3-D stratigraphic mapping using a digital outcrop model derived from UAV images and structure-from-motion photogrammetry

Abstract

Fluvial deposits are highly heterogeneous and inherently challenging to map in outcrop due to a combination of lateral and vertical variability along with a lack of continuous exposure. Heavily incised landscapes, such as badlands, reveal continuous three-dimensional (3-D) outcrops that are ideal for constraining the geometry of fluvial deposits and enabling reconstruction of channel morphology through time and space. However, these complex 3-D landscapes also create challenges for conventional field mapping techniques, which offer limited spatial resolution, coverage, and/or lateral contiguity of measurements. To address these limitations, we examined an emerging technique using images acquired from a small unmanned aerial vehicle (UAV) and structure-from-motion (SfM) photogrammetric processing to generate a 3-D digital outcrop model (DOM). We applied the UAV-SfM technique to develop a DOM of an Upper Cretaceous channel-belt sequence exposed within a 0.52 km 2 area of Dinosaur Provincial Park (southeastern Alberta, Canada). Using the 3-D DOM, we delineated the lower contact of the channel-belt sequence, created digital sedimentary logs, and estimated facies with similar conviction to field-based estimations (±4.9%). Lateral accretion surfaces were also recognized and digitally traced within the DOM, enabling measurements of accretion direction (dip azimuth), which are nearly impossible to obtain accurately in the field. Overall, we found that measurements and observations derived from the UAV-SfM DOM were commensurate with conventional ground-based mapping techniques, but they had the added advantage of lateral continuity, which aided interpretation of stratigraphic surfaces and facies. This study suggests that UAV-SfM DOMs can complement traditional field-based methods by providing detailed 3-D views of topographically complex outcrop exposures spanning intermediate to large spatial extents.

Analysis of Fracture Roughness Control on Permeability Using SfM and Fluid Flow Simulations: Implications for Carbonate Reservoir Characterization

“…Among these methods, SfM photogrammetry shows great promise as it is inexpensive (photo-camera and processing software) and extremely flexible regarding the scales and conditions (applicable in the field and laboratory). For example, SfM photogrammetry has been successfully used as an analytical tool to gather geologic data from outcrop studies [20][21][22][23], as well as at smaller scales on fault surfaces [19] and fossilized human footprints [24].…”

Visualization and Sharing of 3D Digital Outcrop Models to Promote Open Science

“…Contrasting layers of siltstone and fine-to medium-grained sandstone along with the stratigraphic architecture are representative of successive meandering channel belts cutting through adjacent floodplain mudstones (Figs. 1-2; Smith et al, 2009;Nesbit et al, 2018;Durkin et al, 2020). Most of the park is a natural preserve accessible only through research permits or guided programs.…”

“…Images were recorded at a pitch angle of 10º off-nadir to increase point visibility along sub-vertical surfaces and increase precision of final models within the high-relief topography (Nesbit and Hugenholtz, 2019). Images were processed using Pix4Dmapper v4.3 following a similar workflow described by previous authors (Küng et al, 2012;Nesbit et al, 2018). Following initial processing, the model was divided into four quadrants and processed into a dense point cloud and 3D textured mesh.…”

“…Digital 3D mapping approaches using DOMs have enabled geoscientists to perform supplemental measurements, correlations, and interpretations that are difficult or impossible to obtain with traditional methods (Figs. 1-2; Pavlis and Mason, 2017;Nesbit et al, 2018).…”

“…A number of methods are now available for collecting and processing 3D models (Hodgetts, 2013;Carrivick et al, 2016). In particular, structure-from-motion and multi-view stereo (SfM-MVS) photogrammetry software, commonly paired with uninhabited aerial vehicles (UAVs), enables geoscientists to produce photorealistic DOMs through a highly streamlined UAV-SfM workflow (Chesley et al, 2017;Nieminski and Graham, 2017;Pavlis and Mason, 2017;Nesbit and Hugenholtz, 2019).…”