1. Generation of TOA Radiative Fluxes from the GERB Instrument Data. Part II: First Results Nicolas Clerbaux and GERB team Royal Meteorological Institute of Belgium EUMETSAT users conference – Weimar – 30 Sept. 2003

2. Content First result of using SEVIRI in the RMIB GERB data processing system: –NB -> BB conversions, –Scene identification, –Anisotropic factor for the radiance-to-flux conversions.

3. RMIB GERB/SEVIRI Overview Estimation of unfiltered reflected solar and emitted thermal radiative radiances and fluxes at the TOA from the SEVIRI: 1.NB-to-BB radiances 2.radiance-to-flux Comparison of BB radiance with GERB measurements -> SW and LW correction factors to apply to the SEVIRI radiances and fluxes.

4. SEVIRI NB->BB conversion Need: for the GERB unfiltering (cf. S. Dewitte presentation) and for the resolution enhancement of GERB data. Method: use of 2nd order regression on the NB radiances: Validation with the GERB BB radiance

5. Longwave Ratio GERB/SEVIRI GERB defective pixel

6. Shortwave Ratio GERB/SEVIRI SEVIRI overestimation over desert

7. SEVIRI Scene Identification Needed for the shortwave ADMs selection (surface type, cloud fraction, optical depth  and phase). Method: building of clear sky reflectance images for the SEVIRI VIS 0.6 and VIS 0.8  m (each 10 days) and analyse of the difference with actual NB reflectance. NIR 1.6 and IR for for cloud phase. TBD: aerosol and wind speed over clear ocean, fresh snow detection.

8. SEVIRI False Color Clear sky Reflectance Image R=  cs (0.8  m) G=  cs (0.8  m) B=  cs (0.6  m) Ref: A. Ipe et al., Pixel -Scale Composite TOA Clear-Sky Reflectances for Meteosat-7 Visible Data, Journal of Geophysical Research, in press.

9. 0.8  m 0.6  m Automatic selection of the more appropriated channel for cloud detection and cloud optical depth estimation: VIS 0.6 or VIS 0.8 ?

10. Cloud Optical Depth Retrieval Use of 24 look-up- tables: for: - VIS 0.6 and VIS 0.8 - 6 surface types - Ice and water clouds with: -  = actual reflectance -  cs = clear sky refl. -(  v  s  )=viewing geom.

11. Use of the 592 CERES-TRMM SW ADMs: Shortwave Angular Dependency Models

12. Ref: N. Clerbaux et al., Outgoing longwave flux estimation: improvement of angular modelling using spectral information, Rem. Sens.,2003, 85, 369-395. Longwave Angular Dependency Models with

13. Conclusions SEVIRI data looks fine (incl. calibration) NB->BB seems OK over most of the surfaces and cloud types but fails over desert (to be improved), Scene identification seems OK, Radiance-to-flux conversions: to be validated using CERES data on EOS Terra and Aqua satellites. Goal: processing of GERB using SEVIRI data operational for end of october 2003.