Presence of phase errors in radar data is a crucial problem for high-resolution SAR imaging. In the paper, a new idea for representation of an arbitrary phase error by its local approximations is proposed. Within such approach, a general analytical expression for the resolution degradation of multi-look SAR images is derived. The principle of local approximations is also used in a novel autofocusing approach that allows estimating and compensating of an arbitrary residual phase error function via measuring local quadratic phase errors.

Residual Phase Errors and Autofocusing in Airborne SAR Systems