Refining InSAR Deformation Retrieval for the South-to-North Water Diversion via Buffer Optimization

Large-scale linear water diversion infrastructures are highly susceptible to ground deformation induced by groundwater extraction, mining activities, and geological instability, posing potential risks to long-term operational safety. However, conventional SBAS-InSAR monitoring of ultra-long linear infrastructures is often constrained by extensive data volumes, computational burden, and uncertainty associated with empirical buffer selection. To address these issues, this study proposes a practical buffer optimization framework for deformation monitoring along the Middle Route Project (MRP) of the South-to-North Water Diversion Project (SNWDP), China. Using Sentinel-1A SAR images acquired from 2023 to 2024, multiple buffer scales were comparatively evaluated by jointly considering deformation inversion accuracy against leveling measurements and computational efficiency. The results indicate that a 5 km buffer achieves the optimal balance between monitoring reliability and processing efficiency. Validation against first-order leveling benchmarks shows high consistency, with an RMSE of 2.54 mm and an MAE of 2.08 mm. Spatial-temporal analysis reveals significant deformation heterogeneity along the MRP. Severe land subsidence was detected in the Tianjin section due to intensive groundwater exploitation, while localized uplift was observed in parts of Hebei Province, likely associated with groundwater recovery. In addition, pronounced subsidence related to mining activities was identified in Yuzhou, Henan Province. The proposed workflow provides a practical reference for deformation monitoring of large-scale linear water diversion infrastructures and demonstrates the potential applicability of buffer optimization strategies for similar long-distance engineering projects.