Study of Ionospheric Effects on Azimuth Imaging for Medium-earth-orbit Sar

The Medium-Earth-Orbit SAR (MEOSAR) is one of the most potential next-generation spaceborne SARs for its excellent performances. However, the MEOSAR may not be able to produce data useful for science applications due to ionospheric effects. So it is very necessary to study ionospheric effects for the development of MEOSAR. In this paper, we present ionospheric effects on azimuth imaging for MEOSAR. First, we established an analysis model for ionospheric effects on azimuth imaging of MEOSAR based on the system characteristics of MEOSAR and the temporal-variability of ionosphere. Then, based on the analysis model, we analyzed the effects caused by the quadratic and cubic phase errors induced by temporal-variability of ionosphere on azimuth imaging. According to the results of our analysis, we conclude that both the quadratic phase error and the cubic phase error neglected for Low-Earth-Orbit SAR (LEOSAR) will deteriorate the azimuth imaging for MEOSAR. Furthermore, ionospheric effects will become more and more serious with the increase of SAR altitude and the improvement of azimuth resolution designed.