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| Titel |
Determination of circumsolar radiation from Meteosat Second Generation |
| VerfasserIn |
B. Reinhardt, R. Buras, L. Bugliaro, S. Wilbert, B. Mayer |
| 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 ; 7, no. 3 ; Nr. 7, no. 3 (2014-03-31), S.823-838 |
| Datensatznummer |
250115650
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| Publikation (Nr.) |
 copernicus.org/amt-7-823-2014.pdf |
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| Zusammenfassung |
Reliable data on circumsolar radiation, which is caused by
scattering of sunlight by cloud or aerosol particles, is becoming
more and more important for the resource assessment and design of
concentrating solar technologies (CSTs). However, measuring
circumsolar radiation is demanding and only very limited data sets
are available. As a step to bridge this gap,
a method was developed which allows for determination of circumsolar radiation from cirrus cloud
properties retrieved by the geostationary satellites of the Meteosat
Second Generation (MSG) family. The method takes output from the
COCS algorithm to generate a cirrus mask from MSG data and then uses
the retrieval algorithm APICS to obtain the optical thickness and
the effective radius of the detected cirrus, which in turn are used
to determine the circumsolar radiation from a pre-calculated look-up
table. The look-up table was generated from extensive calculations
using a specifically adjusted version of the Monte Carlo radiative
transfer model MYSTIC and by developing a fast yet precise
parameterization. APICS was also improved such that it determines
the surface albedo, which is needed for the cloud property
retrieval, in a self-consistent way instead of using external
data. Furthermore, it was extended to consider new ice particle
shapes to allow for an uncertainty analysis concerning this
parameter.
We found that the nescience of the ice particle shape leads to an
uncertainty of up to 50%. A validation with 1 yr of ground-based
measurements shows, however, that the frequency
distribution of the circumsolar radiation can be
well characterized with typical ice particle
shape mixtures, which feature either smooth or severely roughened
particle surfaces. However, when comparing instantaneous values, timing and
amplitude errors become evident.
For the circumsolar ratio (CSR) this is reflected in a mean
absolute deviation (MAD) of 0.11 for both employed particle shape
mixtures, and a bias of 4 and 11%, for the mixture with smooth and roughend particles, respectively.
If measurements with sub-scale cumulus clouds within the relevant satellite pixels are
manually excluded, the instantaneous agreement between satellite and
ground measurements improves. For a 2-monthly time series, for
which a manual screening of all-sky images was performed, MAD values of 0.08 and 0.07 were obtained for the two employed ice particle mixtures, respectively. |
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