Abstract
The geosynchronous synthetic aperture radar (GEO SAR) is susceptible to orbit perturbations, leading to orbit drifts and variations. The influences behave very differently from those in low Earth orbit (LEO) SAR. In this paper, the impacts of perturbations on GEO SAR orbital elements are modelled based on the perturbed dynamic equations, and then, the focusing is analyzed theoretically and numerically by using the Systems Tool Kit (STK) software. The accurate GEO SAR slant range histories can be calculated according to the perturbed orbit positions in STK. The perturbed slant range errors are mainly the first and second derivatives, leading to image drifts and defocusing. Simulations of the point target imaging are performed to validate the aforementioned analysis. In the GEO SAR with an inclination of 53° and an argument of perigee of 90°, the Doppler parameters and the integration time are different and dependent on the geometry configurations. Thus, the influences are varying at different orbit positions: at the equator, the first-order phase errors should be mainly considered; at the perigee and apogee, the second-order phase errors should be mainly considered; at other positions, first-order and second-order exist simultaneously.
Highlights
Geosynchronous synthetic aperture radar (GEO SAR) [1] runs on an orbit height of around36,000 km, has a revisit time of less than 24 h and a coverage of more than 1000 km by 1000 km
In [18], the perturbation effects are analyzed for the GEO SAR in a circular geosynchronous orbit, and the approximate perturbed equations are adopted in analyzing the errors of the Doppler parameters and the focusing performance
This paper studies the perturbation influences on the orbital elements, the slant range histories and the focusing performance of GEO SAR based on the accurate numerical simulation using Systems Tool Kit (STK)
Summary
Geosynchronous synthetic aperture radar (GEO SAR) [1] runs on an orbit height of around. The perturbed orbit variations within one day or the GEO SAR aperture time (several hundreds or even thousands of seconds) can lead to the changing of the slant range histories and result in the degradation and even the failure of focusing [17,18]. In [18], the perturbation effects are analyzed for the GEO SAR in a circular geosynchronous orbit, and the approximate perturbed equations are adopted in analyzing the errors of the Doppler parameters and the focusing performance. This paper studies the perturbation influences on the orbital elements, the slant range histories and the focusing performance of GEO SAR based on the accurate numerical simulation using STK. As the analytical solution for perturbation dynamic equations and their composited influences on the slant range are difficult to obtain, a numerical approach based on STK is adopted to construct the SAR signals. The focusing and evaluations are performed to validate the analyses based on the STK simulations
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