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Rob Roebeling, Hartwig Deneke and Arnout Feijt

Rob Roebeling, Hartwig Deneke and Arnout Feijt. GEWEX Cloud Assessment Meeting Madison, United States of America 6 -7 July 2006 "METEOSAT-8 (SEVIRI) CLOUD PROPERTY RETRIEVALS FOR CLIMATE STUDIES". Introduction. Introduction Validation for the CloudNet sites Sensitivity

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Rob Roebeling, Hartwig Deneke and Arnout Feijt

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  1. Rob Roebeling,Hartwig Deneke and Arnout Feijt GEWEX Cloud Assessment Meeting Madison, United States of America 6 -7 July 2006 "METEOSAT-8 (SEVIRI) CLOUD PROPERTY RETRIEVALS FOR CLIMATE STUDIES"

  2. Introduction • Introduction • Validation for the CloudNet sites • Sensitivity • Norrkoping Cloud Work Shop results • Conclusions

  3. Introduction

  4. Retrieval Method • Project: Climate Monitoring SAF (CM-SAF) • Satellites: METEOSAT-8/SEVIRI and NOAA-17/AVHRR • Channels: VIS(0.63 mm) and NIR(1.6 mm) and IR (10.8 mm) • Products: COT, CLWP, CPH (and Reff) • RTM: Doubling Adding KNMI model (DAK) • Surface reflectance: MODIS white sky albedo • Optical thicknesses: 0 -256 • Water clouds: spherical droplets (1 -24 mm) • Ice clouds: imperfect hexagonal crystals (6,12, 26, 51 mm)

  5. Cloud Thermodynamic Phase Water Ice Clear Cloud Optical Thickness Examples Meteosat-8 Cloud Properties

  6. Inter-calibration NOAA-17/AVHRR & METEOSAT-8/SEVIRI

  7. Diff. ~5% Diff. ~20% Inter-Calibration: NOAA17 vs. METEOSAT-8 SEVIRI vs. AVHRR reflectances using observations from August – December 2004 over Central Africa.

  8. Diff. 0- 5% Diff. 0- 5% Results after re-calibration SEVIRI and AVHRR COT and CLWP after re-calibration to MODISusing observations of April and May 2004 over Northern Europe. (SEVIRI: 0.6 mm + 6% and 1.6 mm +2%; AVHRR: 0.6 mm + 6% and 1.6 mm +22%)

  9. Validation

  10. Cabauw Chilbolton Chilbolton Paris CloudNet Data CLWP: 1 year of microwave radiometer data at 2 CLOUDNET sites COT: 1 year of pyranometer data, 27 stations

  11. Comparison: Example CLWP product SEVIRI CLWP 1 May 2004 CLWP time series from SEVIRI and microwave radiometer at Chilbolton, UK

  12. CLWP Validation Distribution of Meteosat-8 LWP July 2004 (Chilbolton) Distribution of diff. LWP Meteosat-8 - MW, July 2004 (Chilbolton)

  13. CLWP Validation: Daily medians summer Chilbolton, UK

  14. CLWP Validation: Monthly medians summer Chilbolton, UK Palaiseau, France

  15. CLWP Validation: Daily medians one year Chilbolton, UK

  16. CLWP Validation: Monthly medians one year Chilbolton, UK

  17. Validation Pyranometer

  18. Sensitivity

  19. Assessment error budget • Co-location & resolution (48 g m-2) • Position ground station • Parallax • VIS – NIR mismatch • Wobbling of the satellite • Plane parallel assumption • MW – Radiometer (30 g. m-2) • Difference due to sampling different cloud portions (20 g m-2)

  20. Assessment error budget RT RT & FOV FOV FOV FOV Total

  21. Assessment error budget

  22. Sensitivity: viewing geometry 6:00hr 0 = 70  = 83 7:00 hr 0 = 60  = 97 8:00 hr 0 = 51  = 110 9:00 hr 0 = 42  = 123 Fig. CLWP frequency distributions 21 June 2006 over Northern Europe

  23. Sensitivity: viewing geometry Loeb and Coakley, 1997, Journal of Climate

  24. Conclusions

  25. Conclusions (1) • Re-calibration reduces the differences between NOAA-17 and METEOSAT-8 retrievals of COT and CLWP over Northern-Europe to about 5%. • There is good agreement between SEVIRI and microwave radiometer retrieved cloud liquid water path. • The accuracy of SEVIRI CLWP retrievals decreases at solar zenith angles > 60 degrees. • Accuracy changes due to geometry may manifest artificial trends

  26. Conclusions (2) • Part of the validation differences can be explain by co-location and sampling differences. • The 15 minutes time resolution SEVIRI have enabled the synergetic use of ground-based and satellite observations.

  27. Comparison Cloud Work Shop 17 January 2006

  28. Comparison CWS: Cloud Optical Thickness

  29. Comparison CWS: Effective Radius

  30. Reflectance,  q0 q tac Above the cloud Scattering and absorption f tbc Below the cloud R(sur) Methods: Radiative Transfer Modelling Cloud properties • Geometric thickness • Thermodynamic phase • Optical thickness • Effective radius • Droplet distribution

  31. Inter-calibration NOAA-17/AVHRR & METEOSAT-8/SEVIRI

  32. Diff. ~5% Diff. ~20% Inter-Calibration: NOAA17 vs. METEOSAT-8 SEVIRI vs. AVHRR reflectances using observations from August – December 2004 over Central Africa.

  33. Diff. 0- 5% Diff. 0- 5% Results after re-calibration SEVIRI and AVHRR COT and CLWP after re-calibration to MODISusing observations of April and May 2004 over Northern Europe. (SEVIRI: 0.6 mm + 6% and 1.6 mm +2%; AVHRR: 0.6 mm + 6% and 1.6 mm +22%)

  34. AVHRR AVHRR MSG MSG Sensitivity: viewing geometry Fig. 0.6 mm reflectance vs. viewing zenith angle

  35. AVHRR AVHRR MSG MSG Sensitivity: viewing geometry Fig. 1.6 mm reflectance vs. viewing zenith angle

  36. Retrieval Method Water Clouds Ice Clouds

  37. Influence of reflectance spectra SCIAMACHY reflectance spectra for 5 typical scenes (Stammes et al. 2005) Diff. Water cloud < 3% Diff. Ice clouds < 10%

  38. COT NOAA-AVHRR, May 2004 COT Meteosat-8, May 2004 CLWP NOAA-AVHRR, May 2004 CLWP Meteosat-8, May 2004 Monthly COT and CLWP composites

  39. CLWP Validation: Palaiseau daily results

  40. Sensitivity: retrieval cloud optical thickness Error in retrieved COT and Reff assuming errors of ± 1, 2 and 3% Fig. 0.63 mm reflectivities Fig.1.6 mm reflectivities

  41. Diff. 0- 20% Diff. 10 - 20% Results using pre-launch calibration SEVIRI > AVHRR SEVIRI < AVHRR Cum. freq. dist. COT for water clouds Cum. freq. dist. CLWP for water clouds

  42. Position station

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