Widefield Parametric Polar Format Algorithm for Spotlight SAR Imaging.

For widefield synthetic aperture radar (SAR) imaging, range-dependent motion errors and range curvature are the main obstacle for range cell migration correction (RCMC) and azimuth focusing. The parametric polar format algorithm (PPFA) can handle the range-dependent motion errors after RCMC, but the nonsystem range cell migration is ignored. Furthermore, the residual range curvature is neglected, causing the undesired range cell migration. In this article, a novel widefield PPFA is developed for widefield spotlight SAR imaging. A precise range-compressed domain motion compensation algorithm is introduced for the range-dependent motion errors. It can precisely compensate for the range-dependent motion errors before RCMC. After RCMC, an accurate range curvature correction algorithm is carried out, accelerated by the scaling Fourier transform. Based on these improvements, an azimuth wavenumber resampling integrating azimuth-variant phase error compensation is implemented to achieve well-focused images. Finally, extensive simulated and real-measured SAR data have validated the algorithm's effectiveness.