Extended Polar Format Algorithm for Non-Planar Target Imaging With DSM

In case of circular or non-linear acquisition trajectory, synthetic aperture radar (SAR) focusing becomes increasingly sensitive to elevation. For non-planar target imaging, it not only appears fore-shortening but also blurred. As the wider integration angle and higher elevation of objects, the defocus cannot be ignored. Generally, the polar format algorithm (PFA) is an efficient imaging algorithm for circular or non-linear SAR. However, in the process of PFA, the impact of focusing at an incorrect altitude has not been considered. In this article, the conventional PFA is adapted to incorporate the known digital surface model (DSM) into the imaging process. Firstly, the maximum allowable elevation deviation (MAED) $\delta {{z}_{\max }}$ is derived. Secondly, for non-planar targets that are higher than $\delta {{z}_{\max }}$, data extraction is applied in the range-Doppler domain. Additionally, a compensation function is multiplied, which is constructed based on DSM data separately. The corresponding original echo data is then replaced with the processed data. The whole method only involves fast Fourier transform (FFT) and complex multiplication which enhances operational efficiency. The simulated and experimental data results demonstrated the effectiveness and practicability of the proposed algorithm.