Impact of Earth’s Oblateness Perturbations on Geosynchronous SAR Data Focusing

In this study, we focus on the ultra-long integration of orbital perturbations of geosynchronous Synthetic Aperture Radar (SAR) for imaging. By deriving mathematical expressions for the Doppler rate and quadratic phase from orbital elements perturbated by oblateness or the J2 term of the non-spherical gravitational force of the Earth, we analyze the impact on SAR data focusing. Based on our results, we conclude that the quadratic phase will exceed 45°, which is the defocusing threshold for imaging, after accumulation during a long integration time at the minute level. Because the potential for defocusing exists throughout nearly the entire satellite motion cycle, the SAR processor must carefully manage and compensate for the quadratic phase to avoid image degradations