Applicability Analysis of Corner Reflectors for Satellite SAR Data Collection in Waste Landfill Facility Maintenance

Inadequate post-closure management of waste landfill facilities in South Korea has led to various environmental and social challenges. This study explores the feasibility of using freely available high-resolution satellite Synthetic Aperture Radar (SAR) imagery for continuous monitoring of landfill stability. SAR technology offers clear advantages for monitoring remote or inaccessible sites where permanent on-site personnel deployment is impractical and holds particular promise for developing countries requiring long-term ground stability assessment.

Landfill surfaces pose significant observation challenges for SAR due to vegetation cover and surface objects that degrade measurement quality. To overcome these limitations, artificial corner reflectors were installed at the upper sections of a landfill facility to enhance signal strength and measurement precision. Two types of corner reflectors with different geometries—a conventional triangular trihedral reflector and a cubic reflector—were designed, fabricated, and deployed at a waste landfill site in Pohang, South Korea.

Multi-source SAR datasets were analyzed, including 19 Sentinel-1A images acquired between October 2023 and October 2024, and 7 TanDEM-X images captured at 11-day intervals from September 2024 to January 2025 along ascending orbits. Ground displacement was estimated using Interferometric SAR (InSAR) techniques, with time-series InSAR methods applied to assess temporal deformation patterns.

Comparative evaluation of reflector performance demonstrated that the cubic corner reflector achieved significantly higher signal detection rates than the triangular trihedral design. The cubic reflector exhibited superior radar cross-section characteristics, more stable phase coherence, and lower sensitivity to installation misalignment, indicating its suitability for operational landfill monitoring.

To determine optimal monitoring strategies, various combinations of SAR data sources and processing tools were evaluated. High-resolution commercial SAR data (TerraSAR-X) consistently provided more accurate displacement estimates than freely available Sentinel-1 data across all processing approaches. Nevertheless, Sentinel-1's frequent revisit capability offers substantial advantages for continuous, long-term monitoring applications.

The results confirm that satellite SAR monitoring augmented with appropriately designed corner reflectors represents a practical and cost-effective solution for continuous landfill stability assessment. The integration of ascending and descending orbit data, together with strategically deployed cubic corner reflectors, enables robust three-dimensional ground displacement monitoring. This approach demonstrates strong potential for technology transfer to developing countries where conventional monitoring infrastructure is limited (KICT project No. 20250285-001, second year).