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| Titel |
Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations |
| VerfasserIn |
P. Liebing, K. Bramstedt, S. Noël, V. Rozanov, H. Bovensmann, J. P. Burrows |
| 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. 6 ; Nr. 6, no. 6 (2013-06-05), S.1503-1520 |
| Datensatznummer |
250017908
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| Publikation (Nr.) |
 copernicus.org/amt-6-1503-2013.pdf |
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| Zusammenfassung |
SCIAMACHY is a passive imaging spectrometer onboard ENVISAT designed to obtain trace gas
abundances from measured radiances and irradiances in the UV to SWIR range in nadir-, limb- and
occultation-viewing modes. Its grating spectrometer introduces a substantial sensitivity to the
polarization of the incoming light with nonnegligible effects on the radiometric calibration. To
be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization
Measurement Devices (PMDs). While for the nadir-viewing mode the measured atmospheric polarization
has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study
regarding the limb-viewing mode has not yet been performed. This paper aims at an assessment of
the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other
air/spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison
with radiative transfer simulations by SCIATRAN V3.1 (Rozanov et al., 2013) using a wide range of
atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable
of performing calculations of the multiply scattered radiance in a spherically symmetric
atmosphere.
The study shows that the limb polarization data exhibit a large time-dependent bias
that decreases with wavelength. Possible reasons for this bias are a still unknown combination of
insufficient accuracy or inconsistencies of the on-ground calibration data, scan mirror
degradation and stress induced changes of the polarization response of components inside the
optical bench of the instrument. It is shown that it should in principle be feasible to
recalibrate the effective polarization sensitivity of the instrument using the in-flight data
and VRTM simulations. |
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