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| Titel |
Retrieving aerosol in a cloudy environment: aerosol product availability as a function of spatial resolution |
| VerfasserIn |
L. A. Remer, S. Mattoo, R. C. Levy, A. Heidinger, R. B. Pierce, M. Chin |
| 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 ; 5, no. 7 ; Nr. 5, no. 7 (2012-07-30), S.1823-1840 |
| Datensatznummer |
250003018
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| Publikation (Nr.) |
 copernicus.org/amt-5-1823-2012.pdf |
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| Zusammenfassung |
| The challenge of using satellite observations to retrieve aerosol properties
in a cloudy environment is to prevent contamination of the aerosol signal
from clouds, while maintaining sufficient aerosol product yield to satisfy
specific applications. We investigate aerosol retrieval availability at
different instrument pixel resolutions using the standard MODIS aerosol
cloud mask applied to MODIS data and supplemented with a new GOES-R cloud mask
applied to GOES data for a domain covering North America and surrounding
oceans. Aerosol product availability is not the same as the cloud free
fraction and takes into account the techniques used in the MODIS algorithm
to avoid clouds, reduce noise and maintain sufficient numbers of aerosol
retrievals. The inherent spatial resolution of each instrument, 0.5×0.5 km
for MODIS and 1×1 km for GOES, is systematically degraded to 1×1, 2×2,
1×4, 4×4 and 8×8 km resolutions and then analyzed as to how that
degradation would affect the availability of an aerosol retrieval, assuming
an aerosol product resolution at 8×8 km. The analysis is repeated,
separately, for near-nadir pixels and those at larger view angles to
investigate the effect of pixel growth at oblique angles on aerosol
retrieval availability. The results show that as nominal pixel size
increases, availability decreases until at 8×8 km 70% to 85% of the
retrievals available at 0.5 km, nadir, have been lost. The effect at oblique
angles is to further decrease availability over land but increase
availability over ocean, because sun glint is found at near-nadir view
angles. Finer resolution sensors (i.e., 1×1, 2×2 or even 1×4 km) will
retrieve aerosols in partly cloudy scenes significantly more often than
sensors with nadir views of 4×4 km or coarser. Large differences in the
results of the two cloud masks designed for MODIS aerosol and GOES cloud
products strongly reinforce that cloud masks must be
developed with specific purposes in mind and that a generic cloud mask
applied to an independent aerosol retrieval will likely fail. |
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