Spaceborne Sar Imaging Center Calibration Using Space-Ground Cooperative Approach

The spaceborne Synthetic Aperture Radar （SAR） spotlight mode is characterized by high resolution and narrow swath width, which requires strict matching between the imaging center and the ground planning results to ensure the successful execution of the mission. When imaging large-scale areas in spotlight mode, multi-orbit and multi-pass imaging is needed to meet coverage requirements while maintaining a strict image overlap rate, providing support for subsequent mosaicking or stereo mapping. Even a slight deviation of the imaging center will lead to insufficient overlap rate or gaps in images, forcing the satellite to perform a large number of supplementary imaging operations and significantly reducing the operational efficiency and economy of the SAR satellite. The deviation of the imaging center is comprehensively affected by orbit extrapolation errors, star sensor installation errors, and payload installation errors. Traditional geometric calibration methods rely on capturing ground control points, mainly solving geometric positioning problems, but their correction effect on imaging center deviation is limited. To meet the high-precision positioning requirements of large-scale spotlight imaging, a satellite-ground collaborative calibration method is proposed: the on-board system adopts an autonomous orbit prediction algorithm, fuses GNSS real-time positioning data with the J2 perturbation model to suppress orbit propagation errors, efficiently determines the imaging center time through a binary search algorithm, and updates key parameters such as slant range and incident angle in real time; The ground system, based on Level-2 products, uses recursive least squares fitting technology to invert the star sensor calibration matrix, compensating for the systematic installation deviation between the SAR antenna and the star sensor. Experimental verification on the Shenqi C-band lightweight commercial SAR satellite shows that in 100 consecutive spotlight imaging missions, this method reduces the average offset of the imaging center from 800 meters to within 100 meters, effectively reducing the need for supplementary imaging and improving data acquisition efficiency.