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| Titel |
Mid-upper tropospheric methane retrieval from IASI and its validation |
| VerfasserIn |
X. Xiong, C. Barnet, E. S. Maddy, A. Gambacorta, T. S. King, S. C. Wofsy |
| 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 ; 6, no. 9 ; Nr. 6, no. 9 (2013-09-03), S.2255-2265 |
| Datensatznummer |
250085053
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| Publikation (Nr.) |
 copernicus.org/amt-6-2255-2013.pdf |
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| Zusammenfassung |
| Mid-upper tropospheric methane (CH4), as an operational product at
NOAA's (National Oceanic and Atmospheric Administration) Comprehensive Large
Array-data Stewardship System (CLASS), has been retrieved from the Infrared
Atmospheric Sounding Interferometer (IASI) since 2008. This paper provides a
description of the retrieval method and the validation using 596 CH4
vertical profiles from aircraft measurements by the HIAPER Pole-to-Pole
Observations (HIPPO) program over the Pacific Ocean. The number of degrees
of freedom for the CH4 retrieval is mostly less than 1.5, and it
decreases under cloudy conditions. The retrievals show greatest sensitivity
between 100–600 hPa in the tropics and 200–750 hPa in the mid- to high
latitude. Validation is accomplished using aircraft measurements (convolved
by applying the monthly mean averaging kernels) collocated with all the
retrieved profiles within 200 km and on the same day, and the results show
that, on average, a larger error of CH4 occurs at 300–500 hPa. The bias
in the trapezoid of 374–477 hPa is −1.74% with a residual standard
deviation of 1.20%, and at layer 596–753 hPa the bias is −0.69% with a residual standard deviation of
1.07%. The retrieval error is relatively larger in
the high northern latitude regions and/or under cloudy conditions. The main
reasons for this negative bias include the uncertainty in the spectroscopy
near the methane Q branch and/or the empirical bias correction, plus
residual cloud contamination in the cloud-cleared radiances. It is expected
for NOAA to generate the CH4 product for 20 + years using a similar
algorithm from three similar thermal infrared sensors: Atmospheric
Infrared Sounder (AIRS), IASI and the Cross-track Infrared Sounder (CrIS).
Such a unique product will provide a supplementary to the current
ground-based observation network, particularly in the Arctic, for monitoring
the CH4 cycle, its transport and trend associated with climate change. |
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