Inter-calibration of the SEVIRI VIS 06 band against MODIS Aqua, using Deep Convective Clouds as transfer targets Sébastien Wagner, Tim Hewison In collaboration with D. Doelling (NASA) Contact: sebastien. wagner@eumetsat. int GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Outline 1. GSICS activities for solar reflective bands at EUMETSAT 2. Current calibration system (for the solar reflective bands) 3. Inter-calibration with MODIS using DCCs a) Main steps b) Some results 4. Conclusions and future work GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Outline 1. GSICS activities for solar reflective bands at EUMETSAT 2. Current calibration system (for the solar reflective bands) 3. Inter-calibration with MODIS using DCCs a) Main steps b) Some results 4. Conclusions and future work GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
GSICS current activities for solar reflective bands at EUMETSAT SCOPE CM Level 1 b/c Data (Radiances) Corrections NWP centres Developers of Lev 2/3 products. . . GOS Users GSICS Statement of Needs Inter-calibration with MODIS using DCCs Absolute calibration Inter-calibration with ROLO using the Moon To be discussed !!! GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
GSICS current activities for solar reflective bands at EUMETSAT The GOS box: Absolute calibration using the SEVIRI Solar Channel system Positive feedback 1. MVIRI/VIS band 2. SEVIRI/ VNIR bands + HRVIS 3. Prepare MTG/FCI No GSICS product but increased understanding of the calibration system thanks to Act. 1 and Act. 2 The GSICS box: 1. Inter-calibration with MODIS using DCCs 1. 2. 2. MET-9 VIS 06 MET-8 and 10 VIS 06 + MVIRI GSICS dataset for validation purposes + GSICS product generation planned (demonstration dataset) Inter-calibration with ROLO using the Moon 1. All SEVIRIs (currently MET-8, 9 and 10) for all VIS/NIR bands (VIS 06 / VIS 08 / NIR 16 / HRVIS) GSICS dataset for validation purposes + potential product (demo dataset) 2. Feasibility study for MVIRI (Meteosat First Generation) for the VIS band 3. Future programs (MTG/FCI + EPS-SG/MET Image) GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Outline 1. GSICS activities for solar reflective bands at EUMETSAT 2. Current calibration system (for the solar reflective bands) 3. Inter-calibration with MODIS using DCCs a) Main steps b) Some results 4. Conclusions and future work GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
What about the SEVIRI solar band calibration (GOS box)? • 4 solar channels ( VIS 06 / VIS 08 / NIR 16 / HRVIS ) • Specifications for the solar channel calibration? SEVIRI = 10% accuracy + 2% of the maximum dynamic range for long-term stability Achieved by vicarious calibration SEVIRI Solar Channel Calibration syst. (Govaerts et al. , TGRS 2004) • Reference = RTM simulations of Top-Of-Atmosphere radiances (evaluated against wellcalibrated polar-orbiting instruments) • Comparison with TOA measured signal above desert and ocean targets • Currently: Meteosat 8: launch = 28/08/2002 operation = 19/01/2004 Meteosat 9: launch = 21/12/2005 operation = 18/07/2006 Meteosat 10: launch = 05/07/2012 operation = 21/01/2013 VIS 06 HRVIS Slide : 7 NIR 16 VIS 08 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Outline 1. GSICS activities for solar reflective bands at EUMETSAT 2. Current calibration system (for the solar reflective bands) 3. Inter-calibration with MODIS using DCCs a) Main steps b) Some results 4. Conclusions and future work GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Inter-calibration of SEVIRI with Aqua/MODIS using DCCs • Starting point: • ATBD as provided by D. Doelling et al. , 2011 (https: //gsics. nesdis. noaa. gov/wiki/Home) • Use of MODIS Aqua as a reference • Within EUMETSAT, two-fold approach: 1. Implementation of an inter-calibration algorithm based on the use of DCCs for VIS 06 GSICS box 2. Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring) GOS box • Satellite: MET-9 (0. 0 Lat / 0. 0 Lon) • Band: VIS 06 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Main steps of the method as in Doelling et al, 2011 1. DCC identification • Time: for MET-9 (0. 0 Lat / 0. 0 Lon) 11: 00 < t < 14: 00 • Geometry: • Lat / Lon between 0. 0 and +/- 20. 0 degrees (with respect to the SSP) • SZA and VZA < 40 degrees • DCC identification threshold using the MODIS 11 m band SEVIRI 10. 8 m (BT<205 K) • Spatial homogeneity (over boxes of pixels in the “ 11 m” BT + in the “ 0. 6 m” radiances) 2. Conversion from counts to overhead sun + spectral transformation to account for Spectral Response Function differences between MODIS and SEVIRI • Use of an Angular Distribution Model (Hu model, Hu et al. 2004) • Use of correction factors as given by the GSICS ATBD (Doelling et al, 2011) 3. Construction of the Probability Density Functions on a monthly basis 4. Derivation of the gain from the calibration equation: Slide : 10 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Example of DCCs tracking with MODIS and SEVIRI as implemented Aqua/MODIS 11 m Met-9/SEVIRI 10. 8 m Test on the view zenith angle Missing DCCS due to test on VZA MODIS Aqua (01/04/2010 – 13: 00) Slide : 11 SEVIRI Met-9 (01/04/2010 – 12: 57) GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Preliminary results for a few cases. . . as shown in September 2012 SEVIRI Met-9 DCC counts – 0. 6 m MODIS Aqua DCC radiance – 0. 6 m Shift in the PDFs + double peaking for 07/2008 0. 57 2008 2011 1. 2 % 0. 56 0. 55 0. 54 0. 53 Slide : 12 0. 52 -2. 8% 1. 7 % 2010 2009 -5. 7 % 2012 Derived gain for Julys. Annual Meeting – Williamsburg (VA), 4 -8 March 2013 GSICS 0. 51 What is wrong? ? ?
Possible reasons for bad results and solutions. . . • Standard uncertainty u / mean < 0. 2% with Sampling problem but not only. . . • MODIS PDF derived dynamically (in parallel with SEVIRI PDF) wrong! MODIS PDF to be derived for a time interval in early years of operations • Implementation of the ADM correction • Angle calculation • Correction calculation • Other? Latest changes in the algorithm: MODIS reference radiance derived from a PDF covering 07/2002 – 02/2003 MET-9 PDF built independently GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
New results. . . just the Julys Significant improvement! At least apparently. . . GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
New results. . . GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Comparisons of the PDFs before and after ADM corrections Shifted distributions! MODIS radiances Before ADM correction After ADM correction GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Comparisons of the PDFs before and after ADM corrections Count PDFs after ADM correction PDFs for the original counts MET-09/SEVIRI counts GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Outline 1. GSICS activities for solar reflective bands at EUMETSAT 2. Current calibration system (for the solar reflective bands) 3. Inter-calibration with MODIS using DCCs a) Main steps b) Some results 4. Conclusions and future work GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Conclusions • Implementation of the GSICS ATBD still on-going: • Requires further checks and debugging as some issues still to be solved • Uncertainty analysis still missing • Limited to the MET-09/SEVIRI VIS 06 band • Future work: Ø Validation against D. Doelling results Ø Generation of a GSICS product (demo) for MET-9 Ø Generation of validation datasets for GSICS community Ø Integration of the algorithm in the monitoring processing chain (MET-8, 9 and 10) Ø Reprocessing of the past data: v MFGs (in particular MET-7) v MSGs (MET-8 and 9) • Once problems are solved Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring) Slide : 19 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Thank you Slide : 20 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Back-up slides for general purposes Slide : 21 GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
Context. . . GSICS • What is GSICS? – Initiative of CGMS and WMO – Effort to produce consistent, well-calibrated data from the international constellation of Earth Observing satellites • What are the basic strategies of GSICS? – Improve on-orbit calibration by developing an integrated inter-calibration system (GEO-LEO, LEO-LEO) – Best practices for prelaunch characterisation (with CEOS WGCV) • Benefits: – – – Improve consistency between instruments Reduce bias in Level 1 and 2 products Provide traceability of measurements Retrospectively re-calibrate archive data Better specify future instruments Slide : 22 EUMETSAT CNES JMA NOAA CMA KMA ISRO NASA WMO USGS NIST JAXA IMD ESA GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013 ROSHYDROMET
Context. . . GSICS principles • Systematic generation of inter-calibration products • For Level 1 data from passive satellite sensors (weather, climate and other environmental applications) • To compare, monitor and correct the calibration of monitored instruments to community references • By generating calibration corrections (NRT / Re-analysis applications) with specified uncertainties • Through well-documented, peer-reviewed procedures • Based on various techniques to ensure consistent and robust results • Delivery to users • Free and open access • Adopting community standards • To promote • Greater understanding of instruments’ absolute calibration • More accurate and more globally consistent retrievals • Inter-operability for more accurate environmental, climate and weather forecasting products GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013 TRACEABILITY / UNBROKEN CHAINS OF COMPARISONS
Using Deep Convective Clouds as transfer target for inter-calibration of SEVIRI with Aqua/MODIS • DCCs = invariant targets • Available all around the Earth (not the case for desert for example) seen by all GEO satellites • Well characterized and easily detectable (infra-red threshold) • Higher part of the dynamic range • Seen by well calibrated instruments on board polar satellites calibration transfer targets Þ Outcome: 1. Improved calibration and long term monitoring of the instruments 2. Consistent calibration across the GEO satellite constellation • Within the GSICS framework: • ATBD as provided by D. Doelling et al. , 2011 (https: //gsics. nesdis. noaa. gov/wiki/Home) • Use of MODIS Aqua as a reference • Within EUMETSAT, two-fold approach: 1. Implementation of an inter-calibration algorithm based on the use of DCCs for VIS 06 2. Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring) GSICS Annual Meeting – Williamsburg (VA), 4 -8 March 2013
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