“…The quality of the system imaging results completely depends on the accuracy of the GNSS system [19]. Later, Germany's MIRANDA35 system [19] and SUMATRA system [20], China's NUAA-MiniSAR [10], IECAS-SAR [9] are the first to use auto-focusing algorithm, such as map-drift (MD) [21], phase gradient auto-focus (PGA) [22], [23], and minimum entropy auto-focus (MEA) [24], which does not rely on inertial navigation system (INS) for high-resolution imaging. These auto-focusing algorithms have the disadvantages of only estimating the second-order error, requiring isolated feature points, and high computational complexity [25]- [27].…”