OBLIQUE HELICOPTER-BASED LASER SCANNING FOR DIGITAL TERRAIN MODELLING AND VISUALISATION OF GEOLOGICAL OUTCROPS

摘要

Terrestrial laser scanning is becoming increasingly popular for modelling geological outcrops, because of the high resolution, accuracy and ease of dataset integration. Despite these significant advantages, limitations with the technique remain when the spatial extent of the study area is large, as most current systems have a maximum range of less than one kilometre. This becomes a major problem when outcrops are high, as the scanner cannot be positioned far enough away to provide a good angle of view, making data quality poor. This paper reports on a novel use of lidar in geological outcrop modelling, using a helicopter-based system that can be mounted obliquely to allow steep and vertical cliffs to be captured from an optimal scan angle. Use of a helicopter-based system results in large amounts of data, because of the very large areas, which are difficult to process and visualise using available software. In particular, building a 3D mesh from the raw point data, and performing texturing mapping, using a high enough resolution to be able to accurately interpret geology, is difficult. Multiresohitton modelling and specialised viewing software was therefore required to process the 3D data into separate levels of detail and create the texture mapped virtual outcrop model. Despite the targe volumes of data, the processing workflow presented here allowed textured models with tens of kilometres extent to be loaded simultaneously for interpretation and visualisation by geologists, as well as for integration with geophysical data. The use of the helicopter-based Hdar and camera system allowed otherwise inaccessible outcrops in a harsh environment to be studied, with higher quality output than previously possible.