DEM-Based Radar Incidence Angle Tracking for Distortion Analysis without Orbital Data

Synthetic Aperture Radar (SAR) is a crucial technique in Earth observation, providing vast amounts of data for monitoring the Earth's surface. However, SAR's side-looking imaging characteristics often result in significant geometric distortions in complex terrains such as mountainous gorges. Current methods struggle to accurately compute both active and passive geometric distortions when orbital state vector information is not available. This study aims to address this challenge by concentrating on the Southeastern Tibetan Plateau (SETP) and introducing a DEM-Based Radar Incidence Angle Tracking Method (Angle-Tracking) based on ray tracing principles. The fundamental aspects of this method include constructing the Discrete Range Direction Vector (DRDV) to establish calculation directions, refining grid distribution via cubic-patch cells, and identifying Potential Topographic Occluder Points (PTOPs) to minimize redundancy in iterative computations. Through the utilization of this approach, we have acquired and disclosed the distribution of geometric distortion in ascending and descending Sentinel-1 data over the SETP region. Cross-validation with results computed from precise orbital data showcases the efficacy of the Angle-Tracking method in identifying geometric distortions in the absence of satellite state vector information. Furthermore, the Angle-Tracking method demonstrates effectiveness when implemented on cloud computing platforms like Google Earth Engine, thereby enhancing the feasibility of SAR-based research in mountainous areas.