Digital outcrop modelling using "structure-from- motion" photogrammetry: acquisition strategies, validation and interpretations to different sedimentary environments

Abstract

Structure from Motion–Multi-View Stereo (SfM-MVS) is a relatively new technique that is being adopted in the analysis of sedimentary systems. The technique is especially applicable to studies which focus on the distribution, geometry and quantification of geological bodies including the analysis of sedimentary forms and tectonic structures. This photogrammetric method allows for generating virtual outcrops (VO) and high-resolution digital terrain models (DTMs). In comparison with more sophisticated and expensive techniques such as airborne LiDAR scanning or terrestrial laser scanning, SfM-MVS is a fast low-cost method which with careful use of ground control points, can produce models which are comparable to other digital survey methods for spatial accuracy. In this study, the effectiveness of SfM-MVS in a series of quantitative case studies in sedimentary and basin analyses is discussed. Focus is placed on how the research questions define the workflow strategy to know the limitations, sources of error and potential utility that the SFM-MVS technique has when a virtual sedimentary system is interpreted. Three case studies of different sedimentary environments, previously analyzed with traditional fieldwork techniques, were selected and re-analyzed. For each case study the objective was to resolve quantitative questions that were not possible to determine without the use of VO or DTMs. Questions include: (i) geometrical restoration of a growth strata succession associated with thrust systems; (ii) stacking patterns of littoral ridges during a relative sea-level fall after the Holocene climatic optimum; and (iii) quantification of lake level fall during the past 44 years of a closed lake basin. The results of the work show that the technique has significant application in the analysis of sedimentary systems. However, since geological interpretations depend on the quality of the models that are generated, planning and construction of the VO or DEMs along with their validation are essential to ensure reliable results.