GERB fluxes – Method for Regional Validation

Nicolas Clerbaux and RMIB GERB teamRoyal Meteorological Institute of Belgium

GIST 21 – Boulder – April 2 2004

Content

• Brief summary of the GERB radiance-to-flux conversions– Shortwave– Longwave

• Regional Validation – Method– Data– Illustrations– Additional things to do

• Conclusions

GERB Shortwave flux

• CERES TRMM SW ADM selection based on the RMIB-SEVIRI scene identification. Note:

– No aerosol information– No snow ADM– No wind speed over ocean information

• CERES TRMM SW ADM application:– No interpolation in term of cloud properties (fraction,

optical depth and phase): use the bin value– Tri-linear interpolation in term of angles– Weighting in case of mixed surface types:

i

siii

sisvii )(θAω/)(θAφ),θ,(θRωR

Use of the 592 CERES-TRMMSW ADMs:

R

LF

),θ,(θRR 0c

Shortwave Angular Dependency Models

GERB Longwave Flux

• Regression in terms of SEVIRI (imager) NB thermal radiances

• Parameterisation using the SBDART radiative transfer model

)L,L,L,L,L,L,L,R(θR 13.4μ312μ210.8μ09.7μ.8.7μ.7.3μ.6.2μ.v

R

LF

Longwave Anisotropic Factor R

GERB Radiance-to-flux Validation• Needed before data release (date TBD), input for Quality Needed before data release (date TBD), input for Quality

SummarySummary• Validation of TRMM ADM applied on GEO data by Validation of TRMM ADM applied on GEO data by

Norman Loeb: performed on CERES-TRMM data for Norman Loeb: performed on CERES-TRMM data for 1998/2000 (no SEVIRI scene id.!)1998/2000 (no SEVIRI scene id.!)

• GERB always observes a region from the same GERB always observes a region from the same direction-> need of a regional validationdirection-> need of a regional validation

• Should be performed for different (all) positions of the Should be performed for different (all) positions of the sun in the sky sun in the sky

• Method: similar to the Direct Integration test but with Method: similar to the Direct Integration test but with angular sampling provides by CERES in RAPS modeangular sampling provides by CERES in RAPS mode

-> need a preliminary regional comparison of the unfiltered radiances-> need a preliminary regional comparison of the unfiltered radiances

Method• CERES in RAPS mode for a given time period (some months)• Collocated GERB measurements (GERB is continuous in space and time) • Direct Integration of the CERES data in regional box provides the averaged

“true flux” : <FDI>= int {cos v sin v <Lceres(v,)>}

or<FDI>= <Fceres>

• Comparison with the corresponding GERB mean flux in the box:<Fgerb >

• Regional analysis of the Difference/Ratio at 10:30 LT (Terra) and 1:30 LT (Aqua)

Data

• GERB: – Processed with SEVIRI since 19 Dec. 2003– Validation period Dec 2003 -> June 2004– Some scene id. problems fixed March 2004

• CERES:– FM2 (Terra) and FM3 (Aqua) for RAPS mode– ES8 Edition 1, ES8 Edition 2, SSF

Illustrations of the method using ES8 Ed. 1 data for 19/12/2003 -> 31/02/2004

Terra FM2 coverage (52 days) Aqua FM3 coverage (23days)

Ratio LW – GERB-2/CERES FM3 (day and

night) – 4*4 ARG pixels Mean GERB

Mean CERES

Ratio LW – GERB-2/CERES FM2 (night only) – 4*4 ARG

pixels

Ratio SW – GERB-2/CERES FM2 – 4*4 ARG pixels

Shortwave (2) – GERB-2/CERES FM3 – 4*4 ARG pixels

Additional things to do

• Analysis of spatial/angular/temporal sampling

• Regional analysis of unfiltered radiances

• Switch to ES8 Edition 2 and SSF when available

• Regional analysis of difference when the true flux <Fceres> is provided by the ES8 files or by the SSF (one month in 2002?).

Conclusions

• Regional validation of the GERB fluxes will be performed.

• Based on CERES RAPS data -> only 4 local time.

• Need additional analysis in term of radiance for a correct interpretation of the results.

• First results expected for this summer.