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| Titel |
On the use of satellite-derived CH4 : CO2 columns in a joint inversion of CH4 and CO2 fluxes |
| VerfasserIn |
S. Pandey, S. Houweling, M. Krol, I. Aben, T. Röckmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 15 ; Nr. 15, no. 15 (2015-08-03), S.8615-8629 |
| Datensatznummer |
250119945
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| Publikation (Nr.) |
 copernicus.org/acp-15-8615-2015.pdf |
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| Zusammenfassung |
| We present a method for assimilating total column CH4 : CO2 ratio
measurements from satellites for inverse modeling of CH4 and CO2 fluxes
using the variational approach. Unlike conventional approaches, in which
retrieved CH4 : CO2 are multiplied by model-derived total column
CO2 and only the resulting CH4 is assimilated, our method assimilates
the ratio of CH4 and CO2 directly and is therefore called the ratio
method. It is a dual tracer inversion, in which surface fluxes of CH4 and
CO2 are optimized simultaneously. The optimization of CO2 fluxes turns
the hard constraint of prescribing model-derived CO2 fields into a weak
constraint on CO2, which allows us to account for uncertainties in CO2.
The method has been successfully tested in a synthetic inversion setup. We
show that the ratio method is able to reproduce assumed true CH4 and
CO2 fluxes starting from a prior, which is derived by perturbing the true
fluxes randomly. We compare the performance of the ratio method with that of
the traditional proxy approach and the use of only surface measurements for
estimating CH4 fluxes. Our results confirm that the optimized CH4
fluxes are sensitive to the treatment of CO2, and that hard constraints on
CO2 may significantly compromise results that are obtained for CH4. We
find that the relative performance of ratio and proxy methods have a regional
dependence. The ratio method performs better than the proxy method in regions
where the CO2 fluxes are most uncertain. However, both ratio and proxy
methods perform better than the surface-measurement-only inversion,
confirming the potential of spaceborne measurements for accurately
determining fluxes of CH4 and other greenhouse gases
(GHGs). |
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