Application of UAV Photogrammetry to Slope-Displacement Measurement

To reduce accidents caused by slope failures, disaster assessments and displacement measurements of steep slopes are conducted. Measurement values can vary greatly, depending on the technician’s proficiency. Moreover, land creep and minute displacements are difficult to detect. In this study, we attempted to solve this problem using unmanned aerial vehicles (UAVs) and aerial triangulation. After a review of previous studies, a measurement precision of 10 cm for daily monitoring and sub-centimeters for precise monitoring were set. Twelve checkpoints were used, and the comparison results between the measured values using the total station and the aerial triangulation using the UAV were as follows. A virtual reference station (VRS) and three ground control points (GCPs) yielded 11.58 mm for the 3D (root-mean-square error) RMSE, and post-processed kinematic (PPK) and three GCPs generated 9.71 mm. By differentiating the results of multiple observations, the PPK processing results could achieve sub-centimeter accuracy. We verified that direct georeferencing using a VRS is sufficient for daily monitoring, and precise measurements require at least three GCPs. Geotechnicians can use VRS observations for economical slope monitoring in normal times, and accurate observations with GCPs when precise measurements are required.