Improved specan algorithm based on Doppler rate equalization

The spectral analysis (SPECAN) algorithm is efficient and always used for synthetic aperture radar (SAR) data processing. But the azimuth dependence of Doppler rate is neglected in SPECAN algorithm, which results in the defocusing of targets away from the scene center. In order to solve this problem, an improved SPECAN algorithm is proposed. Considering the fact that the region of support in the azimuth frequency domain is different for targets in the same range gate, the algorithm equalizes the Doppler rate by nonlinear chirp scaling (NCS) in the azimuth frequency domain. Moreover, a modified map drift (MD) autofocus method is given to estimate the Doppler rate and its dependence. Finally, the effectiveness of the proposed algorithm is verified by real SAR data.