240 research outputs found
Validation of ESA EO Aerosol Height products with EARLINET Lidar observations
No full textIn 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
Geometrical characteristics of desert dust layers over Thessaloniki estimated with backscatter/Raman lidar and the BSC/DREAM model
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An update on the dynamically induced episodes of extreme low ozone values over the northern middle latitudes
No full textPerformance of the Aerosol Species Separation Algorithm (ASSA) Using Data from a Raman-Depolarization Lidar System at Thessaloniki, Greece
No full textThe aerosol species separation algorithm (ASSA) is a method designed to retrieve vertical concentration profiles of individual aerosol species by combining measurements from lidar systems and spectrophotometers. The ASSA operates as a forward model, simulating as the first step the attenuated backscatter and volume depolarization ratios at various wavelengths initially measured by lidar systems. Subsequently, it extends these simulations to reproduce radiance spectra obtained from co-located spectrophotometers by integrating a radiative transfer model. Currently, the ASSA relies on a lookup table (LUT) of intensive aerosol properties that correspond to mixtures generated from up to eight pure aerosol species as these are defined in the OPAC database. In this study we are focusing on the first step and investigating the performance of the algorithm when solely fitting nighttime data from the Thessaloniki lidar system are used. The algorithm identifies the ensemble of mixture/mass concentration combinations that best fit the elastic and Raman 4 primary species attenuated backscatter and depolarization ratio profiles
Validation of CALIPSO level-2 products using a ground based lidar in Thessaloniki, Greece
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Effect of Aerosols, Tropospheric NO<sub>2</sub> and Clouds on Surface Solar Radiation over the Eastern Mediterranean (Greece)
No full textIn this work, the effect that two basic air quality indexes, aerosols and tropospheric NO2, exert on surface solar radiation (SSR) is studied, along with the effect of liquid and ice clouds over 16 locations in Greece, in the heart of the Eastern Mediterranean. State-of-the-art satellite-based observations and climatological data for the 15-year period 2005–2019, and a radiative transfer system based on a modified version of the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model are used. Our SSR simulations are in good agreement with ground observations and two satellite products. It is shown that liquid clouds dominate, with an annual radiative effect (RE) of −36 W/m2, with ice clouds (−19 W/m2) and aerosols (−13 W/m2) following. The radiative effect of tropospheric NO2 is smaller by two orders of magnitude (−0.074 W/m2). Under clear skies, REaer is about 3–4 times larger than for liquid and ice cloud-covered skies, while RENO2 doubles. The radiative effect of all the parameters exhibits a distinct seasonal cycle. An increase in SSR is observed for the period 2005–2019 (positive trends ranging from 0.01 to 0.52 W/m2/year), which is mostly related to a decrease in the aerosol optical depth and the liquid cloud fraction
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