Combined spaceborne and ground-based InSAR for deformation monitoring of portal slopes of long-span highway tunnel

Abstract

Interferometric Synthetic Aperture Radar (InSAR) technology has been widely adopted for deformation monitoring of transportation infrastructure. However, monitoring alpine high-altitude mountain tunnels remains challenging due to complex geology and frequent landslides. Conventional single InSAR techniques suffer from monitoring blind zones caused by terrain layover and shadow, and only provide one-dimensional deformation data, failing to simultaneously implement large-scale hazard screening and high-precision real-time tunnel portal monitoring. This paper proposes a multi-level deformation monitoring framework integrating space-borne InSAR, ground-based InSAR and LiDAR. First, ascending and descending orbit SBAS-InSAR integrated with SAR geometric visibility analysis is adopted to remove layover and shadow distortion areas. A dual-orbit 2D deformation inversion model is constructed to retrieve vertical and east-west deformation fields along the tunnel alignment, enabling macroscopic full-scale screening of hidden geological hazards. Subsequently, ground-based InSAR is fused with 3D LiDAR, and a multi-criteria hierarchical PS point screening framework is established to improve the precision of monitoring targets via multi-constraint optimization. Coordinate registration and 3D projection algorithms are applied to realize accurate 3D visualization of one-dimensional slope deformation data. Finally, experimental validation is conducted based on an extra-long alpine high-altitude tunnel in Xinjiang. The proposed method accurately identifies high-risk tunnel portal areas and captures real-time millimeter-scale local micro-deformations at tunnel portals. Validations demonstrate that the integrated monitoring method adapts to harsh mountainous monitoring environments and integrates advantages of large-area general survey and high-precision local detailed measurement, providing solid technical support for slope disaster prevention during construction and operation of mountain tunnels.