Satellite based multi-scale remote sensing system for infrastructure stability monitoring around an urban metro

Ground settlement around urban metro systems can result from coupled interactions among wide-area surface displacement, local surface geometry, shallow subsurface conditions, and underground structural deformation. However, a single monitoring technique is insufficient to screen settlement-prone sections along long metro corridors and to interpret the associated surface and underground conditions at the selected site. This study proposes a multi-scale remote sensing system (MSRS) integrating InSAR, laser scanning, GPR, and BOTDR-based distributed fiber optic sensing for infrastructure stability monitoring around an urban metro ventilation facility. First, SBAS-InSAR analysis was performed along the approximately 16 km Bundang Line corridor between Suseo Station and Cheongnyangni Station in Seoul, Korea, to detect long-term LOS displacement tendencies. The corridor is a densely built urban area in which the alignment runs beneath paved arterial roads, and the target ventilation facility lies less than 10 m below ground surface. Based on the InSAR screening result, a ventilation facility near Gangnam-gu Office Station, where a relatively distinct settlement tendency was identified, was selected as the local target site. Ground-surface laser scanning was then used to resolve the present geometry of the localized surface depression around the ventilation facility, while GPR was applied to investigate pavement-layer thickness variations and localized reflection anomalies beneath the settlement area. Inside the ventilation chamber, underground laser scanning and BOTDR-based DFOS were used to evaluate the structural deformation. The temperature-corrected BOTDR result showed strain values ranging from approximately − 250 to + 350 με, with the maximum near 170–178 m and a second localized increase between 117 and 124 m, where a ceiling crack was mapped during the field inspection. These results indicate that the proposed MSRS can effectively screen settlement-prone sections along urban metro corridors and support staged interpretation of surface deformation, shallow subsurface conditions, and underground structural responses.