Autofocus for correcting three dimensional trajectory deviations in synthetic aperture radar

The back-projection (BP) algorithm is an ideal solution for airborne synthetic aperture radar (SAR) imaging. However, trajectory deviations degrade BP focusing performance dramatically due to the accuracy limitation of navigation system. In this paper, we propose a novel autofocus method compatible with the BP imagery, which can correct the 3D trajectory deviations. In the new method, multiple local images at different illumination directions within the radar beam are synthesized to trace the local phase gradient. From these phase gradient estimates, accurate trajectory update can be achieved. Experiment based on highly squinted SAR data validates the effectiveness of the proposed autofocus method.