1. Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processing Nicolas Clerbaux & RMIB GERB Team. GIST 26, RAL 3 and 4 May 2007

2. MSG1 -> MSG2 transition New GERB instrument but also new SEVIRI imager Are the SEVIRI scene identifications consistent? –GERB unfiltering –GERB SW ADM selection –GERB LW angular modelling –GERB scene identification –GERB dust flag and AOD retrieval Are the GERB-likes (SEVIRI NB-to-BB) consistent? –RGP GERB geolocation –GERB unfiltering –GERB resolution enhancement –use of GERB-like data for monthly means

3. Structure of the talk Intercomparison of level 1.5 SEVIRI data –reflectance for visible channels –BT and radiance for thermal channels Intercomparison of GERB scene identification –cloud fraction, –cloud optical depth –cloud phase –clear sky reflectance –LW anisotropic factor –dust flag and AOD retrieval Intercomparison of the GERB-like BB quantities –solar and thermal radiances –solar and thermal fluxes Conclusions

4. The MSG1 and MSG2 data look very similar... “natural color”“air mass”

5. Visible bands spectral response and effective central wavelength for MSG-1 and MSG-2 MSG  s =0.639µm MSG2  s =0.640µm MSG  s =0.809µm MSG2  s =0.807µm MSG  s =1.635µm MSG2  s =1.635µm

6. 0.6 µm reflectance intercomparison ratio MSG2/MSG1

7. 0.6 µm reflectance intercomparison – saturations for MSG2 Max 0.6 µm reflectance at nadir and d=1 A.U. is MSG1 : 1.082 MSG2 : 0.942 Software fix: accept saturation if SZA<20 °

8. 0.8 µm reflectance intercomparison ratio MSG2/MSG1

9. 1.6 µm reflectance intercomparison ratio MSG2/MSG1

10. 6.2 µm brightness temperature intercomparison ratio MSG2/MSG1

11. 7.3 µm brightness temperature intercomparison ratio MSG2/MSG1

12. 8.7 µm brightness temperature intercomparison ratio MSG2/MSG1

13. 9.7 µm brightness temperature intercomparison ratio MSG2/MSG1

14. 10.8 µm brightness temperature intercomparison ratio MSG2/MSG1

15. 12 µm brightness temperature intercomparison ratio MSG2/MSG1

16. 13.4 µm brightness temperature intercomparison ratio MSG2/MSG1

17. Spectral radiance comparison ratio MSG2/MSG1 WV 6.2 : 1.002 WV 7.3 : 0.992 IR 8.7 : 0.999 IR 9.7 : 0.994 IR 10.8 : 1.000 IR 12.0 : 0.996 IR 13.4 : 0.974 -> in general MSG-2 is close or a bit lower than MSG-1, CO2 is significantly lower

18. Summary for level 1.5 MSG-2/MSG-1 intercomparison visible 0.6µm and 0.8µm channels : 1 to 2% higher reflectance near IR channel (1.6µm): very close thermal channels: very close or a bit lower except the CO2 channel (13.4µm) which is significantly colder (0.5% in BT, 2.5% in radiance) 0.6µm is often saturated over thick cloud residual stripes in the WV 6.2µm channel

19. Intercomparison of scene identification surface type is exactly the same (same rectification grid) cloud fraction cloud optical depth cloud phase clear sky reflectance images LW angular modeling Helen Brindley 's dust flag Aerosol retrieval with Ignatov look-up-table for the 0.6µm, 0.8µm and 1.6µm channels

20. Cloud fraction

21. Cloud optical depth (log)

22. Cloud phase (0=pure water 1=pure ice)

23. Clear sky reflectance intercomparison (ratio to model) VIS 0.6VIS 0.8

24. LW ADM due to the change in NB radiances F=  L / R( ,L 6.2, L 10.8, L 12,L 13.4 ) F MSG1' /F MSG1 Ratio of the flux for a same BB radiance L but for simulated differences between MSG1 and MSG2 NB radiances in the 6.2µm, 10.8µm, 12µm, 13.4µm channels Small increase of the anisotropy (0.2%).

25. MSG2 MSG1 Dust Flag

26. AOD in 0.6 µm channel

27. AOD in 0.8 µm channel

28. AOD in 1.6 µm channel

29. Summary for scene identification cloud fraction very similar cloud optical depth slightly higher (2%) due to the 0.6µm and 0.8µm reflectances cloud phase very similar LW angular modelling close, small difference in the “good direction” (increase of the limb-darkening). dust flag may differ in some semi-transparent situations AOD 2% higher at 0.6µm, 0.6% higher at 0.8 µm and 1.6% lower at 1.6 µm. Ratio of AOD does not correspond to ratio in reflectance.

30. Intercomparison of broadband quantities GERB-like BB radiances (NB->BB) –reflected solar –emitted thermal GERB-like BB fluxes (NB->BB + ADMs) –reflected solar –emitted thermal

31. GERB-like Reflected Solar Radiance

32. GERB-like Emitted Thermal Radiance

33. GERB-like Reflected Solar Flux ratio MSG2/MSG1

34. GERB-like Emitted Thermal Flux ratio MSG2/MSG1

35. Summary for the broadband products solar radiance MSG2/MSG1 = 1.012 thermal radiance MSG2/MSG1 = 0.9964 solar flux MSG2/MSG1 = 1.012 thermal flux MSG2/MSG1 = 0.9954

36. Conclusions and future work start of GERB-1 processing with SEVIRI on MSG2 good consistency with MSG1, most of the differences are explained by the level 1.5 SEVIRI data intercomparison, GERB-like radiances and fluxes are a bit closer to the actual GERB products To be done: analysis of the influence of the SEVIRI radiance definition (change from spectral radiance to effective radiance in April 2008).