Sidelobe prediction in transionospheric SAR imaging radar from the ionospheric turbulence strength CkL

Space based synthetic aperture radar (SAR) is an important imaging technique which necessarily involves imaging through the ionosphere. This represents a significant limiting factor, especially at low frequencies (VHF, UHF and L-band). The point spread function sidelobes, peak sidelobe ratio and integrated sidelobe ratio (ISLR) are an important measure of SAR image quality, and ultimately determine whether a focussed image can be generated. This paper shows how it is possible to predict the SAR image quality from the integrated ionospheric turbulence strength parameter, C_kL, and the S₄ index. Since the statistics of C_kL are known (and have been measured for many years) this will allow the probability of achieving a particular image quality to be determined.