Lessons Learned from the Application of UAV-Enabled Structure-From-Motion Photogrammetry in Geotechnical Engineering

The application of the Structure-from-Motion (SfM) methodology, as enabled by the growth of Unmanned Aerial Vehicle (UAV) technology, is expected to have significant impact in geotechnical engineering research and practice. SfM outputs are presented using selected geotechnical projects as examples, and include orthophotos, 3D point clouds, and three dimensional digital surface or terrain models. Repeated surveys allow for monitoring of deformation patterns at a cm-level resolution. The lessons learned from the application of the methodology at twenty-six sites that cover the breadth of geotechnical engineering practice, located in four countries (USA, Greece, Nepal, and New Zealand) and variable geologic environments are presented. It is shown that the methodology leads to an unprecedented level of mapping that covers large areas at high resolution. In addition to the high resolution models, SfM models are shown to be comparable in accuracy to other surveying techniques and mapping technologies such as light detection and ranging (LiDAR). The advantages and disadvantages of the methodology are also presented with the intent to facilitate the greater incorporation of this methodology in geotechnical engineering. The use of UAVs makes the methodology especially appealing for immediate post-disaster response as it enables the collection of optical data in areas that are inaccessible or unsafe.