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Determination of complex refractive indices and optical properties of volcanic ashes in the thermal infrared based on generic petrological compositions

Piontek, Dennis and Hornby, Adrian J. and Voigt, Christiane and Bugliaro Goggia, Luca and Gasteiger, Josef (2021) Determination of complex refractive indices and optical properties of volcanic ashes in the thermal infrared based on generic petrological compositions. Journal of Volcanology and Geothermal Research, p. 107174. Elsevier. doi: 10.1016/j.jvolgeores.2021.107174. ISSN 0377-0273.

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Official URL: https://www.sciencedirect.com/science/article/pii/S0377027321000032

Abstract

The spaceborne detection of volcanic ash clouds at infrared wavelengths helps to avoid regions with enhanced volcanic ash concentrations that pose a threat to aviation. Current volcanic ash data retrievals require detailed information on microphysical properties and the refractive index of volcanic ash, which are highly variable. Uncertainties in the latter currently limit the quality of volcanic ash nowcasts. Here, we introduce a novel method to calculate the complex refractive indices of volcanic ashes at wavelengths from 5 to 15 μm from measurements of their individual components based on generic petrological ash compositions. Thereby the refractive indices for volcanic glasses and bulk volcanic ashes of different chemical compositions are derived. The variability of the latter is mainly influenced by the silica content and the porosity and to a minor degree by the glass-to-crystals ratio. Calculating optical properties exhibits an equally large impact of bulk composition and grain size distribution, whereas particle shape is considered less important for particle sizes of the order 1 μm. Using these optical properties to determine brightness temperature differences between the 11 μm and 12 μm channels we show that the effect of ash composition is non-negligible for modern satellite instruments. Particularly, the dependence of the volcanic ash on the silica content (and to a much smaller extent on the glass-to-crystals ratio) is observable in its refractive index, its optical properties and the brightness temperature difference, indicating that composition might be retrievable to some degree by remote sensing methods.

Item URL in elib:https://elib.dlr.de/135760/
Document Type:Article
Title:Determination of complex refractive indices and optical properties of volcanic ashes in the thermal infrared based on generic petrological compositions
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Piontek, DennisDLR, IPAUNSPECIFIED
Hornby, Adrian J.adrian.hornby (at) min.uni-muenchen.deUNSPECIFIED
Voigt, ChristianeDLR, IPAhttps://orcid.org/0000-0001-8925-7731
Bugliaro Goggia, LucaDLR, IPAhttps://orcid.org/0000-0003-4793-0101
Gasteiger, Josefjosef.gasteiger (at) univie.ac.atUNSPECIFIED
Date:9 January 2021
Journal or Publication Title:Journal of Volcanology and Geothermal Research
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
DOI :10.1016/j.jvolgeores.2021.107174
Page Range:p. 107174
Publisher:Elsevier
ISSN:0377-0273
Status:Published
Keywords:Volcanic Ash, Refractive Index, Optical Properties, Remote Sensing, Thermal Infrared
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:other
DLR - Research area:Aeronautics
DLR - Program:L - no assignment
DLR - Research theme (Project):L - no assignment
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Cloud Physics
Deposited By: Piontek, Dennis
Deposited On:14 Oct 2021 07:53
Last Modified:14 Oct 2021 07:53

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