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  m) and NIR (1.6  m) and IR (10.8  m)  Products: COT, CLWP, CPH (and R eff )  RTM: Doubling Adding KNMI model (DAK) Surface reflectance: MODIS white sky albedo Optical thicknesses: Water clouds: spherical droplets (1 -24  m) Ice clouds: imperfect hexagonal crystals (6,12, 26, 51  m)

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

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

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

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

9 Validation

10 CloudNet Data Cabauw Paris Chilbolton  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 2004CLWP time series from SEVIRI and microwave radiometer at Chilbolton, UK

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

31 Methods: Radiative Transfer Modelling R(sur) Above the cloud Below the cloud  ac  bc Scattering and absorption Reflectance,    Cloud properties Geometric thickness Thermodynamic phase Optical thickness Effective radius Droplet distribution Cloud properties Geometric thickness Thermodynamic phase Optical thickness Effective radius Droplet distribution

32 Inter-calibration NOAA-17/AVHRR & METEOSAT-8/SEVIRI

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

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

35 Sensitivity: viewing geometry Fig. 0.6  m reflectance vs. viewing zenith angle AVHRRMSGAVHRRMSG

36 Sensitivity: viewing geometry Fig. 1.6  m reflectance vs. viewing zenith angle AVHRRMSG AVHRRMSG

37 Retrieval Method Water Clou ds Ice Clou ds

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

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

40 CLWP Validation: Palaiseau daily results

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

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

43 Position station