ABSTRACT:The EUMETSAT Satellite Application Facility for Land Surface Analysis operationally delivers estimates of the downwelling shortwave radiation flux, which constitutes an important variable for characterising the surface energy budget. The product is derived from observations provided by the SEVIRI instrument onboard the geostationary satellites of the Meteosat Second Generation series. The spatial coverage of the product includes Europe, Africa, the Middle East, and parts of South America. It is generated every 30 min and distributed to the users in near real-time. For clear sky conditions the flux estimate is determined with a parameterisation of the atmospheric transmittance as a function of the concentration of atmospheric constituents. For overcast sky a simple physical model of the radiation transfer in the cloudatmosphere-surface system is employed, for which the satellite signal supplies the essential input information. The product has been validated with in situ data from six European ground measurement stations. The resulting statistics show a standard deviation of the difference between instantaneous satellite estimates and ground measurements in the order of 40 W m −2 for clear sky data and 110 W m −2 for cloudy sky data. For the complete sample including all data points the standard deviation amounts to 85 W m −2 . The bias between the satellite product and the ground data is small with absolute values of less than 10 W m −2 .
The European Space Agency will launch the Atmospheric Laser Doppler Instrument (ALADIN) for global wind profile observations in the near future. The potential of ALADIN to measure the optical properties of aerosol and cirrus, as well, is investigated based on simulations. A comprehensive data analysis scheme is developed that includes (a) the correction of Doppler-shifted particle backscatter interference in the molecular backscatter channels (cross-talk effect), (b) a procedure that allows us to check the quality of the cross-talk correction, and (c) the procedures for the independent retrieval of profiles of the volume extinction and backscatter coefficients of particles considering the height-dependent ALADIN signal resolution. The error analysis shows that the particle backscatter and extinction coefficients, and the corresponding extinction-to-backscatter ratio (lidar ratio), can be obtained with an overall (systematic+statistical) error of 10%-15%, 15%-30%, and 20%-35%, respectively, in tropospheric aerosol and dust layers with extinction values from 50 to 200 Mm(-1); 700-shot averaging (50 km horizontal resolution) is required. Vertical signal resolution is 500 m in the lower troposphere and 1000 m in the free troposphere. In cirrus characterized by extinction coefficients of 200 Mm(-1) and an optical depth of >0.2, backscatter coefficients, optical depth, and column lidar ratios can be obtained with 25%-35% relative uncertainty and a horizontal resolution of 10 km (140 shots). In the stratosphere, only the backscatter coefficient of aerosol layers and polar stratospheric clouds can be retrieved with an acceptable uncertainty of 15%-30%. Vertical resolution is 2000 m.
We introduce the Hybrid End-To-End Aerosol Classification (HETEAC) model for the upcoming EarthCARE mission. The model serves as the common baseline for development, evaluation, and implementation of EarthCARE algorithms. It shall ensure the consistency of different aerosol products from the multi-instrument platform as well as facilitate the conform specification of broad-band optical properties necessary for the EarthCARE radiative closure efforts. The hybrid approach ensures the theoretical description of aerosol microphysics consistent with the optical properties of various aerosol types known from observations. The end-to-end model permits the uniform representation of aerosol types in terms of microphysical, optical and radiative properties.
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