Integration of ground-based hyperspectral and lidar scanning in virtual outcrop geology

The potential to visualize and analyse geological outcrops in a 3D environment has made terrestrial laser scanning (TLS) a standard method in geological field studies. Lidar models can be integrated with high resolution photographs to generate photorealistic 3D models, also referred to as virtual outcrop models (VOMs) in geological applications. However, the extraction of mineralogy and geochemical variations from VOMs is limited to the visible light of the photographs and to the single spectral band provided by the laser sensor. Imaging spectrometry applied from airborne and spaceborne platforms is an established method for the regional mapping of mineralogy and lithology, utilising the interaction of solar radiation with the Earth’s surface. Many minerals and rocks can be mapped and analysed in a non-contact manner by utilizing their diagnostic absorption properties within the visible and particularly within the infrared spectral range. The aim of this research is to apply imaging spectrometry with a ground-based instrument to enable mineralogical and lithological analysis of near-vertical outcrop sections. The terms ground-based and close-range are used to indicate a nearhorizontal setup, as opposed to the nadir view found in airborne and spaceborne applications. A workflow has been developed to integrate hyperspectral classifications with 3D lidar models, to compliment VOMs with reliable information about the mineralogy and geochemical variations in the outcrop. The workflow includes data acquisition, spectral and photogrammetric processing of the hyperspectral images, data integration and classifying VOMs utilising hyperspectral image products. A newly developed hyperspectral imager designed as a compact and lightweight instrument, and therefore practical for field applications, has been used. The HySpex SWIR-320m sensor operates within the short wave infrared light (SWIR) with a spectral range between 1.3-2.5 μm. The spectral data were processed with methods primarily developed for airborne and spaceborne applications. All images showed a significant amount of image artefacts, mainly related to the irregular illumination-viewing geometry and bad pixels. While image nonuniformities such as bad pixels are a common problem in pushbroom scanning, other artefacts such as intensity gradients in along-track direction are exacerbated by the close-range scanning and panoramic image geometry. Applying different nonuniformity corrections, image artefacts were m