Improvement of Workflow for Topographic Surveys in Long Highwalls of Open Pit Mines with an Unmanned Aerial Vehicle and Structure from Motion

Abstract

Conducting topographic surveys in active mines is challenging due ongoing operations and hazards, particularly in highwalls subject to constant and active mass movements (rock and earth falls, slides and flows). These vertical and long surfaces are the core of most mines, as the mineral feeding mining production originates there. They often lack easy and safe access paths. This framework highlights the importance of accomplishing non-contact high-accuracy and detailed topographies to detect instabilities prior to their occurrence. We have conducted drone flights in search of the best settings in terms of altitude mode and camera angle, to produce digital representation of topographies using Structure from Motion. Identification of discontinuities was evaluated, as they are a reliable indicator of potential failure areas. Natural shapes were used as control/check points and were surveyed using a robotic total station with a coaxial camera. The study was conducted in an active kaolin mine near the Alto Tajo Natural Park of East-Central Spain. Here the 140 m highwall is formed by layers of limestone, marls and sands. We demonstrate that for this vertical landscape, a facade drone flight mode combined with a nadir camera angle, and automatically programmed with a computer-based mission planning software, provides the most accurate and detailed topographies, in the shortest time and with increased flight safety. Contrary to previous reports, adding oblique images does not improve accuracy for this configuration. Moreover, neither extra sets of images nor an expert pilot are required. These topographies allowed the detection of 93.5% more discontinuities than the Above Mean Sea Level surveys, the common approach used in mining areas. Our findings improve the present SfM-UAV survey workflows in long highwalls. The versatile topographies are useful for the management and stabilization of highwalls during phases of operation, as well closure-reclamation.

Performance Analysis of a Drone Development Kit-derived Digital Elevation Model

“…Afterward the mean distances between the two data sets and the standard deviation of this distance are calculated. The mean distance represents accuracy, while the standard deviation represents precision (Zapico et al, 2021). In the concept of comparing DEMs, the spatial distribution of vertical discrepancies is tried to be revealed.…”

“…In the last decade, different remote sensing systems such as visible light and multispectral cameras, Light Detection and Ranging (LiDAR) have been used as payloads of unmanned aerial vehicles (UAVs) or drones (Akturk and Altunel, 2019;Carpenter et al, 2023;Zhang and Zhu, 2023). Nevertheless, visible light cameras continue to maintain their prevalence and dominance among the available options for DEM production, primarily attributed to their cost-effectiveness (Bi et al, 2021;Giordan et al, 2020;Kovanič et al, 2023).…”