Multi-Sensor Remote Sensing Framework for Urban Ground and Building Deformation Monitoring in the Slănic Salt-Karst Area (Romania)

Urban areas affected by salt-karst processes are highly vulnerable to ground instability, infrastructure damage, and rapid geomorphological changes. The Slănic area (Romania), affected by active dissolution, suffosion, and anthropogenic activity, represents a complex urban environment where recent collapse events, including the major 2024 failure in the city center, have emphasized the necessity of integrated remote sensing approaches for deformation monitoring and hazard assessment.

This study presents a multi-temporal and multi-scale remote sensing framework for monitoring both terrain and building deformation in the urban area of Slănic. The study integrates UAV LiDAR, airborne LiDAR, UAV photogrammetry, Sentinel-1 Multi-Temporal InSAR (MT-InSAR/PSI), GNSS observations, terrestrial laser scanning (TLS), geometric leveling, and total station measurements using prisms installed on buildings. UAV campaigns generated high-density point clouds, centimeter-resolution orthophotos, and Digital Terrain Models, while airborne LiDAR ensured regional-scale geomorphological continuity across the salt-karst basin.

Sentinel-1 ascending and descending datasets processed between 2018 and 2024 revealed persistent subsidence patterns with deformation rates reaching ~2 cm/year, particularly near active suffosion zones and densely urbanized sectors. TLS surveys and repeated prism measurements enabled detailed three-dimensional assessment of building inclinations, localized settlements, fractures, and structural displacements at centimeter- to millimeter-scale precision. GNSS and leveling observations independently validated deformation signals derived from remote sensing datasets.

The integration of satellite, airborne, and close-range sensing techniques demonstrates the significant potential of multi-sensor remote sensing for urban deformation monitoring, infrastructure stability assessment, and early-warning support in unstable salt-karst environments.

Acknowledgements.

This work was carried out within the project No. 28Sol(T28) ⁄2025, funded by the Ministry of Education and Research, through UEFISCDI (Romanian Executive Agency for Higher Education, Research, Development and Innovation Funding).