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| Titel |
The ACOS CO2 retrieval algorithm – Part II: Global XCO2 data characterization |
| VerfasserIn |
D. Crisp, B. M. Fisher, C. O'Dell, C. Frankenberg, R. Basilio, H. Bösch, L. R. Brown, R. Castano, B. Connor, N. M. Deutscher, A. Eldering, D. Griffith, M. Gunson, A. Kuze, L. Mandrake, J. McDuffie, J. Messerschmidt, C. E. Miller, I. Morino, V. Natraj, J. Notholt, D. M. O'Brien, F. Oyafuso, I. Polonsky, J. Robinson, R. Salawitch, V. Sherlock, M. Smyth, H. Suto, T. E. Taylor, D. R. Thompson, P. O. Wennberg, D. Wunch, Y. L. Yung |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 5, no. 4 ; Nr. 5, no. 4 (2012-04-02), S.687-707 |
| Datensatznummer |
250002773
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| Publikation (Nr.) |
 copernicus.org/amt-5-687-2012.pdf |
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| Zusammenfassung |
| Here, we report preliminary estimates of the column averaged carbon dioxide
(CO2) dry air mole fraction, XCO2, retrieved from spectra recorded
over land by the Greenhouse gases Observing Satellite, GOSAT (nicknamed
"Ibuki"), using retrieval methods originally developed for the NASA
Orbiting Carbon Observatory (OCO) mission. After screening for clouds and
other known error sources, these retrievals reproduce much of the expected
structure in the global XCO2 field, including its variation with
latitude and season. However, low yields of retrieved XCO2 over
persistently cloudy areas and ice covered surfaces at high latitudes limit
the coverage of some geographic regions, even on seasonal time scales.
Comparisons of early GOSAT XCO2 retrievals with XCO2 estimates
from the Total Carbon Column Observing Network (TCCON) revealed a global,
−2% (7–8 parts per million, ppm, with respect to dry air) XCO2
bias and 2 to 3 times more variance in the GOSAT retrievals. About half of
the global XCO2 bias is associated with a systematic, 1%
overestimate in the retrieved air mass, first identified as a global +10 hPa
bias in the retrieved surface pressure. This error has been attributed to
errors in the O2 A-band absorption cross sections. Much of the
remaining bias and spurious variance in the GOSAT XCO2 retrievals has
been traced to uncertainties in the instrument's calibration, oversimplified
methods for generating O2 and CO2 absorption cross sections, and
other subtle errors in the implementation of the retrieval algorithm. Many
of these deficiencies have been addressed in the most recent version (Build
2.9) of the retrieval algorithm, which produces negligible bias in XCO2
on global scales as well as a ~30% reduction in variance.
Comparisons with TCCON measurements indicate that regional scale biases
remain, but these could be reduced by applying empirical corrections like
those described by Wunch et al. (2011b). We recommend that such corrections
be applied before these data are used in source sink inversion studies to
minimize spurious fluxes associated with known biases. These and other
lessons learned from the analysis of GOSAT data are expected to accelerate
the delivery of high quality data products from the Orbiting Carbon
Observatory-2 (OCO-2), once that satellite is successfully launched and
inserted into orbit. |
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