Terrestrial laser scanner versus ground-based structure from motionphotogrammetry for sinkhole characterization and monitoring in an urban area. A comparative assessment in the evaporite Karst of Zaragoza city, Ne Spain

Abstract

Delimiting, characterizing, and monitoring active sinkholes in urban areas are fundamental steps for effectively managing the associated risks. These high-exposure scenarios require accurate data on hazard parameters (e.g., spatially-distributed subsidence rates), but the current investigation and monitoring techniques for sinkholes remain relatively undeveloped in comparison to other geological hazards, such as landslides. In this regard, we present the first comparative analysis of the performance of Terrestrial Laser Scanner (TLS) and ground-based Structure from Motion (SfM) photogrammetry for delimiting the actively deforming areas and characterizing the spatial patterns of ground displacement through the comparison of two pairs of high-resolution 3D point clouds. To assess their performance this work utilizes vertical displacement data measured by high-precision leveling. The main finding is that, despite TLS provides displacement data with less noise and internal distortion, the less expensive and easier-to-implement SfM photogrammetry using ground-based conventional cameras yields a comparable performance when accurate geodetic data is available. However, according to high-precision leveling data, both techniques may underestimate the extent and rate of the deformation, indicating that there is still the need to complement these high-resolution techniques with the use of high-precision methods such as leveling or additional geodetic benchmarks.