Application of UAV photogrammetry for the multi-temporal estimation of surface extent and volumetric excavation in the Sa Pigada Bianca open-pit mine, Sardinia, Italy

Abstract

In open-pit mines, monitoring of topographic and volumetric changes through time is found to be of great importance to support excavation stages and to plan rehabilitation strategies. In this work, we describe a geomatic approach to assess changes in surface mine extent and to quantify excavated volume in the Sa Pigada open-pit mine, Sardinia, Italy. We performed two drone-based photogrammetric surveys in 2013 and 2015, and by means of the Structure from Motion (SfM) technique, we obtained related 3D dense point clouds and digital orthophotos. Images were georeferenced thanks to a series of ground control points surveyed with geodetic GPS. Distances between the two clouds were estimated with the recent Multiscale Model to Model Cloud Comparison (M3C2) plug-in included in the CloudCompare open-source software. Starting from cloud-to-cloud distances, we calculated the excavated volume of mineral resources between the two surveys. Results of the M3C2 comparison supported the analysis of the two orthophotos, through which accurate limits of the 2013 and 2015 active mine areas, rehabilitated area and temporary dumps were identified and drawn in a digital map. Results obtained in this study suggest that the applied geomatic techniques are suitable for performing accurate change detection analysis in open-pit environments and represent a valid support for scientists and technicians allowing to monitor with high spatial and temporal resolutions. This approach can be also considered a valid tool to reduce environmental impact from mining

Geovisualisation of Relief in a Virtual Reality System on the Basis of Low-Level Aerial Imagery

“…The conducted study was inspired by the paper of Esposito et al (2017), who outlined the possibilities of using UAV technology for monitoring open pit mines, especially recording the changes taking place and performing cubature calculations on the basis of the point cloud. In addition, this paper aimed to further the research done by Slater et al (2010) concerning the possibility of using VR for a more immersive exploration of 3D geovisualisation in the VR FPV mode.…”

“…The possibility of using the UAV technology to monitor open pit mines, especially with the purpose of tracking the occurring changes and making cubature calculations on the basis of the point cloud, has been described, among others, by Esposito et al (2017) based on the example of Sa Pigada Bianda in Sardinia. Due to the technological development of the miniaturisation process and the decreasing production costs of the components used in UAV construction, the vehicles are becoming more and more popular as surveying platforms in geophysical research.…”

Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall

“…Figure 6 shows the trend of increasing volumetric estimations as a function of grid size. Esposito et al (2017) performed a sensitivity analysis of the cell size on the volumetric estimations of an excavated mine and found that the estimated volume increased with cell size, and then used 50 cm as optimal cell resolution. The effect of grid size on volumetric assessments was expected.…”

“…where σ 1 (d) and σ 2 (d) are calculated as the standard deviations of elevations of the subset of points (I, J) in the cylinder, and n 1 and n 2 are the number of subset of points in the cylinder (see 'Elevation change calculation', above) (Lague et al, 2013;Esposito et al, 2017).…”

“…The effect of grid size on volumetric assessments was expected. Vericat et al (2014) previously highlighted the importance of Esposito et al (2017) performed a sensitivity analysis of the cell size on the volumetric estimations of an excavated mine and found that the estimated volume increased with cell size, and then used 50 cm as optimal cell resolution. It is not possible to definitively determine the optimum cell size for our experiments; nevertheless, volumetric estimation based on the 10 mm grid was used for further analyses because the cell size effect on the estimated volumes became much less sensitive at that cell size.…”