Abstract:Recently, ground-based hyperspectral imaging has come to the fore, supporting the arduous task of mapping near-vertical, difficult-to-access geological outcrops. The application of outcrop sensing within a range of one to several hundred metres, including geometric corrections and integration with accurate terrestrial laser scanning models, is already developing rapidly. However, there are few studies dealing with ground-based imaging of distant targets (i.e., in the range of several kilometres) such as mountain ridges, cliffs, and pit walls. In particular, the extreme influence of atmospheric effects and topography-induced illumination differences have remained an unmet challenge on the spectral data. These effects cannot be corrected by means of common correction tools for nadir satellite or airborne data. Thus, this article presents an adapted workflow to overcome the challenges of long-range outcrop sensing, including straightforward atmospheric and topographic corrections. Using two datasets with different characteristics, we demonstrate the application of the workflow and highlight the importance of the presented corrections for a reliable geological interpretation. The achieved spectral mapping products are integrated with 3D photogrammetric data to create large-scale now-called "hyperclouds", i.e., geometrically correct representations of the hyperspectral datacube. The presented workflow opens up a new range of application possibilities of hyperspectral imagery by significantly enlarging the scale of ground-based measurements.
Abstract. The 17 June 2017 rock avalanche in the Karrat Fjord, West Greenland, caused a
tsunami that flooded the nearby village of Nuugaatsiaq and killed four
people. The disaster was entirely unexpected since no previous records of
large rock slope failures were known in the region, and it highlighted the
need for better knowledge of potentially hazardous rock slopes in remote
Arctic regions. The aim of the paper is to explore our ability to detect and locate unstable
rock slopes in remote Arctic regions with difficult access. We test this by
examining the case of the 17 June 2017 Karrat rock avalanche. The workflow
we apply is based on a multidisciplinary analysis of freely available data
comprising seismological records, Sentinel-1 spaceborne synthetic-aperture
radar (SAR) data, and Landsat and Sentinel-2 optical satellite imagery,
ground-truthed with limited fieldwork. Using this workflow enables us to
reconstruct a timeline of rock slope failures on the coastal slope here
collectively termed the Karrat Landslide Complex. Our analyses show that at least three recent rock avalanches occurred in the
Karrat Landslide Complex: Karrat 2009, Karrat 2016, and Karrat 2017. The
latter is the source of the abovementioned tsunami, whereas the first two
are described here in detail for the first time. All three are interpreted
as having initiated as dip-slope failures. In addition to the recent rock
avalanches, older rock avalanche deposits are observed, demonstrating older
(Holocene) periods of activity. Furthermore, three larger unstable rock
slopes that may pose a future hazard are described. A number of non-tectonic
seismic events confined to the area are interpreted as recording rock slope
failures. The structural setting of the Karrat Landslide Complex, namely
dip slope, is probably the main conditioning factor for the past and present
activity, and, based on the temporal distribution of events in the area, we
speculate that the possible trigger for rock slope failures is permafrost
degradation caused by climate warming. The results of the present work highlight the benefits of a
multidisciplinary approach, based on freely available data, to studying unstable
rock slopes in remote Arctic areas under difficult logistical field
conditions and demonstrate the importance of identifying minor precursor
events to identify areas of future hazard.
The Nuussuaq Basin in West Greenland has an obvious exploration potential. Most of the critical elements are well documented, including structures that could form traps, reservoir rocks, seals and oil and gas seepage that documents petroleum generation. And yet, we still lack a full understanding of the petroleum systems, especially the distribution of mature source rocks in the subsurface and the vertical and lateral migration of petroleum into traps. A recently proposed anticlinal structural model could be very interesting for exploration if evidence of source rocks and migration pathways can be found. In this paper, we review all existing, mostly unpublished, data on gas observations from Nuussuaq. Furthermore, we present new oil and gas seepage data from the vicinity of the anticline. Occurrence of gas within a few kilometres on both sides of the mapped anticline has a strong thermogenic fingerprint, suggesting an origin from oil-prone source rocks with a relatively low thermal maturity. Petroleum was extracted from an oil-stained hyaloclastite sample collected in the Aaffarsuaq valley in 2019, close to the anticline. Biomarker analyses revealed the oil to be a variety of the previously characterised “Niaqornaarsuk type,” reported to be formed from Campanian-age source rocks. Our new analysis places the “Niaqornaarsuk type” 10 km from previously documented occurrences and further supports the existence of Campanian age deposits developed in source rock facies in the region.
M. 2019: Developing multi-sensor drones for geological mapping and mineral exploration: setup and first results from the MULE-DRO project. Geological Survey of Denmark and Greenland Bulletin 43, e2019430302.
Abstract:Remote and extreme regions such as in the Arctic remain a challenging ground for geological mapping and mineral exploration. Coastal cliffs are often the only major well-exposed outcrops, but are mostly not observable by air/spaceborne nadir remote sensing sensors. Current outcrop mapping efforts rely on the interpretation of Terrestrial Laser Scanning and oblique photogrammetry, which have inadequate spectral resolution to allow for detection of subtle lithological differences. This study aims to integrate 3D-photogrammetry with vessel-based hyperspectral imaging to complement geological outcrop models with quantitative information regarding mineral variations and thus enables the differentiation of barren rocks from potential economic ore deposits. We propose an innovative workflow based on: (1) the correction of hyperspectral images by eliminating the distortion effects originating from the periodic movements of the vessel; (2) lithological mapping based on spectral information; and (3) accurate 3D integration of spectral products with photogrammetric terrain data. The method is tested using experimental data acquired from near-vertical cliff sections in two parts of Greenland, in Karrat (Central West) and Søndre Strømfjord (South West). Root-Mean-Square Error of (6.7, 8.4) pixels for Karrat and (3.9, 4.5) pixels for Søndre Strømfjord in X and Y directions demonstrate the geometric accuracy of final 3D products and allow a precise mapping of the targets identified using the hyperspectral data contents. This study highlights the potential of using other operational mobile platforms (e.g., unmanned systems) for regional mineral mapping based on horizontal viewing geometry and multi-source and multi-scale data fusion approaches.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.