gerb sw fluxes: an update (clear ocean sw radiances and fluxes in the reprocessed v999 june 04 data)...
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GERB SW fluxes: an update(Clear ocean SW radiances and fluxes in the
reprocessed V999 June 04 data)
CCédric Bertrandédric Bertrand
GIST 24 14-16th December, Imperial College, London, U.K.
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RECAP: unfiltering
New spectral response function
New spectral conversion:
LLLL
F
GERBF
SEVIRI
UF
SEVIRIUF
GERB.
where:
dILUF
SW
0
dISL
F
SW
0
= wavelength (m)I= reflected solar radiance (Wm-2.Sr-1.m-1)S=spectral response function (0 S 1)
LSEVIRI = a + b1 L0.6 + b2 L0.8 + b3 L1.6 + c11 L20.6 + c21 L0.8L0.6 + c22 L2
0.8 + c31 L1.6L 0.6 + c32 L1.6 L 0.8 + c33 L2
1.6 !!!! fct of SZA ONLY !!!!!!!! fct of SZA ONLY !!!!
= unfilter factor
V002
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RECAP: unfiltering
Database of co-angular CERES and SEVIRI measurements(March, April and July 04 FM2/FM3 ES8 Edition 2 CERES data)
LSEVIRIUF (LCERES
UF = a + b L0.6 + c L0.8 + d L1.6 + e SZA sza 60°) with a, b, c, d and e surface types dependent
LSEVIRIF CAN NOT BE DETERMINED FROM CERES DATA
General case: LSEVIRI
F = a’ + b’ L0.6 + c’ L0.8 + d’ L1.6 + e’ SZA
Lc
LbaSBDART 2
6.06.0
""" (a", b" and c" = f(SZA,VZA,RAA))
V999:
Clear Ocean: LSEVIRIF = LSEVIRI
UF/SBDART
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RECAP: angular conversion
),,,(),,,(
),,()(
mvmsmjmvmsmjadm
mvmsmmsm wsCF
wsRLF
Radm = clear ocean wind speed dependent CERES-TRMM BB ADM anisotropic correction factor
If (glint angle) < 25°
),,,()()( mvmsmjsmadmsm wsCFFF
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FADM FDUF FUF
FADM FF FDUF FUF
FF
F l.n – F l.n-2:00 (W.m-2)
F l.n – F l.n+2:00 (W.m-2)
ARGARG JUNE 04JUNE 04
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F l.n – F l.n-2:00 (W.m-2)FADM
FADM FS3
FG3
FG3
F l.n – F l.n+2:00 (W.m-2)
FS3
3x3 SEVIRI3x3 SEVIRI JUNE 04JUNE 04
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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 = Lf
GERB/LfSEVIRI
FIRST: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) = (xy PSF(i, j, x, y) . FS3 (x, y)). CFL(i, j)
CFL(i, j) = correction of SEVIRI by GERB
SECOND:SECOND: improvement of the spatial resolution of GERB fluxes by use of SEVIRI high resolution information
FGERB(i, j) = xy PSF(i, j, x, y) . CFH(x, y) . FS3 (x, y)
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RECAP: resolution enhancement (II)
FINALLY:FINALLY: GERB flux at the 3 x 3 SEVIRI pixels resolution is given by FG3(x, y) = CFH(x, y) . FS3
(x, y)
use of LfADM
(x,y) rather than LfSEVIRI(x,y)
in the CFL(i,j) computation.
To reduce the impact of the SEVIRI spectral conversion in the estimation of the GERB SW fluxes at the 3x3 SEVIRI pixels resolution:
SBDART
UF
ADMF
ADMLL
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
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F l.n – F l.n-2:00 (W.m-2)FS3
FS3 FG3
FG3_ADM_L
FG3_ADM_L
F l.n – F l.n+2:00 (W.m-2)
FG3
3x3 SEVIRI3x3 SEVIRI JUNE 04JUNE 04
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LS3/LADM LG3/LADM
05.06.04
SZA RAAVZA
UNFILTERED RADIANCE RATIO
LG3_ADM_L/LADM
-180
-90
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FS3/FADM FG3/FADM
05.06.04
SZA RAAVZA
FLUX RATIO
FG3_ADM_L/FADM
-180
-90
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ARG: 05-06-04
LUF/LADM FUF/FADM
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GERB and SEVIRI images recorded at times temporal matching neededScene types independent
Resolution enhancement limitations:
GERB pixel
3x3 SEVIRI pixels footprint
100% clear
100% cloudy
Clear ocean S3 footprint for which the CFH(x,y) will be cloud contaminated
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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 Lf
SEVIRI and thus on the CFs
- resolution enhancement reduced clear ocean pixels at the GERB nominal spatial resolution ( temporal matching between GERB and SEVIRI)
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ARG Comparison
Unscreened
Cloudy pixels
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ARG Comparison
Unscreened Cloudy pixels
GERB spectral response function ?
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ARG Comparison
UnscreenedCloudy pixels
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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
cldoc
cldY
)()( 2cXd
cXbaY
LLLLXcldoc
cld
SBDART filtered SW radiance
SB
DA
RT
unf
ilte
r fa
ctor
Mean of the 5% highest values Lcld
cld
Mean of the 5% lowest
valuesLoc
oc
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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
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ARG FF, FDUF and FUF computation
WARNING: The GERB PSF is applied in each of the RMIB G2_SEV1_L20S file fields.
Not defined
FFFF FFDUFDUF FFUFUF
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