Tracking slow-moving landslides with PlanetScope data: new perspectives on the satellite's perspective

PlanetScope data with daily temporal and 3 m spatial resolution hold an unprecedented potential to quantify and monitor surface displacements from space. Slow-moving landslides, however, are complex and dynamic targets that alter their topography over time. This leads to orthorectification errors, resulting in inaccurate displacement estimates when images acquired from varying satellite perspectives are correlated. These errors become particularly concerning when the magnitude of orthorectification error exceeds the signal from surface displacement, which is the case for many slow-moving landslides with annual velocities of 1-40 m yr-1. This study provides a comprehensive assessment of orthorectification errors in PlanetScope imagery and presents effective mitigation strategies for both unrectified Level 1B (L1B) and orthorectified Level 3B (L3B) data. By implementing these strategies, we achieve sub-pixel accuracy, enabling the estimation of realistic and temporally coherent displacement over landslide surfaces. The improved signal-to-noise ratio results in higher-quality displacement maps, allowing a more detailed analysis of landslide dynamics and their driving factors.