An Improved Phase Gradient Autofocus Algorithm Used in Real-time Processing
Qing Ji-ming①② Xu Hao-yu③ Liang Xing-dong① Li Yan-lei①
①(National Key Laboratory of Science and Technology on Microwave Imaging, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China) ②(University of Chinese Academy of Sciences, Beijing 100049, China) ③(Shanghai Advanced Researched Institute, University of Chinese Academy of Sciences, Shanghai 201203, China)
The Phase Gradient Autofocus (PGA) algorithm can remove the high order phase error effectively, which is of great significance to get high resolution images in real-time processing. While PGA usually needs iteration, which necessitates long working hours. In addition, the performances of the algorithm are not stable in different scene applications. This severely constrains the application of PGA in real-time processing. Isolated scatter selection and windowing are two important algorithmic steps of Phase Gradient Autofocus Algorithm. Therefore, this paper presents an isolated scatter selection method based on sample mean and a windowing method based on pulse envelope. These two methods are highly adaptable to data, which would make the algorithm obtain better stability and need less iteration. The adaptability of the improved PGA is demonstrated with the experimental results of real radar data.
田雪, 梁兴东, 李焱磊, 等. 基于子孔径包络误差校正的SAR高精度运动补偿方法[J]. 雷达学报, 2014, 3(5): 583-590. Tian Xue, Liang Xing-dong, Li Yan-lei, et al.. High-precision motion compensation method based on the subaperture envelope error correction for SAR[J]. Journal of Radars, 2014, 3(5): 583-590.
[2]
张磊, 邓云凯, 王宇, 等. 基于代价函数的通道误差校正方法[J]. 雷达学报, 2014, 3(5): 556-564. Zhang Lei, Deng Yun-kai, Wang Yu, et al.. Channel error compensation for multi-channel sar based on cost function[J]. Journal of Radars, 2014, 3(5): 556-564.
[3]
高阳, 禹卫东, 冯锦, 等. 一种基于勒让德拟合的SAR后向投影自聚焦算法[J]. 雷达学报, 2014, 3(2): 176-182. Gao Yang, Yu Wei-dong, Feng Jin, et al.. A SAR back projection autofocusing algorithm based on legendre approximation[J]. Journal of Radars, 2014, 3(2): 176-182.
[4]
折小强, 仇晓兰, 韩冰, 等. 一种基于变换域的滑动聚束SAR调频率估计方法[J]. 雷达学报, 2014, 3(4): 419-427. She Xiao-qiang, Qiu Xiao-lan, Han Bing, et al.. An improved doppler rate estimation approach for sliding spotlight sar data based on the transposition domain[J]. Journal of Radars, 2014, 3(4): 419-427.
[5]
张新, 丁赤飚, 吴一戎, 等. 一种用于条带式RD算法的组合实时PGA方法[J]. 电子与信息学报, 2007, 29(5): 1065-1068. Zhang Xin, Ding Chi-biao, Wu Yi-rong, et al.. A combined real time PGA method for strip map airborne SAR with RD algorithm[J]. Journal of Electronics & Information Technology, 2007, 29(5): 1065-1068.
[6]
Yadin E. SAR autofocusing viewed as adaptive beamforming on prominent scatters[C]. Record of 1994 IEEE National Radar Conference, Atlanta GA, 1994: 138-143.
[7]
李燕平, 邢孟道, 保铮. 一种改进的相位梯度自聚焦方法[J]. 西安电子科技大学学报(自然科学版), 2007, 34(3): 386-391. Li Yan-ping, Xing Meng-dao, and Bao Zheng. Improved phase gradient autofocus algorithm based on adaptive isolated scatter selection[J]. Journal of Xidian University, 2007, 34(3): 386-391.
[8]
Fu Tuo, Gao Mei-guo, and He Yuan. An improved scatter selection method for phase gradient autofocus algorithm in SAR/ISAR autofocus[C]. Proceedings of the 2003 International Conference on Neural Networks and Signal Processing, Nanjing, China, 2003: 1054-1057.
[9]
Wahl D E, Eichel P H, and Ghiglia D C. Phase gradient autofocus - a robust tool for high resolution SAR phase correction[J]. IEEE Transactions on Aerospace and Electionic Systems, 1994, 30(3): 827-835.
[10]
倪崇, 王岩飞, 徐向辉, 等. 一种改进的SAR图像聚焦方法[J]. 测绘学报, 2012, 41(3): 449-453. Ni Chong, Wang Yan-fei, Xu Xiang-hui, et al.. An improved autofocus algorithm for SAR images[J]. Acta Geodaetica et Cartographica Sinica, 2012, 41(3): 449-453.
[11]
林格, 刘明敬, 郝明. 改进的相位梯度自聚焦加窗方法[J]. 信息化研究, 2010, 36(7): 25-28. Lin Ge, Liu Ming-jing, and Hao Ming. Improved windowing method for phase gradient autofocus algorithm[J]. Informatization Research, 2010, 36(7): 25-28.
[12]
闫龙, 郑妍, 李颜超. 改进的机载SAR相位梯度自聚焦算法[J]. 应用科技, 2012, 39(1): 39-43. Yan Long, Zheng Yan, and Li Yan-chao. Improved algorithm of phase gradient autofocus for air-borne synthetic aperture radar[J]. Applied Science and Technology, 2012, 39(1): 39-43.
[13]
李建阳, 常文革, 王亮. 一种应用于条带SAR的改进PGA算法[J]. 现代雷达, 2007, 29(8): 52-55. Li Jian-yang, Chang Wen-ge, and Wang Liang. A modified PGA algorithm used in stripmap SAR[J]. Modern Radar, 2007, 29(8): 52-55.
[14]
Zhu Dai-yin, Jiang Rui, and Mao Xin-hua. Multi-Subaperture PGA for SAR autofocusing[J]. IEEE Transactions on Aerospace and Electionic Systems, 2013, 49(1): 468-488.
[15]
Thompson D G, Bates J S, and Arnold D V. Extending the phase gradient autofocus algorithm for low-altitude Stripmap mode SAR[C]. Proceedings of the 1999 IEEE Radar Conference, Waltham, MA, 1999: 36-40.
[16]
蒋锐, 朱岱寅, 朱兆达. 一种用于条带模式SAR成像的自聚焦算法[J]. 航空学报, 2010, 31(12): 2385-2392. Jiang Rui, Zhu Dai-yin, and Zhu Zhao-da. A novel approach to strip-map SAR autofocus[J]. Acta Aeronautica et Astronautica Sinica, 2010, 31(12): 2385-2392.
[17]
孟大地, 丁赤飚. 一种用于条带式SAR的自聚焦算法[J]. 电子与信息学报, 2005, 27(9): 1349-1352. Meng Da-di and Ding Chi-biao. A new approach to autofocus considering strip map SAR[J]. Journal of Electronics & Information Technology, 2005, 27(9): 1349-1352.
[18]
Wahl D E, Jakowatz Jr, C V, and Thompson P A. New approach to Strip-Map SAR autofocus[C]. 1994 Sixth IEEE Digital Signal Processing Workshop, Yosemite National Park, 1994: 53-56.
[19]
Eichel P H, Ghiglia D C, and Jakowatz C V. Speckle processing method for synthetic-aperture-radar phase correction[J]. Optics Letters, 1989, 14(1): 1-3.
[20]
Fienup J R. Phase error correction by shear averaging[C]. Signal Recovery and Synthesis II, Optical Society of America, 1989: 134-137.
2015, Vol. 4 
