The Precise Analytical Calculation of Fourth-Order Doppler Parameters for Geosynchronous SAR

Compared with current Low-Earth-Orbit spaceborne Synthetic Aperture Radar (LEO SAR), Geosynchronous SAR (GEO SAR) is featured in its ultra-high orbit and ultra-long integration time. Due to the non-linear property of the ultra-long synthetic aperture, the traditional Doppler parameter calculation methods based on the linear motion model are invalid for GEO SAR. A precise analytical algorithm to calculate the fourth-order Doppler parameters for GEO SAR is proposed, analyzed and verified in this paper. We first proposed the analytical expression of fourth-order Doppler parameters for GEO SAR, and the results can be used in arbitrary ellipse orbit cases. Then, a precise fourth-order Doppler parameter calculation algorithm is developed based on the deduced formulae. Finally, the accuracy of the calculation algorithm is verified by processing real data of a drifted geostationary satellite experiment.