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| Titel |
The influence of polarization on box air mass factors for UV/vis nadir satellite observations |
| VerfasserIn |
Andreas Hilboll, Andreas Richter, Vladimir V. Rozanov, John P. Burrows |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106910
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| Publikation (Nr.) |
 EGU/EGU2015-6592.pdf |
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| Zusammenfassung |
| Tropospheric abundances of pollutant trace gases like, e.g., NO$_{\text{2}}$, are
often derived by applying the differential optical absorption
spectroscopy (DOAS) method to space-borne measurements of
back-scattered and reflected solar radiation. The resulting quantity,
the slant column density (SCD), subsequently has to be converted to
more easily interpretable vertical column densities by means of the
so-called box air mass factor (BAMF). The BAMF describes the ratio of
SCD and VCD within one atmospheric layer and is calculated by a
radiative transfer model.
Current operational and scientific data products of satellite-derived
trace gas VCDs do not include the effect of polarization in their
radiative transfer models. However, the various scattering processes
in the atmosphere do lead to a distinctive polarization pattern of the
observed Earthshine spectra.
This study investigates the influence of these polarization patterns
on box air mass factors for satellite nadir DOAS measurements of NO$_{\text{2}}$
in the UV/vis wavelength region. NO$_{\text{2}}$ BAMFs have been simulated for a
multitude of viewing geometries, surface albedos, and surface
altitudes, using the radiative transfer model SCIATRAN. The results
show a potentially large influence of polarization on the BAMF, which
can reach 10\% and more close to the surface. A simple correction for
this effect seems not to be feasible, as it strongly depends on the
specific measurement scenario and can lead to both high and low biases
of the resulting NO$_{\text{2}}$ VCD. We therefore conclude that all data
products of NO$_{\text{2}}$ VCDs derived from space-borne DOAS measurements
should include polarization effects in their radiative transfer model
calculations, or at least include the errors introduced by using
linear models in their uncertainty estimates. |
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