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| Titel |
Atmospheric greenhouse gases retrieved from SCIAMACHY: comparison to ground-based FTS measurements and model results |
| VerfasserIn |
O. Schneising, P. Bergamaschi, H. Bovensmann, M. Buchwitz, J. P. Burrows, N. M. Deutscher, D. W. T. Griffith, J. Heymann, R. Macatangay, J. Messerschmidt, J. Notholt, M. Rettinger, M. Reuter, R. Sussmann, V. A. Velazco, T. Warneke, P. O. Wennberg, D. Wunch |
| 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 ; 12, no. 3 ; Nr. 12, no. 3 (2012-02-09), S.1527-1540 |
| Datensatznummer |
250010645
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| Publikation (Nr.) |
 copernicus.org/acp-12-1527-2012.pdf |
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| Zusammenfassung |
SCIAMACHY onboard ENVISAT (launched in 2002) enables the
retrieval of global long-term column-averaged dry air mole
fractions of the two most important anthropogenic greenhouse
gases carbon dioxide and methane (denoted XCO2 and
XCH4). In order to assess the quality of the
greenhouse gas data obtained with the recently introduced v2
of the scientific retrieval algorithm WFM-DOAS, we present
validations with ground-based Fourier Transform Spectrometer
(FTS) measurements and comparisons with model results at eight
Total Carbon Column Observing Network (TCCON) sites
providing realistic error estimates of the satellite
data. Such validation is a prerequisite to assess the
suitability of data sets for their use in inverse modelling.
It is shown that there are generally no significant differences
between the carbon dioxide annual increases of SCIAMACHY
and the assimilation system CarbonTracker (2.00 ± 0.16 ppm yr−1
compared to 1.94 ± 0.03 ppm yr−1 on global average).
The XCO2 seasonal cycle amplitudes derived from SCIAMACHY
are typically larger than those from TCCON which are in
turn larger than those from CarbonTracker. The absolute values
of the northern hemispheric TCCON seasonal cycle amplitudes
are closer to SCIAMACHY than to CarbonTracker and the corresponding
differences are not significant when compared with SCIAMACHY, whereas
they can be significant for a subset of the analysed TCCON
sites when compared with CarbonTracker. At Darwin we find
discrepancies of the seasonal cycle derived from SCIAMACHY
compared to the other data sets which can probably be ascribed to
occurrences of undetected thin clouds. Based on the comparison with
the reference data, we conclude that the carbon dioxide data set
can be characterised by a regional relative precision (mean standard
deviation of the differences) of about 2.2 ppm and a relative
accuracy (standard deviation of the mean differences) of
1.1–1.2 ppm for monthly average composites within
a radius of 500 km.
For methane, prior to November 2005, the regional relative
precision amounts to 12 ppb and the relative accuracy is
about 3 ppb for monthly composite averages within the same
radius. The loss of some spectral detector pixels results in a
degradation of performance thereafter in the spectral range
currently used for the methane column retrieval. This leads to
larger scatter and lower XCH4 values are retrieved in the
tropics for the subsequent time period degrading the relative
accuracy. As a result, the overall relative precision is estimated
to be 17 ppb and the relative accuracy is in the range of about
10–20 ppb for monthly averages within a radius of 500 km.
The derived estimates show that the SCIAMACHY XCH4
data set before November 2005 is suitable for regional
source/sink determination and regional-scale flux uncertainty
reduction via inverse modelling worldwide. In addition, the
XCO2 monthly data potentially provide valuable information
in continental regions, where there is sparse sampling by surface
flask measurements. |
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