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| Titel |
A fast SEVIRI simulator for quantifying retrieval uncertainties in the CM SAF cloud physical property algorithm |
| VerfasserIn |
B. J. Jonkheid, R. A. Roebeling, E. Meijgaard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 12, no. 22 ; Nr. 12, no. 22 (2012-11-20), S.10957-10969 |
| Datensatznummer |
250011609
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| Publikation (Nr.) |
 copernicus.org/acp-12-10957-2012.pdf |
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| Zusammenfassung |
The uncertainties in the cloud physical properties derived from
satellite observations make it difficult to interpret
model evaluation studies. In this paper, the uncertainties in the
cloud water path (CWP) retrievals derived with the cloud physical properties
retrieval algorithm (CPP) of the climate monitoring satellite
application facility (CM SAF) are investigated. To this end, a
numerical simulator of MSG-SEVIRI observations has been developed that
calculates the reflectances at 0.64 and 1.63 μm for a wide
range of cloud parameter values, satellite viewing geometries and surface
albedos using a plane-parallel radiative transfer model. The
reflectances thus obtained are used as input to CPP, and the
retrieved values of CWP are compared to the original input of the
simulator. Cloud parameters considered in this paper refer to e.g.
sub-pixel broken clouds and the simultaneous occurrence of ice and
liquid water clouds within one pixel. These configurations are not
represented in the CPP algorithm and as such the associated
retrieval uncertainties are potentially substantial.
It is shown that the CWP retrievals are very sensitive to the
assumptions made in the CPP code. The CWP retrieval errors are
generally small for unbroken single-layer clouds with COT > 10, with
retrieval errors of ~3% for liquid water clouds to ~10% for
ice clouds. In a multi-layer cloud, when both liquid water and ice
clouds are present in a pixel,
the CWP retrieval errors increase dramatically; depending on the
cloud, this can lead to uncertainties of 40–80%. CWP retrievals
also become more uncertain when the cloud does not cover the entire
pixel, leading to errors of ~50% for cloud fractions of
0.75 and even larger errors for smaller cloud fractions. Thus, the
satellite retrieval of cloud physical properties of broken clouds as
well as multi-layer clouds is
complicated by inherent difficulties, and the proper interpretation of
such retrievals requires extra care. |
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