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Modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens

Salehi, Sara and Rogge, Derek and Rivard, Benoit and Heincke, Bjørn Henning and Fensholt, Rasmus (2017) Modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens. Remote Sensing of Environment, 199, pp. 78-92. Elsevier. DOI: 10.1016/j.rse.2017.06.044 ISSN 0034-4257

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Official URL: http://www.sciencedirect.com/science/article/pii/S0034425717303036

Abstract

Arctic environments provide a challenging ground for geological mapping and mineral exploration. Inaccessibility complicates ground surveys and the presence of ice, vegetation, and lichens hinders supportive remote sensing surveys. Spectral mixing of lichens and bare rock can shift the wavelength position of characteristic absorption features, thereby complicating the spectral mapping of minerals and lithologies. The extent to which diagnostic rock features are preserved despite the presence of lichens is of major concern in remotely sensed geological studies and estimates of the critical level of lichen coverage, below which spectral features of the mineral substrate can still be identified, are needed. We investigated how surficial lichen cover affects the characteristics of shortwave infrared (SWIR) mineral absorption features and the efficacy of automated absorption feature extraction. For this purpose, mixed spectra were synthetically generated from laboratory spectra of common rock formingSWIR absorbing minerals and lichens.Wavelength displacements of characteristic absorption features for each mixed spectrum were then analyzed as a function of percentage lichen cover. Distinctive trends were identified that can be used in future analysis: The strong spectral features of mica group minerals around 2200 and 2340–2350 nm maintain their integrity for up to 30% lichen cover, despite the related shift toward shorter wavelengths for higher percentage lichen cover. In contrast, very weak absorption bands around 2440 nm in (white) micas spectra are completely obscured for a lichen cover of ≥50%. Our observations suggest that the chlorite feature around 2250 nm is shifted toward longer wavelengths and the depth of this feature as well as the contrast between lichen and substrate spectra define the amount of lichen needed to mask it. Furthermore, lichens induce a spectral shift towards shorter wavelengths for the features around 2320 nm for the rocks containing amphibole, chlorite, carbonate and serpentine group minerals. In addition, no wavelength displacement is observed for chlorite, biotite and phlogopite features around 2380 nmin mixtures with lichens. By quantifying lichen cover effects on mineral absorption features, our study highlights the importance of being precautious in any interpretation in areas characterized by abundant lichen-covered outcrops. This can be of significant importance for mineral and deposit vectoring as the presence of abundant lichen coverage causing slightly shifted features for a given spectra can be erroneously identified as a path to a deposit.

Item URL in elib:https://elib.dlr.de/113260/
Document Type:Article
Title:Modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Salehi, Sarassal (at) geus.dkUNSPECIFIED
Rogge, Derekderek.rogge (at) dlr.deUNSPECIFIED
Rivard, Benoitbenoit.rivard (at) ualberta.caUNSPECIFIED
Heincke, Bjørn Henningbhm (at) geus.dkUNSPECIFIED
Fensholt, Rasmusrf (at) ign.ku.dkUNSPECIFIED
Date:2017
Journal or Publication Title:Remote Sensing of Environment
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:199
DOI :10.1016/j.rse.2017.06.044
Page Range:pp. 78-92
Publisher:Elsevier
ISSN:0034-4257
Status:Published
Keywords:Greenland Hyperspectral remote sensing Lichen cover Mineral exploration Spectral mapping
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Erdbeobachtung
DLR - Research theme (Project):R - Remote sensing and geoscience
Location: Oberpfaffenhofen
Institutes and Institutions:German Remote Sensing Data Center > Land Surface
Deposited By: Rogge, Derek
Deposited On:27 Jul 2017 14:57
Last Modified:11 Jan 2018 10:43

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