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| Titel |
Validation of a modified AVHRR aerosol optical depth retrieval algorithm over Central Europe |
| VerfasserIn |
M. Riffler, C. Popp, Armin Hauser, F. Fontana, S. Wunderle |
| 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 ; 3, no. 5 ; Nr. 3, no. 5 (2010-09-20), S.1255-1270 |
| Datensatznummer |
250001290
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| Publikation (Nr.) |
 copernicus.org/amt-3-1255-2010.pdf |
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| Zusammenfassung |
| The Advanced Very High Resolution Radiometer (AVHRR) carried on board
the National Oceanic and Atmospheric Administration (NOAA) and the
Meteorological Operational Satellite (MetOp) polar orbiting satellites
is the only instrument offering more than 25 years of satellite data
to analyse aerosols on a daily basis. The present study assessed
a modified AVHRR aerosol optical depth τa retrieval over
land for Europe. The algorithm might also be applied to other parts of
the world with similar surface characteristics like Europe, only the
aerosol properties would have to be adapted to a new region. The initial
approach used a relationship between Sun photometer measurements from the
Aerosol Robotic Network (AERONET) and the satellite data to post-process
the retrieved τa. Herein a quasi-stand-alone procedure, which
is more suitable for the pre-AERONET era, is presented. In addition, the
estimation of surface reflectance, the aerosol model, and other processing
steps have been adapted. The method's cross-platform applicability was
tested by validating τa from NOAA-17 and NOAA-18 AVHRR at
15 AERONET sites in Central Europe (40.5° N–50° N,
0° E–17° E) from August
2005 to December 2007. Furthermore, the accuracy of the AVHRR retrieval
was related to products from two newer instruments, the Medium Resolution
Imaging Spectrometer (MERIS) on board the Environmental Satellite
(ENVISAT) and the Moderate Resolution Imaging
Spectroradiometer (MODIS) on board Aqua/Terra. Considering the linear
correlation coefficient R, the AVHRR results were similar to
those of MERIS with even lower root mean square error
RMSE. Not surprisingly, MODIS, with its high spectral
coverage, gave the highest R and lowest RMSE.
Regarding monthly averaged τa, the results were
ambiguous. Focusing on small-scale structures, R was reduced
for all sensors, whereas the RMSE solely for MERIS
substantially increased. Regarding larger areas like Central Europe,
the error statistics were similar to the individual match-ups. This
was mainly explained with sampling issues. With the successful
validation of AVHRR we are now able to concentrate on our large data
archive dating back to 1985. This is a unique opportunity for both
climate and air pollution studies over land surfaces. |
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