Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processing

Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processingNicolas Clerbaux & RMIB GERB Team.

GIST 26, RAL

3 and 4 May 2007

MSG1 -> MSG2 transitionNew GERB instrument but also new SEVIRI imager

Are the SEVIRI scene identifications consistent?GERB unfilteringGERB SW ADM selectionGERB LW angular modelling GERB scene identificationGERB dust flag and AOD retrieval

Are the GERB-likes (SEVIRI NB-to-BB) consistent?RGP GERB geolocationGERB unfilteringGERB resolution enhancementuse of GERB-like data for monthly means

Structure of the talkIntercomparison of level 1.5 SEVIRI datareflectance for visible channelsBT and radiance for thermal channels

Intercomparison of GERB scene identificationcloud fraction, cloud optical depth cloud phaseclear sky reflectanceLW anisotropic factordust flag and AOD retrieval

Intercomparison of the GERB-like BB quantitiessolar and thermal radiancessolar and thermal fluxes

Conclusions

The MSG1 and MSG2 data look very similar... natural colorair mass

Visible bands spectral response and effective central wavelength for MSG-1 and MSG-2MSGs=0.639mMSG2s=0.640m

MSGs=0.809mMSG2s=0.807m

MSGs=1.635mMSG2s=1.635m

0.6 m reflectance intercomparisonratio MSG2/MSG1

0.6 m reflectance intercomparison saturations for MSG2Max 0.6 m reflectance at nadir and d=1 A.U. is

MSG1 : 1.082

MSG2 : 0.942

Software fix: accept saturation if SZA

6.2 m brightness temperature intercomparisonratio MSG2/MSG1

12 m brightness temperature intercomparisonratio MSG2/MSG1

Spectral radiance comparison

ratio MSG2/MSG1WV 6.2 : 1.002WV 7.3 : 0.992IR 8.7 : 0.999IR 9.7 : 0.994IR 10.8 : 1.000 IR 12.0 : 0.996IR 13.4 : 0.974

-> in general MSG-2 is close or a bit lower than MSG-1, CO2 is significantly lower

Summary for level 1.5 MSG-2/MSG-1 intercomparisonvisible 0.6m and 0.8m channels : 1 to 2% higher reflectancenear IR channel (1.6m): very closethermal channels: very close or a bit lower except the CO2 channel (13.4m) which is significantly colder (0.5% in BT , 2.5% in radiance)

0.6m is often saturated over thick cloudresidual stripes in the WV 6.2m channel

Intercomparison of scene identificationsurface type is exactly the same (same rectification grid)cloud fractioncloud optical depthcloud phaseclear sky reflectance imagesLW angular modelingHelen Brindley 's dust flagAerosol retrieval with Ignatov look-up-table for the 0.6m, 0.8m and 1.6m channels

Cloud fraction

Cloud optical depth (log)

Cloud phase (0=pure water 1=pure ice)

Clear sky reflectance intercomparison (ratio to model)VIS 0.6VIS 0.8

LW ADM due to the change in NB radiances F=p L / R(q,L6.2, L10.8, L12,L13.4) FMSG1'/FMSG1

Ratio of the flux for a same BB radiance L but for simulated differences between MSG1 and MSG2 NB radiances in the 6.2m, 10.8m, 12m, 13.4m channels

Small increase of the anisotropy (0.2%).

Dust FlagMSG2MSG1

AOD in 0.6 m channel

Summary for scene identificationcloud fraction very similarcloud optical depth slightly higher (2%) due to the 0.6m and 0.8m reflectancescloud phase very similarLW angular modelling close, small difference in the good direction (increase of the limb-darkening). dust flag may differ in some semi-transparent situations AOD 2% higher at 0.6m , 0.6% higher at 0.8 m and 1.6% lower at 1.6 m. Ratio of AOD does not correspond to ratio in reflectance.

Intercomparison of broadband quantitiesGERB-like BB radiances (NB->BB)reflected solaremitted thermal

GERB-like BB fluxes (NB->BB + ADMs) reflected solaremitted thermal

GERB-like Reflected Solar Radiance

GERB-like Emitted Thermal Radiance

GERB-like Reflected Solar Fluxratio MSG2/MSG1

GERB-like Emitted Thermal Fluxratio MSG2/MSG1

Summary for the broadband productssolar radiance MSG2/MSG1 = 1.012thermal radiance MSG2/MSG1 = 0.9964solar flux MSG2/MSG1 = 1.012thermal flux MSG2/MSG1 = 0.9954

Conclusions and future workstart of GERB-1 processing with SEVIRI on MSG2good consistency with MSG1, most of the differences are explained by the level 1.5 SEVIRI data intercomparison,GERB-like radiances and fluxes are a bit closer to the actual GERB productsTo be done: analysis of the influence of the SEVIRI radiance definition (change from spectral radiance to effective radiance in April 2008).

Intercomparison of SEVIRI data from MSG1 and MSG2 and implications for the GERB data processing

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