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| Titel |
Statistically optimized inversion algorithm for enhanced retrieval of aerosol properties from spectral multi-angle polarimetric satellite observations |
| VerfasserIn |
O. Dubovik, M. Herman, A. Holdak, T. Lapyonok, D. Tanré, J. L. Deuzé, F. Ducos, A. Sinyuk, A. Lopatin |
| 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 ; 4, no. 5 ; Nr. 4, no. 5 (2011-05-31), S.975-1018 |
| Datensatznummer |
250001989
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| Publikation (Nr.) |
 copernicus.org/amt-4-975-2011.pdf |
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| Zusammenfassung |
The proposed development is an attempt to enhance aerosol retrieval by
emphasizing statistical optimization in inversion of advanced satellite
observations. This optimization concept improves retrieval accuracy relying
on the knowledge of measurement error distribution. Efficient application of
such optimization requires pronounced data redundancy (excess of the
measurements number over number of unknowns) that is not common in satellite
observations. The POLDER imager on board the PARASOL micro-satellite
registers spectral polarimetric characteristics of the reflected atmospheric
radiation at up to 16 viewing directions over each observed pixel. The
completeness of such observations is notably higher than for most currently
operating passive satellite aerosol sensors. This provides an opportunity
for profound utilization of statistical optimization principles in satellite
data inversion. The proposed retrieval scheme is designed as statistically
optimized multi-variable fitting of all available angular observations
obtained by the POLDER sensor in the window spectral channels where
absorption by gas is minimal. The total number of such observations by
PARASOL always exceeds a hundred over each pixel and the statistical
optimization concept promises to be efficient even if the algorithm
retrieves several tens of aerosol parameters. Based on this idea, the
proposed algorithm uses a large number of unknowns and is aimed at retrieval
of extended set of parameters affecting measured radiation.
The algorithm is designed to retrieve complete aerosol properties globally.
Over land, the algorithm retrieves the parameters of underlying surface
simultaneously with aerosol. In all situations, the approach is anticipated
to achieve a robust retrieval of complete aerosol properties including
information about aerosol particle sizes, shape, absorption and composition
(refractive index). In order to achieve reliable retrieval from PARASOL
observations even over very reflective desert surfaces, the algorithm was
designed as simultaneous inversion of a large group of pixels within one or
several images. Such multi-pixel retrieval regime takes advantage of known
limitations on spatial and temporal variability in both aerosol and surface
properties. Specifically the variations of the retrieved parameters
horizontally from pixel-to-pixel and/or temporary from day-to-day are
enforced to be smooth by additional a priori constraints. This concept is
expected to provide satellite retrieval of higher consistency, because the
retrieval over each single pixel will be benefiting from coincident aerosol
information from neighboring pixels, as well, from the information about
surface reflectance (over land) obtained in preceding and consequent
observations over the same pixel.
The paper provides in depth description of the proposed inversion concept,
illustrates the algorithm performance by a series of numerical tests and
presents the examples of preliminary retrieval results obtained from actual
PARASOL observations. It should be noted that many aspects of the described
algorithm design considerably benefited from experience accumulated in the
preceding effort on developments of currently operating AERONET and PARASOL
retrievals, as well as several core software components were inherited from
those earlier algorithms. |
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