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| Titel |
Sensitivity of remotely sensed trace gas concentrations to polarisation |
| VerfasserIn |
D. M. O'Brien, I. N. Polonsky, J. B. Kumer |
| 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 ; 8, no. 11 ; Nr. 8, no. 11 (2015-11-23), S.4917-4930 |
| Datensatznummer |
250116692
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| Publikation (Nr.) |
 copernicus.org/amt-8-4917-2015.pdf |
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| Zusammenfassung |
| Current and proposed space missions estimate column-averaged
concentrations of trace gases (CO2, CH4 and CO) from high
resolution spectra of reflected sunlight in absorption bands of the gases.
The radiance leaving the top of the atmosphere is partially polarised by both
reflection at the surface and scattering within the atmosphere. Generally, the
polarisation state is unknown and could degrade the accuracy of the
concentration measurements. The sensitivity to polarisation is modelled for
the proposed geoCARB instrument, which will include neither polarisers nor
polarisation scramblers to select particular polarisation states from the
incident radiation. The radiometric and polarimetric calibrations proposed
for geoCARB are outlined, and a model is developed for the polarisation
properties of the geoCARB spectrographs. This model depends principally upon
the efficiencies of the gratings to polarisations parallel and perpendicular
to the rulings of the gratings. Next, an ensemble of polarised spectra is
simulated for geoCARB observing targets in India, China and Australia from
geostationary orbit at longitude 110° E. The spectra are
analysed to recover the trace gas concentrations in two modes, the first
denied access to the polarimetric calibration and the second with access. The
retrieved concentrations using the calibration data are almost identical to
those that would be obtained with polarisation scramblers, while the
retrievals without calibration data contain outliers that do not meet the
accuracies demanded by the mission. |
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