Fast back-projection autofocus for linear array SAR 3-D imaging via maximum sharpness

Autofocusing technique is an indispensable step for linear array SAR (LASAR) three-dimensional (3-D) high quality imaging. However, the existing autofocus methods used for LASAR usually suffer from low accuracy or heavy computation burden, due to the non-uniform antenna phase centers (APC) and the huge data of LASAR. In this paper, a novel fast back-projection autofocusing algorithm via maximum sharpness (BP-FMSA), is proposed for LASAR 3-D autofocus imaging. In the scheme, the autofocus model via maximum sharpness back-projection is constructed, and the expression of phase error estimation is derived. Then, the conjugate gradient method is introduced to efficiency estimate the phase errors of LASAR. Moreover, to further improve the computing efficiency of BP-FMSA, only the area consisted by dominant scatterers are selected as the input of sharpness estimation. The effectiveness of the algorithm is demonstrated with both simulation and experimental examples.