gerb thermal flux regional bias: detection and correction by comparison with ceres
DESCRIPTION
GERB thermal flux regional bias: detection and correction by comparison with CERES. S. Dewitte Royal Meteorological Institute of Belgium. Overview. Methodology Night time GERB CERES comparison Day time GERB CERES comparison MS5 MS7 comparison Validation ADM corrections. Methodology. - PowerPoint PPT PresentationTRANSCRIPT
GIST, 27-29/4/2005
GERB thermal flux regional bias: detection and correction by comparison with CERES
S. Dewitte
Royal Meteorological Institute of Belgium
GIST, 27-29/4/2005
Overview
Methodology Night time GERB CERES comparison Day time GERB CERES comparison MS5 MS7 comparison Validation ADM corrections
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Methodology Radiative flux at the top of the atmosphere: F (W/m2) Satellite observations: radiances L (W/m2sr) Satellite viewing zenith angle vz
F = L (vz) / R(vz)
GERB: fixed vz
Validation GERB fluxes: comparison with CERES fluxes with variable vz
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Used data GERB: ARG fluxes, SEVIRI as imager,
Version 2 CERES FM3: RAPS or GERB mode or
special scan, use of inflight calibration 1-6/2004 use of night and day data for thermal fluxes CERES data is colocated to nearest GERB
ARG pixel
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Regional difference – night time
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GERB – CERES difference fit
Impose linear variation with vz :f(vz)=(52.5°- vz)/ 52.5°
Fit difference as function of GERB flux:Fgerb-Fceres=a(Fgerb). f(vz)+b(Fgerb)
a(Fgerb) = GERB nadir error
Corrected GERB flux = Fgerb - a(Fgerb) . f(vz)
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Difference versus flux – night time
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All scenes – night time
Before correction After correction
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Daytime LW comparison
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Day and night time LW nadir error
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MS7 – MS5 difference fit
OLR estimate from MS5: Fms5
OLR estimate from MS7: Fms7
Comparison for July 2004 Fit difference as function of MS7 flux:
Fms7-Fms5=a(Fms7). f(vz,ms7)-b(Fms7).f(vz,ms5)+c(Fms7)
a(Fms7) = MS7 nadir error b(Fms7) = MS5 nadir error
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Without correction
Cold cloud correction
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Full correction
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Conclusions Theoretical thermal ADM errors are
identified from comparsions of– Night time GERB / CERES FM3 – Day time GERB / CERES FM3 – MS5 / MS7
The remaining differences are– within +/- 15 W/m2 over hot desert– within +/- 5 W/m2 elsewhere