Scholarly record
DETECTING URBAN GROUND INSTABILITY USING RECURRENT UAV LIDAR SURVEYS: CAPABILITIES AND LIMITATIONS FROM A SALT-KARST MONITORING SITE IN ROMANIA
Abstract
Urban areas developed above salt-karst systems are particularly sensitive to ground deformation processes driven by dissolution, suffosion, and anthropogenic disturbances. Detecting and monitoring these processes in densely built environments requires observation techniques capable of capturing small-scale morphological changes with high spatial resolution and repeatability. This study demonstrates the use of recurrent UAV-based LiDAR surveys to detect and measure ground instability in the town of Slanic Prahova (Romania), an urban area impacted by active salt-karst processes. The monitoring was carried out as part of the GEOMONITOR project and targeted several sectors showing signs of instability, including the area near a monitoring borehole where drilling encountered a subsurface cavity. Three UAV LiDAR surveys conducted between September 2025 and January 2026 enabled the generation of high-density point clouds and detailed digital terrain models suitable for multi-temporal comparison. Change detection analysis revealed localized deformation patterns affecting two main areas of instability. In the sector surrounding the borehole site, mean subsidence values of approximately 7 - 10 cm were observed, with localized displacements of 25 - 30 cm on terrain and structural elements. Dedicated point-cloud processing workflows allowed accurate co-registration of successive datasets and facilitated the integration of LiDAR-derived products with complementary observations such as GNSS monitoring, precise leveling and terrestrial laser scanning. This integration proved essential for validating deformation signals and distinguishing natural subsidence from anthropogenic surface modifications. The results demonstrate the significant potential of recurrent UAV LiDAR surveys for detecting urban ground deformation at high spatial resolution. At the same time, the study highlights methodological limitations related to surface changes, point cloud classification and interpretation challenges in complex urban environments. Overall, UAV LiDAR monitoring provides valuable high-resolution datasets that support integrated hazard assessment and informed decision-making in urban areas affected by salt-karst instability. This work was supported by the GEOMONITOR project (contract no. 28Sol(T28)/2025), funded by the Ministry of Education and Research through UEFISCDI within PNCDI IV.
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