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| Titel |
Retrieving microphysical properties of dust-like particles using ellipsoids: the case of refractive index |
| VerfasserIn |
O. Kemppinen, T. Nousiainen, S. Merikallio, P. Räisänen |
| 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 ; 15, no. 19 ; Nr. 15, no. 19 (2015-10-06), S.11117-11132 |
| Datensatznummer |
250120080
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| Publikation (Nr.) |
 copernicus.org/acp-15-11117-2015.pdf |
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| Zusammenfassung |
| Distributions of ellipsoids are often used to simulate the optical properties
of non-ellipsoidal atmospheric particles, such as dust. In this work, the
applicability of ellipsoids for retrieving the refractive index of dust-like
target model particles from scattering data is investigated. This is a pure
modeling study, in which stereogrammetrically retrieved model dust shapes are
used as targets. The primary objective is to study whether the refractive
index of these target particles can be inverted from their scattering
matrices using ellipsoidal model particles. To achieve this, first scattering
matrices for the target model particles with known refractive indices are
computed. First, a non-negative least squares fitting is performed,
individually for each scattering matrix element, for 46 differently shaped
ellipsoids by using different assumed refractive indices. Then, the fitting
error is evaluated to establish whether the ellipsoid ensemble best matches
the target scattering matrix elements when the correct refractive index is
assumed. Second, we test whether the ellipsoids best match the target data
with the correct refractive index, when a predefined (uniform) shape
distribution for ellipsoids is assumed, instead of optimizing the shape
distribution separately for each tested refractive index. The results show
not only that for both of these approaches using ellipsoids with the true refractive
index produces good results but also that for each scattering matrix element
even better results are acquired by using wrong refractive indices. In
addition, the best agreement is obtained for different scattering matrix
elements using different refractive indices. The findings imply that
retrieval of refractive index of non-ellipsoidal particles whose
single-scattering properties have been modeled with ellipsoids may not be
reliable. Furthermore, it is demonstrated that the differences in
single-scattering albedo and asymmetry parameter between the best-match
ellipsoid ensemble and the target particles may give rise to major
differences in simulated aerosol radiative effects. |
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