Analysis of the Impact of Complex Topography on the Accuracy of Deformation Monitoring by Radar Interferometry

Abstract Interferometric Synthetic Aperture Radar (InSAR) technology offers significant advantages for large-scale, high-precision deformation monitoring and has become a vital method for tracking surface deformation in open-pit mines. However, in areas with complex topography, such as deep concave open-pit mines, radar side-looking geometric distortions and phase aliasing induced by multi-level benches, high-steep slopes, and rugged terrain make Differential InSAR (D-InSAR) and Time-Series InSAR techniques (e.g., SBAS-InSAR) highly sensitive to Digital Elevation Model (DEM) accuracy. Existing research has predominantly focused on flat or gently sloping terrain, leaving a gap in the systematic understanding of error propagation mechanisms across multi-source DEMs and their quantitative impact on InSAR deformation inversion accuracy under complex stepped terrain conditions. Taking the Henan Nannihu Molybdenum Mine as a case study, this study systematically analyzes and compares how multi-source DEMs (ALOS 12.5m, SRTM 30m/90m, TanDEM-X 90m) influence the accuracy of D-InSAR and SBAS-InSAR deformation monitoring. The results indicate that: 1) D-InSAR is extremely sensitive to DEM vertical accuracy. The high-resolution (12.5m), high-accuracy (absolute vertical accuracy of 4.9m) ALOS DEM and its deformation monitoring results are significantly superior to those from SRTM and TanDEM-X DEMs. Its deformation interpretation error is only 0.03–25 mm, and for every 1-meter increase in DEM elevation error, millimeter-level deformation error can be amplified. Furthermore, in areas with slopes > 20%, the phase error from the SRTM DEM can be 3–4 times greater than that of the ALOS DEM. 2) SBAS-InSAR exhibits low sensitivity to DEM errors. By leveraging its multi-temporal phase unwrapping and residual phase correction mechanisms, the differences in monitoring results between various DEMs are restricted to only about 3.9 mm. Systematic elevation errors in DEMs cause significant discrepancies in D‑InSAR results, particularly along steep slopes and abrupt terrain transition zones. In contrast, the variations in SBAS-InSAR results across different DEM datasets are relatively minor. This demonstrates that the two InSAR techniques exhibit distinct distinctly different sensitivities to external DEM inaccuracies. Accordingly, the following optimization strategies are proposed: D-InSAR should prioritize using high-precision ALOS DEM whereas SBAS-InSAR can utilize TanDEM-X DEM combined with Ground Control Points (GCPs) to compensate for errors induced by stepped terrain. Ultimately, this research provides a crucial quantitative theoretical basis and practical guidance for selecting optimal DEM data for InSAR deformation monitoring in complex topographic regions.