Abstract
The sub-satellite track of geosynchronous synthetic aperture radar (GEO SAR) presents the figure 8 or O, which causes the great changes of platform motion direction and the different projection of anisotropic irregularities along the line-of-sight (LOS) direction. Due to the almost equal angle velocity to that of Earth, the GEO SAR has smaller ionospheric penetration point (IPP) scanning velocity which is much smaller to the counterpart of the low earth orbit SAR (LEO SAR) while is comparable to the drifting velocity of irregularities, which will affect the effective azimuthal velocity. These facts lead to the consequence that the satellite signals from the GEO SAR would become more vulnerable when they are transmitted in the environment where the ionospheric scintillation occurs. However, few works are focused on these mentioned issues towards the GEO SAR system. In this paper, the impacts of ionospheric scintillation on GEO SAR imaging will be analyzed considering the anisotropy and drifting velocity of irregularities. The anisotropy and drifting velocity effects can both originate from the effect on power spectral density (PSD) of phase screen which is used to model the ionospheric scintillation effects. Based on the data from international geomagnetic reference field (IGRF) and satellite tool kit (STK), the GEO SAR imaging simulations for different GEO SAR orbital configurations and positions are carried out. The simulation results demonstrate that the anisotropy and the drifting velocity of irregularities will cause the changes of stripe direction and affect the quality of GEO SAR images.
Highlights
The ionospheric irregularities in the ionosphere will introduce the amplitude and phase fluctuations to the signals from the geosynchronous synthetic aperture radar (GEO SAR), i.e. ionospheric scintillation [1], which will introduce the light and dark stripes and defocusing on SAR images
This paper studies the impacts of anisotropic and drifting irregularities on GEO SAR based on the modified power spectrum density (PSD)
When the signal propagates from the ground back to GEO SAR, the signal will be affected by ionospheric scintillation at different spatial positions, so the different amplitude and phase fluctuations are introduced in the aperture: s2r (t, u) = σp · s0 (t, u) · DITF2 (u; θA, ζA) (15)
Summary
The ionospheric irregularities in the ionosphere will introduce the amplitude and phase fluctuations to the signals from the geosynchronous synthetic aperture radar (GEO SAR), i.e. ionospheric scintillation [1], which will introduce the light and dark stripes and defocusing on SAR images. X. Dong et al.: Modeling and Analyzing Impacts of Drifting Anisotropic Ionospheric Irregularities on Inclined GEO SAR irregularities and causes SAR images defocusing. The angular velocity of GEO SAR is equivalent to that of the Earth rotation, leading to the IPP scanning velocity of GEO SAR is comparable to the drift velocity of irregularities in some orbital positions. Both of two velocities will affect the effective azimuthal velocity. The high latitude anisotropic irregularity effects were analyzed based on the observations of ALOS PALSAR [13], [14] These studies didn’t consider the influences of anisotropy and drifting velocity of irregularities on GEO SAR imaging for area targets.
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