Analysis of Temporal-Spatial Variant Atmospheric Effects on GEO SAR

Abstract

Due to the ultra-long integration time and large coverage characteristics of geosynchronous synthetic aperture radar (GEO SAR), the atmospheric frozen model in the traditional low Earth orbit SAR (LEO SAR) imaging fails in GEO SAR. The temporal-spatial variation of troposphere and ionosphere should be taken into account for the GEO SAR imaging. Based on the accurate GEO SAR signal model, the two-dimensional spectrum of GEO SAR signal in the context of temporal-spatial variant troposphere and background ionosphere are derived, and then the two-dimensional image shift and defocusing are investigated. The boundary conditions of relevant effects are analyzed and summarized which are related to the status of troposphere and background ionosphere, the GEO SAR imaging geometry and the integration time dependent on the resolution requirement. GEO SAR is also sensitive to ionospheric scintillation which causes the amplitude and phase fluctuations of signals. The corresponding degradation will have a different pattern from LEO SAR. The azimuth point spread function considering the scintillation sampling model is constructed. Then, based on the measurable statistical parameters of ionospheric scintillation, performance is quantitatively analyzed. The analysis suggests that in GEO SAR imaging the azimuth integrated side lobe ratio deteriorates severely, while the degradations of the azimuth resolution and azimuth peak-to-sidelobe ratio are negligible when scintillation occurs.