Inter-calibration of the SEVIRI VIS0.6 channel with MODIS Aqua, using Deep Convective Clouds as transfer targets Sébast

1. Aqua/MODIS 11m Inter-calibration of the SEVIRI VIS0.6 channel with MODIS Aqua, using Deep Convective Clouds as transfer targetsSébastien Wagner, Tim Hewison SEVIRI Met-9 DCC counts – 0.6 m MODIS Aqua DCC radiance – 0.6 m Met-9/SEVIRI 10.8m Shifted distributions! GOS GSICS Users SCOPE CM NWP centres Developers of Lev2/3 products ... Missing DCCS due to test on VZA Corrections Level 1b/c Data (Radiances) MODIS radiances Shift in the PDFs Shift in the PDFs + double peaking for 07/2008 Test on the view zenith angle CONTEXT: Past and current geostationary imagers: no on-board calibration for the Solar Reflective Bands.  Calibration exclusively based on vicarious approaches using various target types (e.g. deserts, clouds, oceans, Moon). Constellation of geostationary satellites do not see the same targets (in particular deserts and oceans)  Data sets harmonization and comparability are challenging. SCOPE: Comparability : achievable through the use of a common reference instrument on-board a polar satellite Which reference for Solar Reflective Bands? GSICS recommendation = MODIS/Aqua Which targets? In order to reduce uncertainties  inter-calibration over similar targets with well characterized radiative properties such as Deep Convective Clouds Which method? Implementation of the algorithm developed by Doelling et al. (2011), applied to the VIS0.6 channel, available on the Spinning Enhanced Visible and Infrared Imager (SEVIRI) aboard the Meteosat-8, - 9 and -10 satellites with MODIS-Aqua. Statement of Needs THE GOS BOX AT EUMETSAT FOR RSB: THE SEVIRI SOLAR CHANNEL CALIBRATION SYSTEM What was wrong??? 2008 1.2 % 2011 1.7 % RSB: Inter-calibration with MODIS using DCCs After ADM correction Before ADM correction -2.8% -5.7 % RSB: Inter-calibration with ROLO using the Moon • Developed and implemented in 2002/2003 (Govaerts et al. 2004) • System in place for SEVIRI (Met-8, Met-9 and Met 10) BUT ALSO for MVIRI (Met-2 till Met-7) • Vicarious calibration: • Reference = RTM simulations of Top-Of-Atmosphere radiances • Evaluated against well-calibrated polar-orbiting instruments • (SeaWiFs, ATSR2, AATSR, VEGETATION, MERIS) • Comparison with TOA measured signal • 2 target types used for comparison: • Desert bright targets (18 targets) • Dark sea targets (9 targets) (checking purposes) 2010 Absolute calibration 2012 2009 MODIS Aqua (01/04/2010 – 13:00) SEVIRI Met-9 (01/04/2010 – 12:57) Derived gain for Julys • USE OF DEEP CONVECTIVE CLOUDS AS CALIBRATION TARGETS • TWO-FOLD APPROACH: • Implementation of an inter-calibration algorithm based on the use of DCCs for VIS06 • Development of a vicarious calibration algorithm to be added to the current SSCC system (absolute calibration + drift monitoring) PROVIDING CORRECTIONS TO ENSURE COMPARIBILITY AND HOMOGENEITY: THE GSICS BOX : INTERCALIBRATION WITH MODIS/Aqua USING DEEP CONVECTIVE CLOUDS GOS = Global observing System RSB = Reflective solar bands • Satellite : MET-9 (0.0 Lat / 0.0 Lon) • Band : VIS 06 Main steps of the method as in Doelling et al, 2011 • 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 and SEVIRI 10.8 m (BT<205K) • Spatial homogeneity (over boxes of pixels in the “11 m” BT + in the “0.6 m” radiances) • 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) • Construction of the Probability Density Functions on a monthly basis • Derivation of the gain from the calibration equation: Example of DCCs tracking with MODIS and SEVIRI as implemented Preliminary results for a few cases... as shown in September 2012 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 reasons? NEW RESULTS AFTER LATEST DEVELOPMENTS... STILL NOT SATISFYING! LATEST DEVELOPMENTS • MODIS reference radiance derived from a PDF covering 07/2002 – 02/2003 • MET-9 PDF built independently • Still large variability in the gain time series • Potential seasonal cycle (even though more gains should be derived over a longer period) • Problem seems to be with the ADM correction (introduces a shift in the radiance and count distributions) •  Implementation of the ADM to be revisited CONCLUSIONS • Implementation of the GSICS ATBD still on-going: • Requires further checks and debugging as some issues still to be solved (in particular implementation of the Angular Distribution Model) • Uncertainty analysis still missing • Limited to the MET-09/SEVIRI VIS06 band • FUTURE WORK: • Validation against D. Doelling results (by the end of June) • Generation of a GSICS product (demonstration dataset) for MET-9 (end 2013 – early 2014) • Generation of validation datasets for GSICS community • Integration of the algorithm in the monitoring processing chain (MET-8, 9 and 10) • Reprocessing of the past data: • MFGs (in particular MET-7) • 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) COMPARISONS OF THE PDFS BEFORE AND AFTER ADM CORRECTIONS Govaerts, Y. M. and M. Clerici (2004). "Evaluation of radiative transfer simulations over bright desert calibration sites." IEEE TGRS 42(1): 176-187. Govaerts, Y. M., M. Clerici, Clerbaux N. (2004). "Operational Calibration of the Meteosat Radiometer VIS Band." IEEE TGRS 42(9): 1900-1914. Govaerts, Y. M., and Clerici, M. (2004). “MSG-1/SEVIRI Solar Channels Calibration Commissioning Activity Report” (EUMETSAT). Doelling D. et al. (2011), “ATBD for Deep Convective Cloud technique of calibrating GEO sensors with Aqua-MODIS for GSICS”, https://gsics.nesdis.noaa.gov/pub/Development/AtbdCentral/GSICS_ATBD_DCC_NASA_2011_09.pdf. 1: EUMETSAT, Eumetsat-Allee 1, D-64295 Darmstadt, Germany Please send questions and comments to sebastien.wagner@eumetsat.int NOAA Satellite Conference, College Park, MD, USA, 8-12 April 2013