Overview of the “Geostationary Earth Radiation Budget (GERB)”

Experience.

Nicolas ClerbauxRoyal Meteorological Institute of Belgium (RMIB)

In collaboration with:Imperial College, UK.

Rutherford Appleton Laboratory (RAL), UK. GERB International Science Team (GIST).

What it GERB ?• New instrument on the

Meteosat Second Generation satellites of EUMETSAT,

• First broadband imager radiometer observing the Earth from a geostationary satellite

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

The

Ear

th R

adia

tion

Bud

get (

ER

B)

Diurnal and synoptic variability

Lake Victoria

Congo Tanzania

KenyaUganda

Rwanda

Burundi

Meteosat-8 images – 12 July 2004

GERB Mission• 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).

Science goals

Interest of the Meteosat Field-of-View (1/2)

Also: desertification, African monsoon, marine stratocumulus, vulcaneos, biomass burning, …

Aerosols

Tropical Convection

Contrails

Cirrus

Biomass burning Mineral dust

Well-mixed greenhouse gases

Radiative effect of aerosols

blue: cooling effectred: warming effectunit : W/m²

Interest of the Meteosat Field-of-View (2/2)

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

GERB characteristicsWAVEBANDS Total: 0.32 µm - 100.0 µm

Shortwave, SW: 0.32 µm - 4.0 µm

Longwave, LW (by subtraction): 4.0 µm - 100.0 µm

RADIOMETRY SW 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 SAMPLING 44.6 39.3 km (NS EW) at nadir

TEMPORAL SAMPLING 15 minute SW and LW fluxes

CYCLE TIME Full Earth disc, both channels in 5 minutes

CO-REGISTRATION Spatial: 3 km wrt SEVIRI at satellite sub-point

Temporal: Within 15 min of SEVIRI at each pixel

INSTRUMENT MASS 25 kg

POWER 35 W

DIMENSIONS 476 mm 275 mm 345 mm

Average three scans in each channel to improve S/N

Total repeat time = 169.2*6 ~ 17 min.

256

dete

ctor

pix

els

262 steps

256

dete

ctor

pix

els

282 steps

Satellite rotation period = 0.6 s

282 steps for full Earth disc = 169.2 s

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

2 channels: Total Total+quartz filter (SW)

GERB scanning

Measured Radiance Imagesshortwave [W/m²/sr] total [W/m²/sr]

GERB data processing

• Geolocation and calibration (RAL)• Radiance unfiltering: correction for the

instrument spectral response • 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 theRMIB

(Brussels)

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

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.

Image courtesy NASA

GERB solar flux MODIS image

Example of usage (1/2)

27 January 2003

UK-MO Unified Model GERB

(Courtesy UK Met Office)

Solar Flux

Thermal Flux

Example of usage (2/2)

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

• Important contribution of the RMIB.

• More info at: http://gerb.oma.be