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| Titel |
Global evaluation of the Collection 5 MODIS dark-target aerosol products over land |
| VerfasserIn |
R. C. Levy, L. A. Remer, R. G. Kleidman, S. Mattoo, C. Ichoku, R. Kahn, T. F. Eck |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 21 ; Nr. 10, no. 21 (2010-11-05), S.10399-10420 |
| Datensatznummer |
250008874
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| Publikation (Nr.) |
 copernicus.org/acp-10-10399-2010.pdf |
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| Zusammenfassung |
| NASA's MODIS sensors have been observing the Earth from polar orbit, from
Terra since early 2000 and from Aqua since mid 2002. We have applied a consistent
retrieval and processing algorithm to both sensors to derive the Collection
5 (C005) dark-target aerosol products over land. Here, we validate the MODIS
along-orbit Level 2 products by comparing to quality assured Level 2 AERONET
sunphotometer measurements at over 300 sites. From 85 463 collocations,
representing mutually cloud-free conditions, we find that >66% (one
standard deviation) of MODIS-retrieved aerosol optical depth (AOD) values
compare to AERONET-observed values within an expected error (EE) envelope
of ±(0.05 + 15%), with high correlation (R = 0.9). Thus, the
MODIS AOD product is validated and quantitative. However, even though we can define EEs for MODIS-reported
Ångström exponent and fine AOD over land, these products do not have similar physical validity. Although validated
globally, MODIS-retrieved AOD does not fall within the EE envelope
everywhere. We characterize some of the residual biases that are related to
specific aerosol conditions, observation geometry, and/or surface
properties, and relate them to situations where particular MODIS algorithm
assumptions are violated. Both Terra's and Aqua's–retrieved AOD are
similarly comparable to AERONET, however, Terra's global AOD bias changes
with time, overestimating (by ~0.005) before 2004, and underestimating
by similar magnitude after. This suggests how small calibration
uncertainties of <2% can lead to spurious conclusions about long-term
aerosol trends. |
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