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PhD thesis defense

Sara Salehi, IGN, defends her PhD thesis: Potentials and challenges for hyperspectral mineral mapping in the Arctic

PhD thesis defense — Potentials and challenges for hyperspectral mineral mapping in the Arctic - Developing innovative strategies for data acquisition and integration


Date & Time:

Department of Geosciences and Natural Resource Management (IGN), Øster Voldgade 10, 1350 Copenhagen K. Auditorium C, area 6, ground floor

Hosted by:
Department of Geosciences and Natural Resource Management


Professor Rasmus Fensholt, IGN
Dr. Bjørn Henning Heincke, GEUS

Assessment Committee
Professor Carlos Roberto de Souza Filho, State University of Campinas
Professor Cornelia Glaesser, Martin-Luther-Universität Halle-Wittenberg
Associate Professor Alexander Prishchepov, IGN (chair)

After the PhD defence there will be a reception in Rød Stue, Øster Voldgade 10, Area 6, First floor – everybody is welcome.

Most of the studies using hyperspectral data for geological applications have addressed areas in arid to semi-arid climates. This Ph.D. thesis presents research examining how well geological mapping works under the arctic, high relief conditions of Greenland, using hyperspectral data acquired from different platforms and at various scales. Building upon the results derived from regional airborne hyperspectral data, it is demonstrated that one of the main sources for potential misclassification of pixels in the Arctic is the subpixel spectral mixing of lichens and their rock substrate. The effect of lichens with respect to geological applications is investigated and suitable mapping approaches are proposed for mapping lithology in areas of abundant lichens.

The second major challenge that has been addressed is the lack of feasible approaches to capture the hyperspectral data as part of a large-scale operation in a time- and cost-effective manner, in particular for areas of difficult access. For this reason, a new data acquisition strategy, namely long range terrestrial outcrop sensing is proposed and tested in West and South West Greenland. Despite the promising results achieved by using this approach, the rugged topography and difficult terrain accessibility in the Arctic often hinder the instrumentation setup and limit the employment of such a data acquisition strategy. To overcome these limitations, the potential of using a platform in motion (such as a boat/ship) is investigated to continuously acquire the hyperspectral data while sailing along the fjords. In addition, the two-dimensional maps generated from hyperspectral imaging are transformed to three-dimensional hyperclouds and integrated with terrain models generated from oblique photogrammetry. The high spatial resolution of terrain models allows investigating e.g. faults and the general morphology of lithologies whereas spectral data provides information regarding the mineralogy and chemical composition of the rocks. The observations suggest that regardless of using terrestrial or moving platforms, performing the required preprocessing for data captured from distant targets is not straight-forward. Firstly, the logistical setup of “visible” reference targets for radiometric correction with the same orientation and distance as the distant target outcrop is not possible. Secondly, large distances between the sensor and the outcrop lead to major atmospheric distortions. Thirdly, owing to the large scale of the observed surface and the sensor viewing perspective, pixels within one scene can represent a range of different distances and orientations, leading to highly variable radiometric distortions. For those reasons, correction methods established for nadir acquisitions are modified here to account for the special conditions of long-range sub-horizontal sensing of outcrops.

The thesis is available from the PhD administration office 04.1.417