The Effects of Orbital Perturbation on Geosynchronous Synthetic Aperture Radar Imaging

Compared with current low-Earth-orbit synthetic aperture radar (SAR), geosynchronous SAR (GEO SAR) is featured with its ultrahigh orbit and ultralong integration time. In this letter, we answer the question whether the orbital perturbation items have effects on GEO SAR imaging during the long integration time and, if so, how they produce errors. To achieve these goals, we first develop a perturbing orbital elements errors model based on perturbation analysis. Then, we propose an accurate analytical expression of first to fourth Doppler parameters for GEO SAR and analyze the effects of perturbing orbital elements errors on the Doppler parameters. Furthermore, the relationship between the perturbing Doppler errors and the phase coherence of GEO SAR signal is deduced. Experiment and simulation results demonstrate the image defocusing caused by orbital perturbation. The conclusions are that the orbital perturbation does affect GEO SAR imaging by producing nonnegligible phase errors and that the required accuracy of the orbit determination should be at centimeter level in the radial direction.