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| Titel |
Pressure broadening in the 2ν3 band of methane and its implication on atmospheric retrievals |
| VerfasserIn |
C. Frankenberg, T. Warneke, A. Butz, I. Aben, F. Hase, P. Spietz, L. R. Brown |
| 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 ; 8, no. 17 ; Nr. 8, no. 17 (2008-09-01), S.5061-5075 |
| Datensatznummer |
250006351
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| Publikation (Nr.) |
 copernicus.org/acp-8-5061-2008.pdf |
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| Zusammenfassung |
| N2-broadened half widths and pressure shifts were obtained for
transitions in the 2ν3 methane band. Laboratory measurements recorded at
0.011 cm−1 resolution with a Bruker 120 HR Fouriertransform
spectrometer were analysed from 5860 to 6185 cm−1. A
140 cm gas cell was filled with methane at room temperature and
N2 as foreign gas at pressures ranging from 125 to 900 hPa. A
multispectrum nonlinear constrained least squares approach based on Optimal
Estimation was applied to derive the spectroscopic parameters by
simultaneously fitting laboratory spectra at different ambient pressures
assuming a Voigt line-shape. At room temperature, the half widths ranged
between 0.030 and 0.071 cm−1 atm−1, and the pressure shifts
varied from –0.002 to –0.025 cm−1 atm−1 for transitions up
to J"=10. Especially for higher rotational levels, we find
systematically narrower lines than HITRAN predicts. The Q and R branch of the
new set of spectroscopic parameters is further tested with ground based
direct sun Fourier transform infrared (FTIR) measurements where systematic
fit residuals reduce by about a factor of 3–4. We report the implication of
those differences on atmospheric methane measurements using high-resolution
ground based FTIR measurements as well as low-resolution spectra from the
SCanning Imaging Absorption SpectroMeter for Atmospheric ChartographY
(SCIAMACHY) instrument onboard ENVISAT. We find that for SCIAMACHY, a
latitudinal and seasonally varying bias of about 1% can be introduced by
erroneous broadening parameters. |
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