Evaluation of the Detectability of Road-Slope Displacements Considering SAR Satellite Direction and Incidence-Angle Effects in South Korea

  Approximately 70% of South Korea’s land is mountainous, and as expressways and national highways have expanded across this terrain, extensive roadside slopes have been formed. Although various reinforcement and stabilization measures were applied during road construction, failures, such as collapses and settlements, continue to occur due to heavy rainfall, typhoons, and other extreme weather events.

  In recent years, South Korea has initiated research efforts to utilize imagery acquired from Synthetic Aperture Radar (SAR) satellites to detect long-term ground displacements along roadside slopes and support preparedness for potential geohazards.

  This study assessed the detectability of ground displacements on road slopes by considering the motion direction and incidence angle characteristics of SAR satellites over the Korean Peninsula.
  SAR satellites can acquire high-resolution images regardless of daylight or weather conditions. Furthermore, interferometric techniques (InSAR) enable the generation of digital elevation model (DEM) with sub-meter accuracy and ground displacement estimations with millimeter-level precision.

  However, as radar satellites observe the Earth at oblique angles relative to their flight direction and employ side-looking geometry perpendicular to the line of sight, geometric distortion may occur in areas with highly irregular terrain. In such conditions, shadowing effects—including layover and radar shadow can arise where radar signals are unable to reach. Steep road slopes are particularly susceptible to these limitations, and accurate observation may be impossible depending on the satellite’s motion direction and incidence angle. Therefore, before applying SAR data to slope-monitoring studies, it is essential to assess the feasibility of observations for the target slopes.

  In this study, the motion and observation characteristics of the Sentinel-1B satellite which continuously acquires imagery across the Korean Peninsula at approximately 12 day intervals were analyzed to evaluate the feasibility of observing road slopes nationwide.

  To evaluate the SAR observation feasibility for road slopes in South Korea, the evaluation was conducted in three stages: 1. Road-slope information, road networks, and other required datasets were compiled and converted into geospatial (Geographic Information System) data formats. 2. SAR imagery covering the Korean Peninsula was collected, and satellite motion direction and incidence angles were derived from image header files and metadata, then converted into raster datasets. 3. The relative spatial relationship between the road-slope data and satellite-observation data was analyzed, and based on these results, the observation feasibility of each road slope was evaluated considering the effects of the SAR satellite’s motion direction and incidence angle.

  As a result, the study evaluated the SAR observation feasibility for approximately 27,000 road slopes across South Korea. Considering the orbit and incidence-angle characteristics of the Sentinel-1B satellite, it was found that about 66% of all slopes were located within the satellite’s effective imaging range.

Acknowledgement

This research is based upon work supported by Korea Institute of Civil Engineering & Building Technology(KICT), Project No.20250285-001