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| Titel |
Retrieval of atmospheric CO2 from satellite near-infrared nadir spectra in a scattering atmosphere |
| VerfasserIn |
M. Reuter, M. Buchwitz, O. Schneising, H. Bovensmann, J. P. Burrows |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250019331
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| Zusammenfassung |
| Atmospheric CO2 is the dominant anthropogenic greenhouse gas. Satellite measurements of
the CO2 mixing ratio (XCO2) derived from the SCIAMACHY instrument aboard
ENVISAT and in the future from OCO and GOSAT can provide valuable information to
quantify regional CO2 sources and sinks. Such an application requires high accuracy
and precision in the order of 1% or better to provide an added value compared to
the highly accurate but sparse ground-based measurement network. XCO2 can
be derived by simultaneously retrieving the atmospheric column of CO2 and O2.
Therefore, simulated sun normalized radiance spectra within the O2-A absorption
band at around 760nm and of the CO2 absorption band at 1580nm can be fitted to
SCIAMACHY measurements. Unfortunately, both bands have a relatively large
spectral distance and show also large differences of the strength of absorption. For
this reason, path length modifications due to scattering by aerosols and clouds in
both bands are also not identical, resulting in possible retrieval errors of XCO2.
Sub-visible cirrus clouds with an optical depth of 0.03 can already significantly
affect the retrieval. SCIAMACHY measurements within the CO2 band do not hold
enough information to correct for this effect. However, valuable information about
cirrus clouds can potentially be obtained from SCIAMACHY measurements in
the O2-A band. We will present an optimal estimation based retrieval scheme that
accounts for cirrus clouds by transferring cirrus information obtained from the O2-A
band to the CO2 band. Additionally, the algorithm is able to account for a priori
information to further constrain the inversion. In this context, we will present statistics of
cirrus fraction, optical depth, and effective height obtained from CALIPSO data. |
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