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| Titel |
A threshold-based cloud mask for the high-resolution visible channel of Meteosat Second Generation SEVIRI |
| VerfasserIn |
S. Bley, H. Deneke |
| 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 ; 6, no. 10 ; Nr. 6, no. 10 (2013-10-18), S.2713-2723 |
| Datensatznummer |
250085085
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| Publikation (Nr.) |
 copernicus.org/amt-6-2713-2013.pdf |
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| Zusammenfassung |
A threshold-based cloud mask for the high-resolution visible
(HRV) channel (1 × 1 km2) of the Meteosat SEVIRI (Spinning
Enhanced Visible and Infrared Imager) instrument is introduced and evaluated. It is based on operational
EUMETSAT cloud mask for the low-resolution channels of SEVIRI
(3 × 3 km2), which is used for the selection of
suitable thresholds to ensure consistency with its results. The aim of
using the HRV channel is to resolve small-scale cloud structures that
cannot be detected by the low-resolution channels. We find that it is
of advantage to apply thresholds relative to clear-sky reflectance
composites, and to adapt the threshold regionally. Furthermore, the
accuracy of the different spectral channels for thresholding and the
suitability of the HRV channel are investigated for cloud
detection. The case studies show different situations to demonstrate
the behavior for various surface and cloud conditions.
Overall, between 4 and 24% of cloudy low-resolution SEVIRI
pixels are found to contain broken clouds in our test data set
depending on considered region. Most of these broken pixels are
classified as cloudy by EUMETSAT's cloud mask, which will likely
result in an overestimate if the mask is used as an estimate of cloud
fraction. The HRV cloud mask aims for small-scale convective
sub-pixel clouds that are missed by the EUMETSAT cloud mask.
The major limit of the HRV cloud mask is the minimum cloud optical
thickness (COT) that can be detected. This threshold COT was found
to be about 0.8 over ocean and 2 over land and is highly related to the
albedo of the underlying surface. |
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