Focusing Improvement for Ground Moving Target in High-Squint Synthetic Aperture Radar Imagery

For desired resolution, high-squint SAR has a large coherent processing interval (CPI). In this case, the high signal-to-clutter ratio (SCR) echo of moving target can not be guaranteed due to the presence of ground clutter, and the maneuvering motion of moving target usually causes high-order phase terms, which can not be neglected for precise focusing. In this paper, the climb method is applied to the range-compressed echo containing moving target to improve the SCR. For the subsequent focusing, we assume that the target of interest has constant velocity in subaperture CPI, but maneuvering motion parameters for the whole CPI. Within the short subaperture CPI, the target signal can be simplified as a three-order polynomial function with the unknown coefficients to be estimated by some time-frequency analysis tools, including Hough transform and fractional Fourier transform. Then the subaperture Doppler parameters are combined to form a total least square problem, outputting the high-order phase terms. The effectiveness of the proposed GMTIm method is validated by real-measured high-squint SAR data.