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Retrieval of atmospheric CO2 from satellite near-infrarednadir spectra in the frame of ESA’s climate change initiative

M.Reuter , O.Schneising , M.Buchwitz , J.Heymann, H.Bovensmann, J.P.BurrowsInstitute of Environmental Physics, University of Bremen, Germany

EMS, Berlin, September 2011

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e ESA’s GHG-CCI: Aims and Motivation

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e ESA’s GHG-CCI: Road Map

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e Two in-house algorithms

BESD (XCO2) WFMD (XCO2, XCH4)

Inversion Algorithm:Optimal Estimation;

Full Physics

Least-squares;

Light path Proxy

A-priori constraints:

Yes

Constant: CO2(p), aerosol,

cirrus, ...

Per pixel: P, T, H2O, ...

No

(constant atmosphere as

linearization point for RT)

Atmosphere: ECMWF US Standard (sev. H2O)

Aerosols: State vector (APS) Constant; AAI filter (CO2 only)

Clouds:State vector (CWP, CTH);

Filtering: MERIS 1x1 km2

RT cloud free;

Filtering: O2 & PMD (CO2 only)

Fit windows: Merged fit windows Independent fit windows

Radiative Transfer: SCIATRAN on-line SCIATRAN LUT

Speed: Slow (~15 min./pixel) Fast (~2 min./orbit)

Optimized for: Accuracy Compromise accuracy/speed

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e BESD XCO2

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e Validation with TCCON FTS measurements

350km

Park Falls, USA

350km

Bremen, Germany

350km

Darwin, Australia

350km

Lauder, New Zealand

• Restriction to a limited validation data set due to computational costs• Only 4 TCCON sites measured in the full period 2006-2010

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e Comparison with FTS, CarbonTracker, GOSAT

Overall good agreement betweenSCIAMACHY, GOSAT, FTS

and CarbonTracker

No statistical significantregional biases

Single measurementprecision ~2.5ppm

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e Comparison with FTS, CarbonTracker, GOSAT

Smoothed Results show:Good agreement of year-to-year increase and seasonal amplitude.

(Data density allows smoothing only at Park Falls and Darwin)

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e WFMD XCO2

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e Global increase

• Computational costs are orders of magnitude lower• Processing of global data easily possible• A global dataset 2003-2009 is available• Similar annual global patterns• Continuous year-to-year increase of global XCO2

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e CO2 uptake by growing vegetation

Mean wind direction

LongitudeWest East

XCO2

Fnet

Assumption:XCO2 gradient in wind direction

approximately proportionalto net surface flux Fnet

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e CO2 uptake by growing vegetation

Calculation of gradients aboveboreal forests (Canada+Russia):Good agreement with CarbonTracker(year-to-year progression and size)

Canada: larger neg. gradientssuggest stronger CO2 uptake

Russia: less strong gradientssuggest weaker CO2 uptake

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http://www.esa-ghg-cci.org/Intercomparison with other XCO2 algorithms

• Within the GHG CCI several different XCO2 retrieval techniques are involved: BESD, WFMD, and the algorithms of SRON, University of Leicester, ACOS, and NIES

• First inter-comparisons with FTS measurements show many similarities but also differences which have to be analyzed

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http://www.esa-ghg-cci.org/

THANKS!