Correcting laser scanning intensity recorded in a cave environment for high-resolution lithological mapping: A case study of the Gouffre Georges, France

• Published in: Remote sensing of environment 2022-10, Vol.280, p.113210, Article 113210
• Main Authors: Nováková, Michaela, Gallay, Michal, Šupinský, Jozef, Ferré, Eric, Asti, Riccardo, de Saint Blanquat, Michel, Bajolet, Flora, Sorriaux, Patrick
• Format: Article
• Language: English
• Subjects: Applied geology; Cave; Earth Sciences; Geomorphology; Intensity correction; LiDAR; Lithological mapping; Sciences of the Universe; Terrestrial laser scanning
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2022.113210

Active remote sensing by laser scanning (LiDAR) has markedly improved the mapping of a cave environment with an unprecedented level of accuracy and spatial detail. However, the use of laser intensity simultaneously recorded during the scanning of caves remains unexplored despite it having promising potential for lithological mapping as it has been demonstrated by many applications in open-sky conditions. The appropriate use of laser intensity requires calibration and corrections for influencing factors, which are different in caves as opposed to the above-ground environments. Our study presents an efficient and complex workflow to correct the recorded intensity, which takes into consideration the acquisition geometry, micromorphology of the cave surface, and the specific atmospheric influence previously neglected in terrestrial laser scanning. The applicability of the approach is demonstrated on terrestrial LiDAR data acquired in the Gouffre Georges, a cave located in the northern Pyrenees in France. The cave is unique for its geology and lithology allowing for observation, with a spectacular continuity without any vegetal cover, of the contact between marble and lherzolite rocks and tectonic structures that characterize such contact. The overall accuracy of rock surface classification based on the corrected laser intensity was over 84%. The presence of water or a wet surface introduced bias of the intensity values towards lower values complicating the material discrimination. Such conditions have to be considered in applications of the recorded laser intensity in mapping underground spaces. The presented method allows for putting geological observations in an absolute spatial reference frame, which is often very difficult in a cave environment. Thus, laser scanning of the cave geometry assigned with the corrected laser intensity is an invaluable tool to unravel the complexity of such a lithological environment. •Complex intensity correction workflow for a cave environment was presented.•Atmospheric attenuation needs to be considered for cave-related intensity correction.•Method was efficiently applied to distinguish rock types within the point cloud.•Laser intensity is valuable for detailed mapping of underground environment.