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| Titel |
Detection of multi-layer and vertically-extended clouds using A-train sensors |
| VerfasserIn |
J. Joiner, A. P. Vasilkov, P. K. Bhartia, G. Wind, S. Platnick, W. P. Menzel |
| 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. 1 ; Nr. 3, no. 1 (2010-02-15), S.233-247 |
| Datensatznummer |
250000825
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| Publikation (Nr.) |
 copernicus.org/amt-3-233-2010.pdf |
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| Zusammenfassung |
The detection of multiple cloud layers using satellite observations is
important for retrieval algorithms as well as climate applications. In
this paper, we describe a relatively simple algorithm to detect
multiple cloud layers and distinguish them from vertically-extended
clouds. The algorithm can be applied to coincident passive sensors
that derive both cloud-top pressure from the thermal infrared
observations and an estimate of solar photon pathlength from UV,
visible, or near-IR measurements. Here, we use data from the A-train
afternoon constellation of satellites: cloud-top pressure, cloud
optical thickness, the multi-layer flag from the Aqua
MODerate-resolution Imaging Spectroradiometer (MODIS) and the optical
centroid cloud pressure from the Aura Ozone Monitoring Instrument
(OMI). For the first time, we use data from the CloudSat radar to
evaluate the results of a multi-layer cloud detection scheme.
The cloud classification algorithms applied with different
passive sensor configurations compare well with each other as well as
with data from CloudSat.
We compute monthly mean fractions of pixels containing multi-layer and
vertically-extended clouds for January and July 2007 at the OMI
spatial resolution (12 km×24 km at nadir) and
at the 5 km×5 km MODIS resolution used for infrared
cloud retrievals. There are seasonal variations in the spatial
distribution of the different cloud types. The fraction of cloudy pixels
containing distinct multi-layer cloud is a strong function of the
pixel size. Globally averaged, these fractions are approximately 20% and
10% for OMI and MODIS, respectively. These fractions may be
significantly higher or lower depending upon location. There is a much
smaller resolution dependence for fractions of pixels containing
vertically-extended clouds (~20% for OMI and slightly less for
MODIS globally), suggesting larger spatial scales for these clouds. We
also find higher fractions of vertically-extended clouds
over land as compared with ocean, particularly in the tropics and
summer hemisphere. |
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