Ionosphere-induced first and higher order errors for space based SAR

Satellite borne SARs need to be operated at low frequencies (HF, VHF) to obtain good penetration through vegetation. At these lower frequencies the effect of the ionosphere is appreciable and the phase variation (in radians) with frequency is higher order than f ^-1. The magnitude of these higher order phase terms in f ^-2 and f ^-3 (in radians) are determined for all frequencies between 50 and 100 MHz for both magneto-ionic modes and for a range of elevations and azimuths (with respect to the magnetic meridian), time of day, month of the year and R12. Calculations are performed for a realistic 3D electron density distribution including both vertical and horizontal gradients of electron density (given by the NeQuick model) to assess accurately these higher order terms for a SAR at 600 km altitude for different ionospheric conditions.