An Autofocus Algorithm for TOPS Mode BP SAR Image Based on Spectrum Compression

In the high squint TOPS mode SAR imaging by using the BP imaging algorithm in the rectangular coordinate system of the ground plane, the wide swath SAR image without distortion in the ground plane can be obtained in a short time. However, how to quickly complete the motion error compensation of the BP image is still a difficulty in practical application. This paper proposes an improved spectrum compression method, which can quickly realize the follow-up operations such as autofocus of the BP image of the ground plane in the high squint TOPS mode of the mobile platform. Firstly, considering that the traditional BP spectrum compression method is only applicable to the spotlight imaging mode, combined with the virtual rotation center theory of high-squint TOPS SAR and the wavenumber spectrum analysis, an improved exact spectrum compression function is derived, which can obtain the unambiguous ground plane TOPS mode BP image spectrum through full-aperture compression. On this basis, the phase gradient autofocus (PGA) can be used to quickly complete the full aperture motion error estimation and compensation. Finally, the effectiveness of the proposed algorithm is verified by simulation data processing.