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| Titel |
Speeding up the aerosol optical thickness retrieval using analytical solutions of radiative transfer theory |
| VerfasserIn |
I. L. Katsev, A. S. Prikhach, E. P. Zege, J. O. Grudo, A. A. Kokhanovsky |
| 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 (2010-10-12), S.1403-1422 |
| Datensatznummer |
250001300
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| Publikation (Nr.) |
 copernicus.org/amt-3-1403-2010.pdf |
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| Zusammenfassung |
We present here the aerosol retrieval technique FAR that uses
radiative transfer computations in the process of retrieval rather
than look-up tables (LUT). This approach provides operational
satellite data processing due to the use of the accurate and
extremely fast radiative transfer code RAY previously developed by
authors along with approximate analytical solutions of the radiative
transfer theory. The model of the stratified atmosphere is taken as
two coupled layers. Both layers include aerosol scattering and
absorption, molecular scattering and gas absorption. The atmosphere
parameters are assumed to change from pixel to pixel in the lower
atmosphere layer, but the upper stratified layer of the atmosphere
over 2–3 km is supposed to be horizontally homogenous for the
frame under retrieval. The model of the land spectral albedo is
taken as a weighted sum of two a priory chosen basic spectra.
The aerosol optical thickness (AOT), Angström exponent and the
weight in the land spectral albedo are optimized in the iteration
process using the least-squares technique with fast computations of
the derivatives of radiative characteristics with respect to
retrieved values. The aerosol model and, hence, the aerosol phase
function and single scattering albedo, is predefined and does not
change in the iteration process. The presented version of FAR is
adjusted to process the MERIS data. But it is important that the
developed technique can be adapted for processing data of various
satellite instruments (including any spectral multi-angle
polarization-sensitive sensors).
The use of approximate analytical radiative transfer solutions
considerably speeds up data processing but may lead to about
15–20% increase of AOT retrieval errors. This approach is
advantageous when just the satellite data processing time rather
than high accuracy of the AOT retrieval is crucial. A good example
is monitoring the trans-boundary transfer of aerosol impurities,
particularly in the case of emergencies such as volcano eruptions,
or various industrial disasters.
Beside, two important problems that determine the accuracy of the
AOT retrieval are considered. The first one is the effect of the
preliminary choice of the aerosol model, particularly for the
retrieval from satellite instruments providing only spectral data
(MERIS, MODIS). The second problem is the influence of clouds in
adjacent pixels. As for our knowledge, this problem has not been
given the required attention up to now and it should be properly
accounted for in the AOT retrieval algorithms. |
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