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.

A NE–SW-trending graben at Kap Dalton on the Blosseville Kyst contains an at least 600 m thick succession of Eocene basalt lavas and sediments. The succession has been investigated by new field work, geochemical analysis and radiometric dating by the 40Ar-39Ar incremental heating method. The results show that the volcanic succession comprises about 220 m of the uppermost plateau basalt formation, the Skrænterne Formation. This is separated from the overlying lava flows of the Igtertivâ Formation by 7 m of sediments that represent a period of around six million years. The two formations can be distinguished by different trace element ratios. The Igtertivâ Formation comprises an at least 300 m thick main succession of flows dated to 49.09 ± 0.48 Ma, overlain by sediments of the Bopladsdalen Formation. A basal conglomerate in the sediments contains pebbles of alkaline igneous rocks of which three were dated at 49.17 ± 0.35 Ma, 47.60 ± 0.25 Ma, and 46.98 ± 0.24 Ma. The sediments are thus younger than 47 Ma. Above 30 m of sediments occur two Igtertivâ Formation lava flows dated to 43.77 ± 1.08 Ma. The overlying sediments of the Bopladsdalen and Krabbedalen Formations are therefore not older than about 44 Ma and palynological evidence shows that they are also not much younger than this. Use of the Geological Time Scale 2012 has resulted in good agreement between radiometric and palynological ages. The Igtertivâ Formation lava flows were fed from a regional coast-parallel dyke swarm indicating a new rifting episode at 49–44 Ma. This coincides with a major mid-Eocene plate reorganisation event in the North Atlantic and the start of northward-propagation of the Reykjanes Ridge through the continent. The Igtertivâ rift may have been directly instrumental for the initiation of this process.

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.

Digital elevation models (DEM) were generated from oblique stereo-images acquired with a handheld digital camera. Two model scenarios are considered. Firstly, at local outcrop scale, with easy access, and distances between camera and outcrop varying between c. 40 m and c. 120 m, a very dense and high resolution point cloud was produced. The quality of the point cloud was evaluated against a terrestrial laser scan derived model of the same outcrop. The deviation between the two datasets varies between 0.02 m and 0.09. This is negligible for most geological purposes and illustrates the potential of using terrestrial photogrammetry at local outcrop scale as an alternative to lidar generated elevation data. Secondly, the method is explored at a regional scale, where a set of oblique stereo-images of a remotely located steep inaccessible mountain cliff was collected from a helicopter at a distance of c. 2-5 km under challenging and unfavourable conditions. The quality of the point cloud was evaluated against two elevation models extracted from conventional aerial photographs. Compared to a DEM extracted from monochrome aerial photographs, such as are often the only available topographic source for remote regions, a clear improvement in resolution is observed. Comparison with a DEM extracted from high resolution coloured aerial photographs shows the two digital elevation models to be very similar in resolution and with root mean square deviation (RMSE of 6.0 m).