Abstract
Abstract. The Spinning Enhanced Visible and InfraRed Imager (SEVIRI) aboard Meteosat Second Generation (MSG) launched in 2003 by EUMETSAT is dedicated to the Nowcasting applications and Numerical Weather Prediction and to the provision of observations for climate monitoring and research. We use the data in visible and near infrared (NIR) channels to derive the aerosol optical thickness (AOT) over land. The algorithm is based on the assumption that the top of the atmosphere (TOA) reflectance increases with the aerosol load. This is a reasonable assumption except in case of absorbing aerosols above bright surfaces. We assume that the minimum in a 14-days time series of the TOA reflectance is, once corrected from gaseous scattering and absorption, representative of the surface reflectance. The AOT and the aerosol model (a set of 5 models is used), are retrieved by matching the simulated TOA reflectance with the TOA reflectances measured by SEVIRI in its visible and NIR spectral bands. The high temporal resolution of the data acquisition by SEVIRI allows to retrieve the AOT every 15 min with a spatial resolution of 3 km at sub-satellite point, over the entire SEVIRI disk covering Europe, Africa and part of South America. The resulting AOT, a level 2 product at the native temporal and spatial SEVIRI resolutions, is presented and evaluated in this paper. The AOT has been validated using ground based measurements from AErosol RObotic NETwork (AERONET), a sun-photometer network, focusing over Europe for 3 months in 2006. The SEVIRI estimates correlate well with the AERONET measurements, r = 0.64, with a slight overestimate, bias = −0.017. The sources of errors are mainly the cloud contamination and the bad estimation of the surface reflectance. The temporal evolutions exhibited by both datasets show very good agreement which allows to conclude that the AOT Level 2 product from SEVIRI can be used to quantify the aerosol content and to monitor its daily evolution with a high temporal frequency. The comparison with daily maps of Moderate Resolution Imaging Spectroradiometer (MODIS) AOT level 3 product shows qualitative good agreement in the retrieved geographic patterns of AOT. Given the high spatial and temporal resolutions obtained with this approach, our results have clear potential for applications ranging from air quality monitoring to climate studies. This paper presents a first evaluation and validation of the derived AOT over Europe in order to document the overall quality of a product that will be made publicly available to the users of the aforementioned research communities.
Highlights
Tropospheric aerosols which are solid or liquid particles suspended in the air (Junge, 1958; Whitby, 1976), have two origins: natural and anthropogenic
We focused the validation over the Europe for three months in 2006 (March, April and July), and selected 43 stations for which aerosol optical thickness is available for at least one month
We use the information of the quality assurance mask to filter the level 2 aerosol optical thickness and keep the most confident pixels to compare with measurements from the ground
Summary
Tropospheric aerosols which are solid or liquid particles suspended in the air (Junge, 1958; Whitby, 1976), have two origins: natural and anthropogenic. The origin of the cloud formation being the presence in the atmosphere of cloud condensation nuclei (CCN) around which water vapour condensates, an increase of CCN can affect cloud microphysics and cloud physics (formation, evolution, dissipation) (Denman et al, 2007; Haywood and Boucher, 2000; Schwartz and Slingo, 1995; Hegg et al, 1993) These first and second indirect effects are currently a source of major uncertainties in cloud and climate models (Ghan et al, 2001; Hansen et al, 1997; Quaas et al, 2008; Schulz et al, 2006; Lohmann et al, 2010).
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