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| Titel |
Retrieval of aerosol optical depth over land based on a time series technique using MSG/SEVIRI data |
| VerfasserIn |
L. Mei, Y. Xue, G. Leeuw, T. Holzer-Popp, J. Guang, Y. Li, L. Yang, H. Xu, X. Xu, C. Li, Y. Wang, C. Wu, T. Hou, X. He, J. Liu, J. Dong, Z. Chen |
| 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 ; 12, no. 19 ; Nr. 12, no. 19 (2012-10-10), S.9167-9185 |
| Datensatznummer |
250011500
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| Publikation (Nr.) |
 copernicus.org/acp-12-9167-2012.pdf |
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| Zusammenfassung |
A novel approach for the joint retrieval of aerosol optical depth (AOD) and
aerosol type, using Meteosat Second Generation – Spinning Enhanced Visible
and Infrared Imagers (MSG/SEVIRI) observations in two solar channels, is
presented. The retrieval is based on a Time Series (TS) technique, which
makes use of the two visible bands at 0.6 μm and 0.8 μm
in three orderly scan times (15 min interval between two scans) to retrieve
the AOD over land. Using the radiative transfer equation for plane-parallel
atmosphere, two coupled differential equations for the upward and downward
fluxes are derived. The boundary conditions for the upward and downward
fluxes at the top and at the bottom of the atmosphere are used in these
equations to provide an analytic solution for the AOD. To derive these
fluxes, the aerosol single scattering albedo (SSA) and asymmetry factor are
required to provide a solution. These are provided from a set of six
pre-defined aerosol types with the SSA and asymmetry factor. We assume one aerosol type for a grid of
1°×1° and the surface reflectance changes little
between two subsequent observations. A k-ratio approach is used in the
inversion to find the best solution of atmospheric properties and surface
reflectance. The k-ratio approach assumes that the surface reflectance is
little influenced by aerosol scattering at 1.6 μm and therefore the
ratio of surface reflectances in the solar band for two subsequent
observations can be well-approximated by the ratio of the reflectances at
1.6 μm. A further assumption is that the surface reflectance varies
only slightly over a period of 30 min. The algorithm makes use of
numerical minimisation routines to obtain the optimal solution of atmospheric
properties and surface reflectance by selection of the most suitable aerosol
type from pre-defined sets.
A detailed analysis of the retrieval results shows that it is suitable for
AOD retrieval over land from SEVIRI data. Six AErosol RObotic NETwork (AERONET) sites with different
surface types are used for detailed analysis and 42 other AERONET sites are
used for validation. From 445 collocations representing stable and
homogeneous aerosol type, we find that >75% of the MSG-retrieved AOD at
0.6 and 0.8 μm values compare favourably with AERONET observed
AOD values, within an error envelope of ± 0.05 ± 0.15 τ and a
high correlation coefficient (R>0.86). The AOD datasets derived using the
TS method with SEVIRI data is also compared with collocated AOD products
derived from NASA TERRA and AQUA MODIS (The Moderate-resolution Imaging
Spectroradiometer) data using the Dark Dense Vegetation
(DDV) method and the Deep Blue algorithms. Using the TS method, the AOD could
be retrieved for more pixels than with the NASA Deep Blue algorithm. This
method is potentially also useful for surface reflectance retrieval using
SEVIRI observations. The current paper focuses on AOD retrieval and analysis,
and the analysis and validation of reflectance will be given in a following
paper. |
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