Researchers Unveil Multi-Scale Remote Sensing System to Detect Urban Ground Settlement

Engineers at Seoul National University of Science and Technology have introduced a multi-sensor monitoring framework designed to continuously track urban ground settlement across broad metropolitan regions, as first reported by TechXplore. The remote sensing methodology merges satellite radar analysis, localized laser scanning, and subsurface radar surveys to identify surface subsidence and pinpoint the underlying structural defects causing ground instability.

Ground settlement refers to the downward displacement of the earth's surface or underlying soil layers, typically caused by natural or human-induced shifts in subsurface soil and rock formations. As major metropolitan areas expand their subterranean infrastructure through ongoing excavation for transit lines, utility tunnels, and underground facilities, ground surface settlement has become increasingly frequent. Unintended ground movement presents severe hazards to public safety and can compromise the structural integrity of critical municipal infrastructure, particularly subterranean rail networks like subway systems. Because ground subsidence is notoriously difficult to forecast in advance, continuous wide-area monitoring is required to detect early warning signs.

Despite the necessity of widespread monitoring, conventional tracking methodologies rely on single-mode sensing technologies that cannot provide adequate or reliable coverage across expansive urban environments. For example, monitoring systems that rely on Global Positioning System sensors are incapable of measuring deformation inside subterranean structures, as GPS signals cannot penetrate dense soil or rock layers. On the other hand, satellite-based Interferometric Synthetic Aperture Radar can evaluate ground displacement across vast geographical areas over multi-year timeframes, but its readings are frequently complicated by satellite observation geometry and atmospheric propagation delays that make data interpretation difficult.

To resolve the limitations inherent to single-sensor observation systems, a research team led by master's student Tae-Yong Park from the Department of Civil Engineering at Seoul National University of Science and Technology developed a forensic multi-scale remote sensing system, abbreviated as MSRS. The framework systematically combines satellite InSAR, terrestrial laser scanning (L/S), and ground-penetrating radar (GPR) into a single analytical pipeline. "This innovative fusion of technologies enables not only the detection of ground settlement but also the investigation of its underlying causes," Park explained, noting that the multi-technology approach allows construction defects, improper soil compaction, and excavation-related issues to be identified with far greater precision than single-mode monitoring systems permit.

The researchers validated their forensic MSRS framework by conducting an extensive field deployment along an active municipal transit corridor in South Korea. The pilot study focused on a section of the Seoul Metropolitan Subway Bundang Line extending more than 16 kilometers (10 miles) between Suseo Station and Cheongnyangni Station. The proposed system operates across three distinct operational stages: broad regional monitoring, site-specific validation, and detailed near-surface ground assessment.

In the initial monitoring stage, long-term ground movement was assessed across the entire 16-kilometer transit corridor using satellite InSAR time-series analysis, which measures ground displacement by repeatedly comparing radar signals captured over identical locations over time. To ensure measurement accuracy, the team implemented a mathematical filtering technique known as seasonal-trend decomposition using LOESS, effectively isolating and removing cyclical seasonal fluctuations from the long-term settlement trend. This wide-area analysis highlighted a specific ventilation shaft that exhibited a pronounced deformation signal, and detailed follow-up tracking confirmed the presence of ongoing, progressive ground settlement at the structure.

Following the broad satellite screening, the research team conducted localized field laser scanning directly at the flagged ventilation shaft using LiDAR technology. By generating precise digital point-cloud representations of the target facility, the researchers quantified the exact structural geometry of the shaft. Physical inspection of the site revealed several structural cracks alongside visible evidence of prior maintenance repairs on the ceiling. The laser scanning data further demonstrated a distinct settlement trend across the structure, with deformation growing progressively more severe toward the portion of the ceiling situated directly beneath the adjacent roadside surface.

Based on the laser scanning findings, the researchers executed a ground-penetrating radar survey along the roadway directly above the compromised ventilation shaft. Ground-penetrating radar operates as a non-destructive subsurface investigation tool that emits high-frequency electromagnetic pulses to detect underground features and soil composition. The resulting GPR profiles revealed subsurface signals corresponding to void-like underground structures near the shaft, along with diminished continuity across soil layer boundaries, providing clear evidence of non-uniform subsurface conditions below the road.

By synthesizing data from satellite InSAR, field laser scanning, and ground-penetrating radar into a single visualization model, the researchers achieved cross-interpretation across all three sensing modalities. This integrated analysis proved that the detected ground settlement was a genuine physical anomaly rather than an error or artifact from an individual instrument, thereby minimizing the measurement uncertainties associated with single-dataset reliance. "Our research could help shift the paradigm of urban disaster management from reactive response to proactive prevention," Park stated, adding that the long-term deployment of the MSRS system will allow municipal planners to schedule timely maintenance and target high-risk infrastructure zones before severe hazards such as sinkholes, structural failures, or facility damage occur.