Aerosol retrievals from METEOSAT-8 - CM SAF

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SAF on Climate Monitoring Visiting Scientists Report Doc. No: 1.0 Issue : 1.0 Date : 4 October 2006 Previous generations of geostationary meteorological satellites, such as METEOSAT and GOES have been widely used to monitor aerosol properties over oceans (Moulin et al., 1997). However, the spectral channels of the first generation METEOSAT were rather limited for accurate retrievals of aerosol parameters. More advanced aerosol retrievals have been done with polar orbiting satellites such as NOAA-AVHRR, MERIS, SEAWIFS and MODIS (Ramon 2001, Ramon 2004,and Kaufman and Tanre, 1997). The Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat Second Generation operates channels in the visible and near IR wavelength regions that are similar to e.g. NOAA-AVHRR and MODIS. Therefore, the launch of the MSG family is a great opportunity to test new ideas for filling the gap between retrievals from geostationary and polar orbiting satellites, as SEVIRI combines the specific advantages of the geostationary orbit and geometric, radiometric and spectroscopic capabilities of the NOAA/AVHRR family. The objective of this Visiting Scientist activity is to perform a user requirement and feasibility study to catch the main steps of a future operational algorithm for retrieving the aerosol optical properties over land from the MSG/SEVIRI instrument. For the feasibility study we kept the shortest time resolution available from MSG i.e. 15 minutes. This constraint could be relaxed in the future but we wanted to start with the strongest constraint. The short time for this study forced us to restrict ourselves to the main difficulty of all aerosol retrieval algorithms that are applied over land surfaces, i.e. the removal of the surface contribution to the satellite signal. This is needed for all existing sensors and aerosol retrieval algorithms. In this study our approach is to demonstrate, mainly through real data analysis, that the core idea of this future algorithm is correct and that significant results are achievable with very simple assumptions. However, the output of this study should not be taken neither as an Algorithm Theoretical Basis Document nor an algorithm specification document. A lot of crude assumptions have to be refined in order to reach a complete and robust algorithm. A very recent paper under press and not available at the beginning of the work draws very similar conclusions as ours but for the GOES sensor (Knapp et al. 2005). The user requirements for an aerosol product over land from SEVIRI are detailed in chapter 3. In chapter 4 the main algorithm classes and performances are briefly reviewed. Then we will explain in chapter 5 our methodology and show some first results. We will end in chapter 6 with giving some research directions and list all potential improvements we foresee at the moment. - 4 -
SAF on Climate Monitoring Visiting Scientists Report Doc. No: 1.0 Issue : 1.0 Date : 4 October 2006 4 User requirements 4.1 Needs from Climate researches Tropospheric aerosols are important components of the earth-atmosphere and ocean system. They affect climate through three primary processes. First, direct radiative forcing results when radiation is scattered or absorbed by the aerosols itself. Second, indirect radiative forcing results when enhanced concentrations of aerosols modify cloud properties. And finally, aerosols can have an indirect effect on heterogeneous chemistry, which in turn can influence climate by modifying concentration of climate-influencing constituents such as greenhouse gases. Frequent observations during the day can improve characterization of aerosols contents because of their temporal and dynamical variability. Frequent observations of aerosols are also desirable for aviation, air pollution and quality and health applications. In spite of advances in aerosol remote sensing (King et al., 1999), most retrievals are limited to twice per day, by using the morning and afternoon passes of the orbiting polar satellites. Aerosols, however, show diurnal variations that are missed by such sparse observations. For example, to monitor air quality and for human health goals it is important to understand aerosol plume movement to track and forecast the plume movement and its temporal evolution. 4.2 Needs from SAFs 4.2.1 CM-SAF The Satellite Application Facility on Climate Monitoring (CM-SAF) generates and archives high quality data sets satellite products using EUMETSAT and National Oceanic and Atmospheric Administration (NOAA) satellites for climate research. The CM-SAF products are generated in near-real time and comprise surface albedo, humidity, clouds and radiation products. The surface albedo and radiation product algorithms correct for atmospheric distortions caused by aerosols. For the aerosol, model computed single scattering albedo, asymmetry factor and aerosol optical thickness are used. The information on the spatial variations in aerosol properties is taken from OPAC/GADS climatology (Hess et al. 1998, Koepke et al. 1997). The cloud detection and - 5 -
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Aerosol retrievals from METEOSAT-8 - CM SAF

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