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| Titel |
What do satellite backscatter ultraviolet and visible spectrometers see over snow and ice? A study of clouds and ozone using the A-train |
| VerfasserIn |
A. P. Vasilkov, J. Joiner, D. Haffner, P. K. Bhartia, R. J. D. Spurr |
| 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 ; 3, no. 3 ; Nr. 3, no. 3 (2010-05-18), S.619-629 |
| Datensatznummer |
250001110
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| Publikation (Nr.) |
 copernicus.org/amt-3-619-2010.pdf |
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| Zusammenfassung |
In this paper, we examine how clouds over snow and ice affect ozone
absorption and how these effects may be accounted for in satellite
retrieval algorithms. Over snow and ice, the Aura Ozone Monitoring
Instrument (OMI) Raman cloud pressure algorithm derives an effective
scene pressure. When this scene pressure differs appreciably from the
surface pressure, the difference is assumed to be caused by a cloud
that is shielding atmospheric absorption and scattering below
cloud-top from satellite view. A pressure difference of 100 hPa is
used as a crude threshold for the detection of clouds that
significantly shield tropospheric ozone absorption. Combining the OMI
effective scene pressure and the Aqua MODerate-resolution Imaging
Spectroradiometer (MODIS) cloud top pressure, we can distinguish
between shielding and non-shielding clouds.
To evaluate this approach, we performed radiative transfer simulations
under various observing conditions. Using cloud vertical extinction
profiles from the CloudSat Cloud Profiling Radar (CPR), we find that
clouds over a bright surface can produce significant shielding (i.e.,
a reduction in the sensitivity of the top-of-the-atmosphere radiance
to ozone absorption below the clouds). The amount of shielding
provided by clouds depends upon the geometry (solar and satellite
zenith angles) and the surface albedo as well as cloud optical
thickness. We also use CloudSat observations to qualitatively
evaluate our approach. The CloudSat, Aqua, and Aura satellites fly in
an afternoon polar orbit constellation with ground overpass times
within 15 min of each other.
The current Total Ozone Mapping Spectrometer (TOMS) total column ozone
algorithm (that has also been applied to the OMI) assumes no clouds
over snow and ice. This assumption leads to errors in the retrieved
ozone column. We show that the use of OMI effective scene pressures
over snow and ice reduces these errors and leads to a more homogeneous
spatial distribution of the retrieved total ozone. |
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