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| Titel |
Assessing 5 years of GOSAT Proxy XCH4 data and associated uncertainties |
| VerfasserIn |
Robert Parker, Hartmut Boesch, Peter Somkuti, Paul Palmer, Liang Feng, Peter Bergamaschi, Frédéric Chevallier |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110208
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| Publikation (Nr.) |
 EGU/EGU2015-10186.pdf |
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| Zusammenfassung |
| We present 5 years of GOSAT XCH4 retrieved using the "proxy" approach. The Proxy XCH4
data is validated against ground-based TCCON observations and is found to be of
high-quality with a small bias of 4.8 ppb (~0.27%) and a single-sounding precision of 13.4
ppb (~0.74%). For the first time the XCH4/XCO2 ratio component of the Proxy retrieval is
validated (bias of 0.014 ppb/ppm (~0.3%), single-sounding precision of 0.033 ppb/ppm
(~0.72%).
The uncertainty relating to the model XCO2 component of the Proxy XCH4 is assessed
through the use of an ensemble of XCO2 models. While each individual XCO2 model is
found to agree well with the TCCON validation data (r = 0.94-0.97), it is not possible to
select one model as the best based on these comparisons. The median XCO2 value of the
ensemble has a smaller scatter against TCCON than any of the individual models (0.92 ppm)
whilst maintaining a small bias (0.15 ppm). This model median XCO2 is used to calculate the
Proxy XCH4 with the maximum deviation from the median used as an estimate of the
uncertainty.
We compare this uncertainty to the a posteriori retrieval error and find typically that the
model XCO2 uncertainty becomes significant during summer months where the a posteriori
error is at its lowest.
We assess the significance of these uncertainties on flux inversion by comparing
against the GOSAT-MACC XCH4 differences. We find that for the majority of
regions the differences are much larger than the estimated uncertainties. Our findings
show that useful information will be provided to the inversions for the majority of
regions in addition to that already provided by the assimilated in-situ measurements. |
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