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C édric Bertrand

GERB SW fluxes: an update (Clear ocean SW radiances and fluxes in the reprocessed V999 June 04 data). C édric Bertrand. GIST 24 14-16 th December, Imperial College, London, U.K. RECAP: unfiltering. New spectral response function New spectral conversion:. V002.  = unfilter factor. where:.

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C édric Bertrand

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  1. GERB SW fluxes: an update(Clear ocean SW radiances and fluxes in the reprocessed V999 June 04 data) Cédric Bertrand GIST 24 14-16th December, Imperial College, London, U.K.

  2. RECAP: unfiltering New spectral response function New spectral conversion: V002  = unfilter factor where: • = wavelength (m) I= reflected solar radiance (Wm-2.Sr-1.m-1) S=spectral response function (0 S 1) LSEVIRI = a + b1L0.6 + b2L0.8 + b3 L1.6 + c11L20.6 + c21 L0.8L0.6 + c22 L20.8 + c31 L1.6L 0.6 + c32 L1.6 L 0.8 + c33 L21.6 !!!! fct of SZA ONLY !!!!

  3. RECAP: unfiltering V999: Database of co-angular CERES and SEVIRI measurements (March, April and July 04 FM2/FM3 ES8 Edition 2 CERES data) LSEVIRIUF (LCERESUF = a + b L0.6 + c L0.8 + d L1.6 + eSZA sza 60°) with a, b, c, d and e surface types dependent LSEVIRIF CAN NOT BE DETERMINED FROM CERES DATA General case: LSEVIRIF = a’ + b’ L0.6 + c’ L0.8 + d’ L1.6 + e’SZA Clear Ocean: LSEVIRIF = LSEVIRIUF/SBDART (a", b" and c" = f(SZA,VZA,RAA))

  4. RECAP: angular conversion Radm = clear ocean wind speed dependent CERES-TRMM BB ADM anisotropic correction factor If  (glint angle) < 25°

  5. F l.n – F l.n-2:00(W.m-2) ARG JUNE 04 FADM FF FDUF FUF F l.n – F l.n+2:00(W.m-2) FADM FF FDUF FUF

  6. F l.n – F l.n-2:00(W.m-2) 3x3 SEVIRI JUNE 04 FADM FS3 FG3 F l.n – F l.n+2:00 (W.m-2) FADM FS3 FG3

  7. RECAP: resolution enhancement (I) Up-sampling of the filtered GERB radiances from the nominal GERB footprint resolution (i, j) to the 3 x 3 SEVIRI pixels resolution (x, y). BUT: rather than LfGERB we use CF = LfGERB/LfSEVIRI FIRST: Fluxes at the GERB footprint resolution (i, j) are derived from the 3 x 3 SEVIRI pixels (x, y) based flux estimates FGERB(i, j) = (xy PSF(i, j, x, y) . FS3(x, y)). CFL(i, j) CFL(i, j) = correction of SEVIRI by GERB SECOND: improvement of the spatial resolution of GERB fluxes by use of SEVIRI high resolution information FGERB(i, j) = xy PSF(i, j, x, y) . CFH(x, y) . FS3(x, y)

  8. RECAP: resolution enhancement (II) FINALLY: GERB flux at the 3 x 3 SEVIRI pixels resolution is given by FG3(x, y) = CFH(x, y) . FS3(x, y) To reduce the impact of the SEVIRI spectral conversion in the estimation of the GERB SW fluxes at the 3x3 SEVIRI pixels resolution: use of LfADM(x,y) rather than LfSEVIRI(x,y) in the CFL(i,j) computation. Limitation: while SBDART is a function of the 3 acquisition angles (sza, vza, and raa) it is still dependent of the assumed GERB spectral response function

  9. F l.n – F l.n-2:00(W.m-2) 3x3 SEVIRI JUNE 04 FS3 FG3 FG3_ADM_L F l.n – F l.n+2:00 (W.m-2) FS3 FG3 FG3_ADM_L

  10. UNFILTERED RADIANCE RATIO 05.06.04 LS3/LADM LG3/LADM LG3_ADM_L/LADM SZA VZA RAA -180 -90

  11. FLUX RATIO 05.06.04 FS3/FADM FG3/FADM FG3_ADM_L/FADM SZA VZA RAA -180 -90

  12. ARG: 05-06-04 FUF/FADM LUF/LADM

  13. Resolution enhancement limitations: GERB and SEVIRI images recorded at  times  temporal matching needed Scene types independent 100% clear GERB pixel 3x3 SEVIRI pixels footprint 100% cloudy Clear ocean S3 footprint for which the CFH(x,y) will be cloud contaminated

  14. Conclusions • Problems over clear land surfaces which were not found in the V002 version • Asymmetry problem in the diurnal evolution of the SW fluxes over clear ocean surface still present. • mainly due to deficiencies in the SEVIRI spectral modeling • but also possible impact of the - GERB spectral response function through its influence on the estimated LfSEVIRI and thus on the CFs - resolution enhancement reduced clear ocean pixels at the GERB nominal spatial resolution ( temporal matching between GERB and SEVIRI)

  15. ARG Comparison Unscreened Cloudy pixels

  16. ARG Comparison GERB spectral response function ? Unscreened Cloudy pixels

  17. ARG Comparison Unscreened Cloudy pixels

  18. Direct unfiltering Surface type dependent: ocean, vegetation and desert surfaces The normalized unfilter factor is estimated constaint: X = 0  Y = 1 X = 1  Y = 0 Where a, b, c and d are SZA dependent X is the normalized filtered radiance Mean of the 5% lowest values SBDART unfilter factor Lcld cld Mean of the 5% highest values Loc oc SBDART filtered SW radiance

  19. ARG FF, FDUF and FUF computation RAL G2_L15A files LF SZA, VZA, RAA RMIB G2_SEV1_L20S files Surface type  Cloud cover, cloud amount, cloud phase  LUF, FUF Assuming that the cloud optical depth was retrieved in the VIS 0.8 SEVIRI channel over ocean surface (less sensitive to the Rayleight scattering) FF and FDUF

  20. ARG FF, FDUF and FUF computation WARNING: The GERB PSF is applied in each of the RMIB G2_SEV1_L20S file fields. Not defined FFFDUFFUF

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