 and September 2019, 13 lidar stations, distributed over different European latitudes, contributed to this validation. For the 172 carefully screened collocations, the mean bias was found to be −0.18 ± 1.68 km, with a near-Gaussian distribution. On a station basis, and with a couple of exceptions where very few collocations were found, their mean biases fall in the ± 1 km range with an associated standard deviation between 0.5 and 1.5 km. Considering the differences, mainly due to the temporal collocation and the difference, between the satellite pixel size and the point view of the ground-based observations, these results can be quite promising and demonstrate that stable and extended aerosol layers as captured by the satellite sensors are verified by the ground-based data. We further present an in-depth analysis of a strong and long-lasting Saharan dust intrusion over the Iberian Peninsula. We show that, for this well-developed and spatially well-spread aerosol layer, most GOME-2 retrievals fall within 1 km of the exact temporally collocated lidar observation for the entire range of 0 to 150 km radii. This finding further testifies for the capabilities of the MetOp-borne instruments to sense the atmospheric aerosol layer heights.

Validation of the TROPOMI/S5P Aerosol Layer Height using EARLINET lidars

“…The methodology is demonstrated using a selected number of collocated cases of TROPOMI overpasses over 215 selected EARLINET lidar stations located around the Mediterranean Basin for the period June 2018 to September 2021. The approach followed is based on the previous expertise and methodology that have been developed using EARLINET observations for the GOME2/MetOp validation activities (Michailidis et al, 2021). At present, seven EARLINET stations operating at 1064 nm (or 532 nm) channel contribute to this study (Figure 1).…”

“…With respect to the aerosol layer height reported by UV-VIS satellite sensors,Michailidis et al, (2021) have successfully validated the GOME2/MetOp Absorbing aerosol height (AAH) products using aerosol profiles reported by the EARLINET community. The intercomparison showed that the GOME-2 AAH measurements provide a good estimation of the aerosol layer altitudes sensed by the EARLINET ground-based lidars with a 165 mean bias of approximately −0.2±1.7 km.…”

“…geographic and temporal coverage of EARLINET stations along their quality assured measurements provides an excellent framework for the intercomparison of TROPOMI/S5P products under different atmospheric conditions and aerosol concentrations around Europe. The GOME2/MetOp aerosol height products have also 85 been validated against the EARLINET ground-based lidars (Michailidis et al, 2021). At the time of writing this article, no studies assessing the calibration and validation of TROPOMI aerosol products with ground-based…”

“…Following the work proposed by Michailidis et al (2021) for automatic layer detection, we also apply the WCT (Wavelet Covariance Transform) approach in order to check whether the TROPOMI retrieved ALH is sensitive to distinct layers rather than a representative effective layer from the whole profile. In this methodology, described in Appendix A2, all possible individual layers identified by the lidar observations are analysed autonomously, providing individual assessments on the height of the aerosol mass, and not a mean effective 275 height from all layers as is extracted by Eq.…”

Towards Early Detection of Tropospheric Aerosol Layers Using Monitoring with Ceilometer, Photometer, and Air Mass Trajectories

“…The aerosol layers in free troposphere (FT) can be considered as a proxy for their potential to enter PBL and, thus, can directly affect human activity. On the other hand, it is a reliable dataset when used for the validation of the aerosol layer height (ALH) retrieved from satellites (e.g., [7,8]) and of chemistry transport models [9]. Furthermore, they can provide a warning for aviation (e.g., [10]).…”