Robust Retrieval of Slope-Parallel Landslide Displacements From Single-Track InSAR Observations: A Line of Sight (LOS) Sensitivity Correction Framework

Landslides in mountainous regions exhibit widespread distribution and high recurrence, posing critical threats to human safety and socioeconomic assets. Interferometric Synthetic Aperture Radar (InSAR) has proven instrumental in landslide identification, continuous monitoring, and early-warning systems. Nevertheless, the inherent side-looking geometry of SAR systems restricts displacement measurements to the line-of-sight (LOS) direction, which may misrepresent true slope-parallel displacement and cause substantial inconsistencies between ascending/descending track-derived results and actual ground movement. To address this limitation, this study introduces the concept of LOS sensitivity (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LS</i>) and systematically quantifies geometric distortion effects on LOS measurements across diverse slope gradients and aspects. We propose an innovative LOS Sensitivity Correction (LSC) framework that integrates geometric distortion correction through joint optimization of topographic parameters and SAR interferometric processing configurations, enabling precise retrieval of slope-parallel displacement from single-track InSAR observations. Validation experiments utilizing Sentinel-1 ascending/descending datasets over the Ermulin and Huanglianping landslides demonstrate that while conventional D-InSAR results exhibit significant inter-track discrepancies (exceeding 40 mm in magnitude), LSC-processed displacements achieve remarkable consistency in deformation patterns (correlation coefficient >0.92) and spatial distribution. We further analyzed the influence of topographic parameters and interferometric processing configurations on LSC, revealing their effects on the correction results. The proposed methodology comprehensively resolves LOS sensitivity challenges for slopes with arbitrary geometries, advancing the fundamental understanding of terrain-dependent SAR detection limitations while transcending the simplistic formulaic application of conventional correction frameworks. This work establishes a paradigm for robust interpretation of slope-parallel kinematics from single-track InSAR products, with direct implications for landslide hazard assessment and mitigation strategies in complex terrains.