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GERB fluxes – Method for Regional V alidation

GERB fluxes – Method for Regional V alidation. Nicolas Clerbaux and RMIB GERB team Royal Meteorological Institute of Belgium GIST 21 – Boulder – April 2 2004. Content. Brief summary of the GERB radiance-to-flux conversions Shortwave Longwave Regional Validation Method Data

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GERB fluxes – Method for Regional V alidation

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  1. GERB fluxes – Method for Regional Validation Nicolas Clerbaux and RMIB GERB team Royal Meteorological Institute of Belgium GIST 21 – Boulder – April 2 2004

  2. Content • Brief summary of the GERB radiance-to-flux conversions • Shortwave • Longwave • Regional Validation • Method • Data • Illustrations • Additional things to do • Conclusions

  3. GERB Shortwave flux • CERES TRMM SW ADM selection based on the RMIB-SEVIRI scene identification. Note: • No aerosol information • No snow ADM • No wind speed over ocean information • CERES TRMM SW ADM application: • No interpolation in term of cloud properties (fraction, optical depth and phase): use the bin value • Tri-linear interpolation in term of angles • Weighting in case of mixed surface types:

  4. Shortwave Angular Dependency Models Use of the 592 CERES-TRMM SW ADMs:

  5. GERB Longwave Flux • Regression in terms of SEVIRI (imager) NB thermal radiances • Parameterisation using the SBDART radiative transfer model

  6. Longwave Anisotropic Factor R

  7. GERB Radiance-to-flux Validation • Needed before data release (date TBD), input for Quality Summary • Validation of TRMM ADM applied on GEO data by Norman Loeb: performed on CERES-TRMM data for 1998/2000 (no SEVIRI scene id.!) • GERB always observes a region from the same direction-> need of a regional validation • Should be performed for different (all) positions of the sun in the sky • Method: similar to the Direct Integration test but with angular sampling provides by CERES in RAPS mode -> need a preliminary regional comparison of the unfiltered radiances

  8. Method • CERES in RAPS mode for a given time period (some months) • Collocated GERB measurements (GERB is continuous in space and time) • Direct Integration of the CERES data in regional box provides the averaged “true flux” : <FDI>= int {cos qv sin qv <Lceres(qv,f)>} or <FDI>= <Fceres> • Comparison with the corresponding GERB mean flux in the box: <Fgerb > • Regional analysis of the Difference/Ratio at 10:30 LT (Terra) and 1:30 LT (Aqua)

  9. Data • GERB: • Processed with SEVIRI since 19 Dec. 2003 • Validation period Dec 2003 -> June 2004 • Some scene id. problems fixed March 2004 • CERES: • FM2 (Terra) and FM3 (Aqua) for RAPS mode • ES8 Edition 1, ES8 Edition 2, SSF

  10. Illustrations of the method using ES8 Ed. 1 data for 19/12/2003 -> 31/02/2004 Terra FM2 coverage (52 days) Aqua FM3 coverage (23days)

  11. Ratio LW – GERB-2/CERES FM3 (day and night) – 4*4 ARG pixels Mean GERB Mean CERES

  12. Ratio LW – GERB-2/CERES FM2 (night only) – 4*4 ARG pixels

  13. Ratio SW – GERB-2/CERES FM2 – 4*4 ARG pixels

  14. Shortwave (2) – GERB-2/CERES FM3 – 4*4 ARG pixels

  15. Additional things to do • Analysis of spatial/angular/temporal sampling • Regional analysis of unfiltered radiances • Switch to ES8 Edition 2 and SSF when available • Regional analysis of difference when the true flux <Fceres> is provided by the ES8 files or by the SSF (one month in 2002?).

  16. Conclusions • Regional validation of the GERB fluxes will be performed. • Based on CERES RAPS data -> only 4 local time. • Need additional analysis in term of radiance for a correct interpretation of the results. • First results expected for this summer.

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