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Abstract-This paper presents a new approach to calculate the 1-4th order Doppler parameters for Geosynchronous Synthetic Aperture Radar (Geo-SAR). To get accurate calculation results, the Earth is modeled as an ellipsoid and the relative motion between the sensor in an elliptical orbit and the rotating Earth is analyzed. The J 2 , J 3 and J 4 orbital perturbation items and attitude steering are analyzed. Ignoring the perturbation force would produce errors of the Doppler parameters for spaceborne SAR because it can influence the six orbital elements. Since the Doppler parameters are related to the antenna beam pointing directions and influenced by attitude of SAR platform, the calculation results before and after attitude steering are shown. Furthermore, the Doppler parameter properties during the whole orbital periods of Geo-SAR are compared with those of Low-Earth-Orbital SAR (Leo-SAR). Finally, the effects on Doppler parameters stemmed from the radar beam pointing accuracy are analyzed.

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Ship targets are high-value military and civilian targets with broad application prospects. However, the precise focusing of ships is still a difficult issue because of their complicated six-degree-of-freedom motions on the sea surface. This paper focused on investigating the effect of ship six-degree-of-freedom oscillation on Synthetic Aperture Radar imaging. Firstly, based on the six-degree-of-freedom motions, the accurate range models for ship linear oscillation and angular oscillation were built, and the superiority was verified by comparing them with the models described in published literature. Secondly, we used the Taylor formula and Bessel function to expand the phase error introduced by ship oscillation, then their effects on imaging were further analyzed. Finally, based on the measured ship attitude data, we generated the semi-physical echoes of the oscillatory ship to validate the analysis throughout this article. Based on the proposed range model, we also made some tentative on the phase compensation method by fitting ship attitude angles with multiple sinusoidal functions.