Recovering unambiguous differential ionospheric phase screens

Abstract

Synthetic aperture radar interferograms are affected by ionospheric disturbances. The split-spectrum method exploits the peculiar propagation of the radar waves through the ionosphere and recovers a phase screen that can be used to correct the interferogram to improve the estimation of the geometrical phase. However the recovered screen is ambiguous and it is not possible to reach an absolute phase, which would enable absolute geolocation or absolute motion recovery. We propose splitting the range spectrum in three sub-bands to recover the unambiguous ionospheric difference with a linear problem; we interpret the solution of the linear system as the difference as a demodulation between an ambiguous and an unambiguous estimation of the ionosphere; and we analyse the performance of the proposed technique.