Map-drift Autofocus and Scene Stabilization for Video-SAR

Onboard video-SAR systems are susceptible to blurring due to motion measurement errors during the integration time required to process each frame. Established techniques like Phase Gradient Autofocus can render sharp video but need to have the azimuth dimension aligned with one of the axes of each frame. Video-SAR systems that use backprojection typically take advantage of sub-aperture processing and form images on a fixed ground coordinate system. As such the azimuth dimension rotates through the frames according to the aspect angle of the radar. For these cases we have extended the concept of map-drift to video-SAR by registering sub-images to the aperture center sub-image before coherently accumulating them into a fully resolved image. Furthermore, inter-frame drift caused by the motion measurement system can be measured by means of a cross-correlation operation and fed back to the image formation process or motion measurement system in order to stabilize the ground reference point.