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RMIB GERB Processing : overview and status

This document provides an overview of the GERB processing system, covering physical fundamentals, methodology, subsystem division, status updates, and future plans. It includes details on measurements, thermal/solar radiance separation, flux estimation, interface schemes, input data, unfiltering methods, geolocation, resolution enhancement, and software status.

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RMIB GERB Processing : overview and status

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  1. RMIB GERB Processing: overview and status S. Dewitte Royal Meteorological Institute of Belgium GIST, Boulder, 31/03/2004

  2. Overview • 1. Physical fundamentals • 2. External interfaces • 3. Methodology • 4. Internal division into subsystems • 5. Status GIST, Boulder, 31/03/2004

  3. GERB measurements • General measurement: filtered radiance Lf • total (TOT) filtered radiance : 0.3-50 micron • short wave (SW) filtered radiance : 0.3-4 micron GIST, Boulder, 31/03/2004

  4. Thermal/solar radiance separation • LfSW = reflected solar radiation • synthetic long wave (LW) radiance LfLW =LfTOT -A LfSW • A is chosen such that for reference SW spectrumLfLW = emitted thermal radiation GIST, Boulder, 31/03/2004

  5. Removal of non flat spectral response effects • Lf = measured radiance, filtered with spectral response instrument • Luf = wanted radiance, not filtered with spectral response instrument • unfilter factor Luf/Lf must be estimated from spectral modelling • scene type dependent GIST, Boulder, 31/03/2004

  6. Flux estimation • F = wanted flux = integral of unfiltered radiance contributions from all directions of the upper hemisphere • angular conversion factor F/ Luf must be estimated from modelling of the angular distribution of the observed radiation • scene type dependent GIST, Boulder, 31/03/2004

  7. Interface scheme Interfaces to : • RAL = Rutherford Appleton laboratories • EUMETSAT = European METeorological SATellite exploitation • Users GIST, Boulder, 31/03/2004

  8. GERB input data • NANRG: Non Averaged Non Rectified Geolocated GERB filtered radiances • one pair of SW and TOT filtered radiances every 5 minutes • nominal resolution 50 km at nadir (PSF weighted) GIST, Boulder, 31/03/2004

  9. SEVIRI input data • (HRV), 0.6, 0.8, 1.6 micron: solar band channels • (3.8 micron: intermediate) • 6.2, 7.3, 8.7, 9.7, 10.8, 12, 13.4 micron: thermal channels • all used channels at resolution of 3 km at nadir GIST, Boulder, 31/03/2004

  10. Unfiltering and angular conversion methodology GERB derived spectral correction factor for SEVIRI based flux estimate SEVIRI derived unfilter factor for GERB measurement SEVIRI derived unfilter and angular conversion factor for GERB measurement GIST, Boulder, 31/03/2004

  11. Thermal/solar separation methodology • contributions to filtered radiance estimated separately from SEVIRI • main quantities: LfSW,sol,SEVIRI LfLW,th,SEVIRI • small quantities: LfSW,th,SEVIRI LfLW,sol,SEVIRI • sum contributionsLfSW,SEVIRI = LfSW,sol,SEVIRI + LfSW,th,SEVIRILfLW,SEVIRI = LfLW,th,SEVIRI + LfLW,sol,SEVIRI GIST, Boulder, 31/03/2004

  12. Internal division into subsystems GIST, Boulder, 31/03/2004

  13. SEVIRI Processing • estimates filtered radiances at SEVIRI pixel level • estimates unfiltered radiances at SEVIRI pixel level • estimates fluxes at 3 x 3 SEVIRI pixel level • Uses CERES TRMM ADM for SW case. • Scene identification from SEVIRI • concentrates all the needed physical scene modelling from SEVIRI data GIST, Boulder, 31/03/2004

  14. GERB Processing • convolution of SEVIRI based filtered radiance estimates over GERB footprint • time interpolation from SEVIRI acquisition times to GERB acquisition times • flux estimation at GERB footprint level • temporal averaging of 3 5’ fluxes to 15’ flux • concentrates GERB-SEVIRI coregistration GIST, Boulder, 31/03/2004

  15. Geolocation • Nominal: use GGSPS geolocation derived from SEVIRI parameters (version 1) • Target accuracy: SEVIRI pixel • Currently used: match GERB to SEVIRI (version 2) • Accuracy: order half GERB pixel GIST, Boulder, 31/03/2004

  16. Resolution enhancement • From the flux estimation at low resolution (GERB footprint), compatible fluxes at higher resolution (3 x 3 SEVIRI pixels) are calculated. • The compatible fluxes are corrected SEVIRI based flux estimates. • The same correction factors can be applied to the SEVIRI based unfiltered radiance estimates. • concentrates resolution enhancement of GERB by SEVIRI GIST, Boulder, 31/03/2004

  17. Status -software • Full system running since 19/12/2003: • Geolocation based on matching (version 2) • SEVIRI as imager (G2/SEV1) • Cloud problem (sunglint/Sahel) solved since begin March GIST, Boulder, 31/03/2004

  18. In progress • Validation of unfiltered radiances • New LOS non-repeatability error correction: implemented and tested, not yet activated • Validation of Fluxes • Validation of Cloud cover and optical depth GIST, Boulder, 31/03/2004

  19. Future • Validation of Cloud phase • Reprocessing GIST, Boulder, 31/03/2004

  20. Conclusions • RGP produces GERB unfiltered radiances and fluxes in near real time. • SEVIRI used as auxiliary data for • Spectral unfiltering • Scene id for ADM selection • Resolution enhancement • Near nominal processing since 19/12/2003. • Validation: in progress. GIST, Boulder, 31/03/2004

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