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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2019-232
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-232
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Aug 2019

Submitted as: research article | 23 Aug 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

XCO2 observations using satellite measurements with moderate spectral resolution: Investigation using GOSAT and OCO-2 measurements

Lianghai Wu1, Joost aan de Brugh1, Yasjka Meijer2, Bernd Sierk2, Otto Hasekamp1, Andre Butz3, and Jochen Landgraf1 Lianghai Wu et al.
  • 1SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, the Netherlands
  • 2European Space Agency, Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands
  • 3University Heidelerg, Institut für Umweltphysik, Im Neuenheimer Feld 229, 69120 Heidelberg, Germany

Abstract. In light of the proposed space segment of Europe's future CO2 monitoring system, we investigate the spectral resolution of the CO2 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 CO2 emission. The future European CO2 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 high signal-to-noise (SNR) ratio. This spectral and radiometric sizing is deemed to be favorable for large-swath imaging of point-sources of CO2 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 CO2 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 CO2 column mixing ratio (XCO2) but has little effect on the station-to-station variation of the biases. We show that the scatter error gradually increases when decreasing spectral resolution. Part of the scatter error increase can be attributed to the retrieval noise error which can be compensated by a future instrument with improved SNR. Moreover, we consider the effect of the reduced spectral resolution on the capability to capture regional XCO2 variations and XCO2 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 CO2 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 larger information content on aerosols with an auxiliary instrument in the future European observing system.

Lianghai Wu et al.
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Status: final response (author comments only)
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Lianghai Wu et al.
Lianghai Wu et al.
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