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Understanding the Geostationary Earth Radiation Budget (GERB) Experience

Explore the vital role of GERB in measuring Earth Radiation Budget, improving climate models, and climate monitoring. Learn about GERB instrument, data processing, and its usage prospects.

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Understanding the Geostationary Earth Radiation Budget (GERB) Experience

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  1. Overview of the “Geostationary Earth Radiation Budget (GERB)” Experience. Nicolas Clerbaux Royal Meteorological Institute of Belgium (RMIB) In collaboration with: Imperial College, UK. Rutherford Appleton Laboratory (RAL), UK. GERB International Science Team (GIST).

  2. What it GERB ? • New instrument on the Meteosat Second Generation satellites of EUMETSAT, • First broadband imager radiometer observing the Earth from a geostationary satellite

  3. Outline of the talk • The GERB mission/science goals : why we need new measurements of the Earth Radiation Budget (ERB), • Interest of the Meteosat field-of-view, • GERB instrument, data processing, derived products and current status, • Examples of GERB data usage

  4. The Earth Radiation Budget (ERB)

  5. Diurnal and synoptic variability Uganda Kenya Lake Victoria Rwanda Burundi Congo Tanzania Meteosat-8 images – 12 July 2004

  6. GERB Mission Science goals • Measurement of the ERB with high temporal sampling thanks to the geostationary orbit. • Improvement of climate models by better understanding the role of clouds and water vapour in the ERB, • Improvement of Numerical Weather Prediction (NWP) models by data assimilation or near real-time validation, • Synergy with low orbit satellites observations: improvement of the diurnal model, • Climate monitoring in the frame of the EUMETSAT Satellite Application Facility on Climate Monitoring (CM-SAF).

  7. Interest of the Meteosat Field-of-View (1/2) Aerosols Contrails Tropical Convection Cirrus Also: desertification, African monsoon, marine stratocumulus, vulcaneos, biomass burning, …

  8. Interest of the Meteosat Field-of-View (2/2) Well-mixed greenhouse gases Radiative effect of aerosols blue: cooling effect red: warming effect unit : W/m² Mineral dust Biomass burning

  9. GERB instrument, data processing, derived products and status • Characteristics • Scanning mechanism • Instrument data • Data processing • Derived images of solar and thermal flux • Current data status

  10. GERB characteristics WAVEBANDSTotal: 0.32 µm - 100.0 µm Shortwave, SW: 0.32 µm - 4.0 µm Longwave, LW (by subtraction): 4.0 µm - 100.0 µm RADIOMETRYSW LW Absolute Accuracy: < 1.0 % < 1.0 % Signal/Noise: 1250 400 Dynamic Range: 0-380 W m-2 sr-1 0-90 W m-2 sr-1 SPATIAL SAMPLING44.6  39.3 km (NS  EW) at nadir TEMPORAL SAMPLING15 minute SW and LW fluxes CYCLE TIMEFull Earth disc, both channels in 5 minutes CO-REGISTRATIONSpatial: 3 km wrt SEVIRI at satellite sub-point Temporal: Within 15 min of SEVIRI at each pixel INSTRUMENT MASS25 kg POWER 35 W DIMENSIONS 476 mm  275 mm  345 mm

  11. GERB scanning Satellite rotation period = 0.6 s 282 steps for full Earth disc = 169.2 s 2 channels: Total Total+quartz filter (SW) Average three scans in each channel to improve S/N Total repeat time = 169.2*6 ~ 17 min. 256 detector pixels 256 detector pixels Between each Earth scan, internal BB measurement taken for calibration At correct viewing geometry, calibration monitor records scattered solar light as a relative measure over time 262 steps 282 steps

  12. Measured Radiance Images total [W/m²/sr] shortwave [W/m²/sr]

  13. GERB data processing • Geolocation and calibration (RAL) • Radiance unfiltering: correction for the instrument spectral response f(l). • Conversion in flux: angular modelling of the radiation field • Scene identification (surface, cloudiness,…) • Application of angular models • Enhancement of the spatial resolution: 50km ->10km • Near real-time dissemination by RMIB • Long term archiving and dissemination (RAL) At the RMIB (Brussels)

  14. Derived Fluxes Images (50km) Thermal [W/m²] Solar [W/m²]

  15. Current Data Status • GERB acquisition on Meteosat-8 started December 2002 and is ongoing, • The instrument is operating well, is stable and the measurements have low noise • Cross-calibration with other instruments (CERES) indicates good performances of the instrument • GERB data processing is still under validation, public release expected for end of 2005. • GERB data will be available to the scientific community free of charge.

  16. Image courtesy NASA Example of usage (1/2) GERB solar flux MODIS image 27 January 2003

  17. Example of usage (2/2) UK-MO Unified Model GERB Solar Flux Thermal Flux (Courtesy UK Met Office)

  18. Conclusions • The GERB data is unique! • European initiative in operational climate monitoring • Long term mission (+/- 15 years): GERB instrument will fly on Meteosat-9, -10 and -11 • Interest for climate modelling and meteorology • Importantcontribution of the RMIB. • More info at: http://gerb.oma.be

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