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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"
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2 Introduction Introduction Validation for the CloudNet sites Sensitivity Norrkoping Cloud Work Shop results Conclusions
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3 Introduction
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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: 0 -256 Water clouds: spherical droplets (1 -24 m) Ice clouds: imperfect hexagonal crystals (6,12, 26, 51 m)
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5 Examples Meteosat-8 Cloud Properties Cloud Thermodynamic Phase Water Ice Clear Cloud Optical Thickness
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6 Inter-calibration NOAA-17/AVHRR & METEOSAT-8/SEVIRI
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7 Inter-Calibration: NOAA17 vs. METEOSAT-8 Diff. ~5%Diff. ~20% SEVIRI vs. AVHRR reflectances using observations from August – December 2004 over Central Africa.
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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%
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9 Validation
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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
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11 Comparison: Example CLWP product SEVIRI CLWP 1 May 2004CLWP time series from SEVIRI and microwave radiometer at Chilbolton, UK
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12 CLWP Validation Distribution of diff. LWP Meteosat-8 - MW, July 2004 (Chilbolton) Distribution of Meteosat-8 LWP July 2004 (Chilbolton)
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13 CLWP Validation: Daily medians summer Chilbolton, UK
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14 CLWP Validation: Monthly medians summer Chilbolton, UK Palaiseau, France
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15 CLWP Validation: Daily medians one year Chilbolton, UK
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16 CLWP Validation: Monthly medians one year Chilbolton, UK
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17 Validation Pyranometer
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18 Sensitivity
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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 )
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20 Assessment error budget RTRT & FOV FOV Total
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21 Assessment error budget
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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
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23 Sensitivity: viewing geometry Loeb and Coakley, 1997, Journal of Climate
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24 Conclusions
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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
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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.
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27 Comparison Cloud Work Shop 17 January 2006
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28 Comparison CWS: Cloud Optical Thickness
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29 Comparison CWS: Effective Radius
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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
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32 Inter-calibration NOAA-17/AVHRR & METEOSAT-8/SEVIRI
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33 Inter-Calibration: NOAA17 vs. METEOSAT-8 Diff. ~5%Diff. ~20% SEVIRI vs. AVHRR reflectances using observations from August – December 2004 over Central Africa.
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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%
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35 Sensitivity: viewing geometry Fig. 0.6 m reflectance vs. viewing zenith angle AVHRRMSGAVHRRMSG
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36 Sensitivity: viewing geometry Fig. 1.6 m reflectance vs. viewing zenith angle AVHRRMSG AVHRRMSG
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37 Retrieval Method Water Clou ds Ice Clou ds
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38 Influence of reflectance spectra SCIAMACHY reflectance spectra for 5 typical scenes (Stammes et al. 2005) Diff. Ice clouds < 10%Diff. Water cloud < 3%
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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
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40 CLWP Validation: Palaiseau daily results
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41 Sensitivity: retrieval cloud optical thickness Fig. 0.63 m reflectivities Error in retrieved COT and Reff assuming errors of ± 1, 2 and 3% Fig. 1.6 m reflectivities
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42 Results using pre-launch calibration Cum. freq. dist. COT for water clouds Cum. freq. dist. CLWP for water clouds SEVIRI > AVHRR Diff. 0- 20%Diff. 10 - 20% SEVIRI < AVHRR
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43 Position station
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