XCO 2 observations using satellite measurements with moderate spectral resolution: investigation using GOSAT and OCO-2 measurements
Atmospheric measurement techniques, vol. 13, pp. 713–729
Abstract
In light of the proposed space segment of Europe's future CO 2 monitoring system, we investigate the spectral resolution of the CO 2 spectrometer, which measures earthshine radiance in the three relevant spectral bands at 0.76, 1.61, and 2.06 µm. The Orbiting Carbon Observatory-2 (OCO-2) mission covers these bands with fine spectral resolution but limited spatial coverage, which hampers the monitoring of localized anthropogenic CO 2 emission. The future European CO 2 monitoring constellation, currently undergoing feasibility studies at the European Space Agency (ESA), is targeting a moderate spectral resolution of 0.1, 0.3, and 0.3–0.55 nm in the three spectral bands with a high signal-to-noise ratio (SNR) as well as a spatial resolution of 4 km 2 and an across-track swath width >250 km. This spectral and radiometric sizing is deemed to be favorable for large-swath imaging of point sources of CO 2 emission. To assess this choice, we use real and synthetic OCO-2 satellite observations, which we spectrally degrade to the envisaged lower spectral resolution. We evaluate the corresponding CO 2 retrieval accuracy by taking the Total Carbon Column Observing Network (TCCON) observations as reference. Here, a lower spectral resolution enhances the scatter error of the retrieved CO 2 column mixing ratio (XCO 2 ) but has little effect on the station-to-station variation in the biases. We show that the scatter error gradually increases with decreasing spectral resolution. Part of the scatter error increase can be attributed to the retrieval noise error which can be compensated for by a future instrument with improved SNR. Moreover, we consider the effect of the reduced spectral resolution on the capability to capture regional XCO 2 variations and XCO 2 plumes from selected OCO-2 orbits. The investigation using measurements from the Greenhouse gases Observing SATellite (GOSAT) and synthetic measurements confirms our finding and indicates that one major source of uncertainties regarding CO 2 retrieval is the insufficient information on aerosol properties that can be inferred from the observations. We hence recommend the implementation of simultaneous, co-located measurements that have a larger information content on aerosols with an auxiliary instrument in the future European observing system.
Authors 7
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Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
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Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
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European Space Agency · European Space Research and Technology Centre
Affiliation as printed
European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands
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European Space Agency · European Space Research and Technology Centre
Affiliation as printed
European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands
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Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
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Affiliation as printed
Institut für Umweltphysik, Heidelberg University, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany
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Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
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