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| Titel |
APOLLO_NG – a probabilistic interpretation of the APOLLO legacy for AVHRR heritage channels |
| VerfasserIn |
L. Klüser, N. Killius, G. Gesell |
| 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. 10 ; Nr. 8, no. 10 (2015-10-12), S.4155-4170 |
| Datensatznummer |
250116631
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| Publikation (Nr.) |
 copernicus.org/amt-8-4155-2015.pdf |
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| Zusammenfassung |
| The cloud processing scheme APOLLO (AVHRR Processing scheme Over cLouds,
Land and Ocean) has been in use for cloud detection and cloud property
retrieval since the late 1980s. The physics of the APOLLO scheme still build
the backbone of a range of cloud detection algorithms for AVHRR (Advanced
Very High Resolution Radiometer) heritage instruments. The
APOLLO_NG (APOLLO_NextGeneration) cloud
processing scheme is a probabilistic interpretation of the original APOLLO
method. It builds upon the physical principles that have served well in the
original APOLLO scheme. Nevertheless, a couple of additional variables have
been introduced in APOLLO_NG. Cloud detection is no longer
performed as a binary yes/no decision based on these physical principles. It
is rather expressed as cloud probability for each satellite pixel.
Consequently, the outcome of the algorithm can be tuned from being sure to
reliably identify clear pixels to conditions of reliably identifying
definitely cloudy pixels, depending on the purpose. The probabilistic
approach allows retrieving not only the cloud properties (optical depth,
effective radius, cloud top temperature and cloud water path) but also their
uncertainties. APOLLO_NG is designed as a standalone cloud
retrieval method robust enough for operational near-realtime use and for
application to large amounts of historical satellite data. The radiative
transfer solution is approximated by the same two-stream approach which also
had been used for the original APOLLO. This allows the algorithm to be
applied to a wide range of sensors without the necessity of sensor-specific
tuning. Moreover it allows for online calculation of the radiative transfer
(i.e., within the retrieval algorithm) giving rise to a detailed
probabilistic treatment of cloud variables. This study presents the
algorithm for cloud detection and cloud property retrieval together with the
physical principles from the APOLLO legacy it is based on. Furthermore a
couple of example results from NOAA-18 are presented. |
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