A novel autofocus algorithm for spaceborne Synthetic Aperture Radar Imaging

The Doppler parameters are the most important parameter in spaceborne Synthetic Aperture Radar (SAR) imaging. This paper analyzed the basic principle of Doppler frequency rate estimation and proposed a new estimation algorithm called Mean Frequency Shift Correlation (MFSC) algorithm for Doppler frequency rate. At first, the basic mean is obtained via system parameters, then the adjustable value of every range gate is obtained through shift and correlation method, finally basic mean together with adjustable value of every range gate is Doppler frequency rate of each range gate. The MFSC is different with image domain ago, and it begins with data domain directly and doesn't need iterative calculation. So it reduces operations and time of estimation and improves the estimated precision; at the same time, the adaptability for terrain is very strong. Finally, the raw data of ERS-2 are used to test effectiveness and feasibility of this method. The results of imaging with raw data are presented to verify the validity of the approach.