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| Titel |
Multichannel analysis of correlation length of SEVIRI images around ground-based cloud observatories to determine their representativeness |
| VerfasserIn |
J. Slobodda, A. Hünerbein, R. Lindstrot, R. Preusker, K. Ebell, J. Fischer |
| 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 ; 8, no. 2 ; Nr. 8, no. 2 (2015-02-04), S.567-578 |
| Datensatznummer |
250116121
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| Publikation (Nr.) |
 copernicus.org/amt-8-567-2015.pdf |
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| Zusammenfassung |
Images of measured radiance in different channels of the geostationary
Meteosat-9 SEVIRI instrument are analysed with respect to the
representativeness of the observations of eight cloud observatories in Europe
(e.g. measurements from cloud radars or microwave radiometers). Cloudy
situations are selected to get a time series for every pixel in a
300 km × 300 km area centred around each
ground station. Then a cross correlation of each time series to the pixel
nearest to the corresponding ground site is calculated. In the end a
correlation length is calculated to define the representativeness.
It is found that measurements in the visible and near infrared channels,
which respond to cloud physical properties, are correlated in an area with a
1 to 4 km radius, while the thermal channels, that correspond
to cloud top temperature, are correlated to a distance of about
20 km. This also points to a higher variability of the cloud
microphysical properties inside a cloud than of the cloud top temperature.
The correlation length even increases for the channels at 6.2,
7.3 and 9.7 μm. They respond to
radiation from the upper atmospheric layers emitted by atmospheric gases and
higher level clouds, which are more homogeneous than low-level clouds.
Additionally, correlations at different distances, corresponding to the grid
box sizes of forecast models, were compared. The results suggest the
possibility of comparisons between instantaneous cloud observations from
ground sites and regional forecast models and ground-based measurements. For
larger distances typical for global models the correlations decrease,
especially for short-wave measurements and corresponding cloud products. By
comparing daily means, the correlation length of each station is increased to
about 3 to 10 times the value of instantaneous measurements and also the
comparability to models grows. |
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