Research on Automatic Control Point Extraction and Correction Method for High-Resolution Synthetic Aperture Radar Imagery Assisted by Multi-source Data

Ground control points (GCPs) are essential for improving the positioning accuracy of remote sensing imagery. Their spatial distribution and geometric quality directly affect the reliability of orthorectification. GCPs serve as a critical foundation for ensuring the accuracy of multi-source image fusion, change detection, and quantitative inversion. However, traditional corner reflector deployment presents high costs and implementation difficulties, struggling to meet global application demands. Additionally, existing heterogeneous control points (such as optical imagery and laser altimetry data) exhibit significant modal differences relative to synthetic aperture radar (SAR) imagery, which affects their ability to balance accuracy and robustness. To address these challenges, this study proposes an automatic control point extraction method for high-resolution SAR imagery based on multi-source data. Furthermore, a high-precision orthorectification framework is established using control chips. The method leverages the characteristics of widely distributed pole-like artificial features in urban environments: these features exhibit a body–shadow collaborative structure in optical imagery and a cross-shaped strong scattering response in SAR imagery. First, open-source airport runway data are used to correct Google optical imagery, establishing a planar reference framework. Next, initial positioning optimization for stereo SAR images from ascending and descending orbits is achieved by jointly adjusting optical-SAR and stereo SAR image matching points. Finally, road and parking lot vector data are utilized to extract regions of interest, where strong scattering points are identified using a signal-to-clutter ratio detection algorithm. Three-dimensional spatial coordinates of control points are obtained via point target analysis and stereo positioning techniques. After correcting residual planar errors in stereo SAR images using control point coordinates, control chip data for ascending and descending orbit SAR images are generated. Validation experiments using GaoFen-3 SAR images from multiple regions show that the 3D positioning accuracy of control points extracted from spotlight mode stereo SAR imagery reaches the submeter level. Orthorectification of test images using extracted control points and control chips significantly improves positioning accuracy, as verified by corner reflectors and airborne LiDAR point cloud-based ground truth. Positioning errors are 1.78 pixels (spotlight mode), 1.09 pixels (ultrafine stripmap mode), and 0.82 pixels (fine stripmap mode), corresponding to improvements of 47.2%, 49.3%, and 37.4%, respectively, compared to traditional optical reference image matching correction methods. This study introduces crowdsourced information to assist SAR control point extraction and ascending/descending orbit SAR control chip construction, overcoming the accuracy limitations of optical reference image matching correction. The proposed method provides a scalable approach for high-precision positioning and joint processing of high-resolution SAR imagery.