Two-stage autofocus algorithm with filled function for synthetic aperture radar

Abstract. Entropy-based parametric autofocus is commonly applied to correct the residual azimuth phase error (APE) that arises from the residual motion errors (RME) in synthetic aperture radar. However, the image’s entropy trends to a convex function only when a great number of range bins are selected according to the law of large numbers, which means that the average residual APE is finally obtained via this method for the space-variant characteristics of RME. A two-stage parametric autofocus algorithm is carried out to derive the exact residual APE with several range bins selected for iteration. To this end, a new objective function in the first stage is designed to reduce the number of local solutions and protect targets from energy leaking. In the second stage, the filled function is imported to jump out of the current solution to a more optimal one until no other optimal solution exists. In the final part, both simulated and real data experiments validate the performance of the proposed method.

[1]  R. Ge,et al.  A class of filled functions for finding global minimizers of a function of several variables , 1987 .

[2]  Giorgio Franceschetti,et al.  A SAR processor based on two-dimensional FFT codes , 1990 .

[3]  Charles V. Jakowatz,et al.  Phase gradient autofocus-a robust tool for high resolution SAR phase correction , 1994 .

[4]  G. Donohoe,et al.  Subaperture autofocus for synthetic aperture radar , 1994 .

[5]  Tat Soon Yeo,et al.  Noniterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery , 1998, IEEE Trans. Geosci. Remote. Sens..

[6]  David G. Long,et al.  Extending the phase gradient autofocus algorithm for low-altitude stripmap mode SAR , 1999, IEEE 1999 International Geoscience and Remote Sensing Symposium. IGARSS'99 (Cat. No.99CH36293).

[7]  Stefano Lucidi,et al.  New Classes of Globally Convexized Filled Functions for Global Optimization , 2002, J. Glob. Optim..

[8]  Ian G. Cumming,et al.  Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation , 2005 .

[9]  Junfeng Wang,et al.  SAR Minimum-Entropy Autofocus Using an Adaptive-Order Polynomial Model , 2006, IEEE Geoscience and Remote Sensing Letters.

[10]  Timothy J. Schulz,et al.  Optimal Sharpness Function for SAR Autofocus , 2007, IEEE Signal Processing Letters.

[11]  Alberto Moreira,et al.  An Autofocus Approach for Residual Motion Errors With Application to Airborne Repeat-Pass SAR Interferometry , 2008, IEEE Transactions on Geoscience and Remote Sensing.

[12]  Zhifeng Dai,et al.  Global convergence of a modified Hestenes-Stiefel nonlinear conjugate gradient method with Armijo line search , 2011, Numerical Algorithms.

[13]  I. Hajnsek,et al.  A tutorial on synthetic aperture radar , 2013, IEEE Geoscience and Remote Sensing Magazine.

[14]  Xinhua Mao,et al.  Multi-Subaperture PGA for SAR Autofocusing , 2013, IEEE Transactions on Aerospace and Electronic Systems.

[15]  F. Li,et al.  SAR Image Autofocus Utilizing Minimum-Entropy Criterion , 2013, IEEE Geoscience and Remote Sensing Letters.

[16]  Wei Song,et al.  Comparison of two-step and one-step motion compensation algorithms for airborne synthetic aperture radar , 2015 .

[17]  Zhimin Zhang,et al.  Extension and Evaluation of PGA in ScanSAR Mode using Full-Aperture Approach , 2015, IEEE Geoscience and Remote Sensing Letters.

[18]  Yong Wang,et al.  Enhancement of Azimuth Focus Performance in High-Resolution SAR Imaging Based on the Compensation for Sensors Platform Vibration , 2016, IEEE Sensors Journal.

[19]  Jinping Sun,et al.  High-frequency vibration compensation of helicopter-borne THz-SAR [Correspondence] , 2016, IEEE Transactions on Aerospace and Electronic Systems.

[20]  Xingzhao Liu,et al.  Range- and Aperture-Dependent Motion Compensation Based on Precise Frequency Division and Chirp Scaling for Synthetic Aperture Radar , 2019, IEEE Sensors Journal.