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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. Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processing. MSG1 -> MSG2 transition. New GERB instrument but also new SEVIRI imager Are the SEVIRI scene identifications consistent?

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Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processing

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

  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=1.635µm MSG2s=1.635µm MSGs=0.809µm MSG2s=0.807µm

  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 0.6 VIS 0.8

  24. LW ADM due to the change in NB radiances F=p L / R(q,L6.2, L10.8, L12,L13.4) FMSG1'/FMSG1 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).

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