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| Titel |
MISR Dark Water aerosol retrievals: operational algorithm sensitivity to particle non-sphericity |
| VerfasserIn |
O. V. Kalashnikova, M. J. Garay, J. V. Martonchik, D. J. Diner |
| 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 ; 6, no. 8 ; Nr. 6, no. 8 (2013-08-27), S.2131-2154 |
| Datensatznummer |
250085044
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| Publikation (Nr.) |
 copernicus.org/amt-6-2131-2013.pdf |
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| Zusammenfassung |
| The aim of this study is to theoretically investigate the sensitivity of the
Multi-angle Imaging SpectroRadiometer (MISR) operational (version 22) Dark
Water retrieval algorithm to aerosol non-sphericity over the global oceans
under actual observing conditions, accounting for current algorithm
assumptions. Non-spherical (dust) aerosol models, which were introduced in
version 16 of the MISR aerosol product, improved the quality and coverage of
retrievals in dusty regions. Due to the sensitivity of the retrieval to the
presence of non-spherical aerosols, the MISR aerosol product has been
successfully used to track the location and evolution of mineral dust plumes
from the Sahara across the Atlantic, for example. However, the MISR global
non-spherical aerosol optical depth (AOD) fraction product has been found to
have several climatological artifacts superimposed on valid detections of
mineral dust, including high non-spherical fraction in the Southern Ocean and
seasonally variable bands of high non-sphericity. In this paper we introduce
a formal approach to examine the ability of the operational MISR Dark Water
algorithm to distinguish among various spherical and non-spherical particles
as a function of the variable MISR viewing geometry. We demonstrate the
following under the criteria currently implemented: (1) Dark Water retrieval
sensitivity to particle non-sphericity decreases for AOD below about 0.1
primarily due to an unnecessarily large lower bound imposed on the
uncertainty in MISR observations at low light levels, and improves when this
lower bound is removed; (2) Dark Water retrievals are able to distinguish
between the spherical and non-spherical particles currently used for all MISR
viewing geometries when the AOD exceeds 0.1; (3) the sensitivity of the MISR
retrievals to aerosol non-sphericity varies in a complex way that depends on
the sampling of the scattering phase function and the contribution from
multiple scattering; and (4) non-sphericity artifacts occur at those
view-illumination geometries where dust aerosols are indistinguishable from
certain types of cirrus particles. Based on these results, we suggest that
interested parties use caution with the version 22 MISR Dark Water aerosol
non-sphericity product in situations where cirrus may be present. |
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