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| Titel |
Validation and empirical correction of MODIS AOT and AE over ocean |
| VerfasserIn |
N. A. J. Schutgens, M. Nakata, T. Nakajima |
| 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. 9 ; Nr. 6, no. 9 (2013-09-23), S.2455-2475 |
| Datensatznummer |
250085068
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| Publikation (Nr.) |
 copernicus.org/amt-6-2455-2013.pdf |
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| Zusammenfassung |
| We present a validation study of Collection 5 MODIS level 2 Aqua and Terra
AOT (aerosol optical thickness) and AE (Ångström exponent) over ocean by comparison to
coastal and island AERONET (AErosol RObotic NETwork) sites for
the years 2003–2009. We show that MODIS (MODerate-resolution Imaging Spectroradiometer) AOT exhibits significant biases due
to wind speed and cloudiness of the observed scene, while MODIS AE, although
overall unbiased, exhibits less spatial contrast on global scales than the
AERONET observations. The same behaviour can be seen when MODIS AOT is
compared against Maritime Aerosol Network (MAN) data, suggesting that the spatial
coverage of our datasets does not preclude global conclusions. Thus, we
develop empirical correction formulae for MODIS AOT and AE that significantly
improve agreement of MODIS and AERONET observations. We show these correction
formulae to be robust. Finally, we study random errors in the corrected MODIS
AOT and AE and show that they mainly depend on AOT itself, although small
contributions are present due to wind speed and cloud fraction in AOT random
errors and due to AE and cloud fraction in AE random errors. Our analysis
yields significantly higher random AOT errors than the official MODIS error
estimate (0.03 + 0.05 τ), while random AE errors are smaller than
might be expected. This new dataset of bias-corrected MODIS AOT and AE over
ocean is intended for aerosol model validation and assimilation studies, but
also has consequences as a stand-alone observational product. For instance,
the corrected dataset suggests that much less fine mode aerosol is
transported across the Pacific and Atlantic oceans. |
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