The effect of polar format resampling on uncompensated motion phase errors and the phase gradient autofocus algorithm

The phase gradient algorithm (PGA) is an autofocus technique applied after SAR image formation for correcting uncompensated motion phase errors. A crucial aspect of the algorithm is the assumed phase error model used to describe the motion errors in the phase history data. In this paper it is shown that the Polar Format Algorithm (PFA) image formation processor introduces a distortion to the phase error that is not considered in the PGA formulation. It is shown that the PFA distortions degrade the point target response in the PGA image output and act as a source of relative phase errors in repeat pass SAR interferometry applications.