The coherence between the complex image pair from two channels is important for improving the capability of along-track interferometry (ATI) processing in synthetic aperture radar (SAR) ground moving target indication (GMTI). The along-track dual-channel low frequency SAR can be easily influenced by not only mismatch errors of the image pair but also the radio frequency interference (RFI). RFI has great impacts on the joint probability density function (PDF) of magnitude and phase in the interferometric image. However, little work has been done to investigate the coherence improvement under RFI. This study develops an algorithm to improve the coherence of the image pair for along-track dual-channel low frequency SAR, which can be used by ATI. After analyzing RFI imaging in detail, it is proposed that the along-track interferometric image in the range frequency and cross-range slow time domain can be used to detect RFI. Median filters are proposed to further suppress RFI. This suppression has the same implementations to the image pair without heavy computation load. Considering RFI suppression and mismatch errors compensation, a pre-processing flow is proposed to achieve high coherence of the interferometric image in low frequency SAR. It is shown that the coherence of the complex image pair can be improved greatly by using this pre-processing flow. The effectiveness of this algorithm is demonstrated with real data acquired by an airborne along-track dual-channel P-band SAR GMTI system.
2. Chan, Y. K. and V. C. Koo, "An introduction to synthetic aperture radar (SAR)," Progress In Electromagnetics Research B, Vol. 2, 27-60, 2008.
3. Mao, X. H., D. Y. Zhu, L. Ding, and Z. D. Zhu, "Comparative study of RMA and PFA on their responses to moving target," Progress In Electromagnetics Research, Vol. 110, 103-124, 2010.
4. Chang, Y.-L., C.-Y. Chiang, and K.-S. Chen, "SAR image simulation with application to target recognition," Progress In Electromagnetics Research, Vol. 119, 35-57, 2011.
5. Ma, L., Z. F. Li, and G. S. Liao, "System error analysis and calibration methods for multi-channel SAR," Progress In Electromagnetics Research, Vol. 112, 309-327, 2011.
6. Xu, W. and Y. K. Deng, "Investigation on electronic azimuth beam steering in the spaceborne SAR imaging modes," Journal of Electromagnetic Waves and Applications, Vol. 25, No. 14-15, 2076-2088, 2011.
7. Umrani, A. W., "Effect of steering error vector and angular power distributions on beamforming and transmit diversity systems in correlated fading channel," Progress In Electromagnetics Research, Vol. 105, 383-402, 2010.
8. Wang, T., Z. Bao, Z. Zhang, and J. Ding, "Improving coherence of complex image pairs obtained by along-track bistatic SARs using range-azimuth prefitering," IEEE Transactions on Geoscience and Remote Sensing, Vol. 46, No. 1, 3-13, 2008.
9. Lv, X., M. Xing, Z. Bao, S. Zhang, and Y. Wu, "Coherence improving algorithm for airborne multichannel SAR-GMTI," IET Radar Sonar and Navigation, Vol. 4, No. 3, 336-347, 2010.
10. Vu, V. T., T. K. Sjogren, M. I. Pettersson, H. J. Zepernick, and A. Gustavsson, "Experimental results on moving target detection by focusing in UWB low frequency SAR," 2007 IET International Conference on Radar Systems, 1-5, Huangshan, China,2007.
11. Yang, J., X. Huang, J. Thompson, T. Jin, and Z. Zhou, "Low frequency UWB SAR ground moving target imaging," IET Radar,Sonar & Navigation,, Vol. 5, No. 9, 994-1001, 2011.
12. Du, Y., Y. L. Luo, W. Z. Yan, and J. A. Kong, "An electromagnetic scattering model for soybean canopy," Progress In Electromagnetics Research, Vol. 79, 209-223, 2008.
13. Chen, J., S. Quegan, and X. J. Yin, "Calibration of spaceborne linearly polarized low frequency SAR using polarimetric selective radar calibrators," Progress In Electromagnetics Research, Vol. 114, 89-111, 2011.
14. Miller, T., L. Potter, and J. McCorkle, "RFI suppression for ultra wideband radar," IEEE Transactions on Aerospace and Electronic Systems, Vol. 33, No. 4, 1142-1156, 1997.
15. Liu, Q., S. Xing, X. Wang, J. Dong, D. Dai, and Y. Li, "The interferometry phase of InSAR coherent jamming with arbitrary waveform modulation," Progress In Electromagnetics Research, Vol. 124, 101-118, 2012.
16. Liu, Q. F., S.-Q. Xing, X.-S. Wang, J. Dong, D.-H. Dai, and Y.-Z. Li, "The "SLOPE" effect of coherent transponder in InSAR DEM," Progress In Electromagnetics Research, Vol. 127, 351-370, 2012.
17. Potsis, A., A. Reigber, and K. P. Papathanassiou, "A phase preserving method for RF interference suppression in P-band synthetic aperture radar interferometric data," IEEE IGARSS'99, 2655-2657, Hamburg, Germany,1999.
18. Reigber, A. and L. Ferro-Famil, "Interference suppression in synthesized SAR images," IEEE Geoscience and Remote Sensing Letters, Vol. 2, No. 1, 45-49, 2005.
19. Vu, V. T., X. Sjögren, T. K. Gren, M. I. Pettersson, L. Håkansson,A. Gustavsson, and L. M. H. Ulander, "RFI suppression in ultrawideband SAR using an adaptive line enhancer," IEEE Geoscience and Remote Sensing Letters, Vol. 7, No. 4, 694-698, 2010.
20. Tian, J., Z. Zhimin, and S. Qian, "Subaperture wiener filter construction for time-varying RFI suppression in UWB SAR," 1st Asian and Pacific Conference on Synthetic Aperture Radar, 2007,APSAR 2007,71-75, 2007.
21. Dong, Z., D. Liang, and X. Huang, "A RFI suppression algorithm based on channel equalization for the VHF/UHF UWB SAR," Journal Electronics & Information Technology, Vol. 30, No. 3, 550-553, 2008.
22. Rosen, P. A., S. Hensley, and C. Le, "Observations and mitigation of RFI in ALOS PALSAR SAR data: Implications for the DESDYNI mission," IEEE Radar Conference, 2008, Radar'08,1-6, Rome, Italy,2008.
23. Gierull, C. H., "Digital channel balancing of along-track interferometric SAR data," DRDC, Canada, Ottawa,2003.
24. Ren, S., W. Chang, T. Jin, and Z. Wang, "Automated sar reference image preparation for navigation," Progress In Electromagnetics Research, Vol. 121, 535-555, 2011.
25. Koo, V. C., Y. K. Chan, V. Gobi, M. Y. Chua, C. H. Lim, C.-S. Lim, C. C. Thum, T. S. Lim, Z. Bin Ahmad, K. A. Mahmood,M. H. Bin Shahid, C. Y.Ang, W. Q. Tan, P. N. Tan, K. S. Yee,W. G. Cheaw, H. S. Boey, A. L. Choo, and B. C. Sew, "A new unmanned aerial vehicle synthetic aperture radar for environmental monitoring," Progress In Electromagnetics Research, Vol. 122, 245-268, 2012.
26. Chua, M. Y. and V. C. Koo, "FPGA-based chirp generator for high resolution UAV SAR," Progress In Electromagnetics Research, Vol. 99, 71-88, 2009.
27. Gierull, C. H., "Statistical analysis of multilook SAR interfer ograms for CFAR detection of ground moving targets," IEEE Transactions on Geoscience and Remote Sensing, Vol. 42, No. 4, 691-701, 2004.
28. Cumming, I. G. and F. H. Wong, Digital Processing of Synthetic Aperture Radar Data: Algorithms and Implementation, Artech House Inc., Norwood, MA, USA,2005.
29. An, D. X., Z.-M. Zhou, X.-T. Huang, and T. Jin, "A novel imaging approach for high resolution squinted spotlight SAR based on the deramping-based technique and azimuth NLCS principle," Progress In Electromagnetics Research, Vol. 123, 485-508, 2012.
30. Capozzoli, A., C. Curcio, and A. Liseno, "GPU-based ω-k tomographic processing by 1D non-uniform FFTs," Progress In Electromagnetics Research M, Vol. 23, 279-298, 2012.
31. Kay, S. M., Modern Spectral Estimation: Theory and Application, Prentice Hall, Englewood Cliffs, NJ, USA, 1988.
32. Fan, C. Y., X. T. Huang, Z. L. Xu, and T. Jin, "A RFI suppression approach based on along-track interferometric image," 2011 IEEE CIE International Conference on Radar, Vol. 1, 214-218, Chengdu, China, 2011.
33. Sekretarov, S. and D. M. Vavriv, "A wideband slotted waveguide antenna array for SAR system," Progress In Electromagnetics Research M, Vol. 11, 165-176, 2010.
34. Habib, M. A., A. Bostani, A. Djaiz, M. Nedil, M. C. E. Yagoub,and T. A. Denidni, "Ultra wideband CPW-FED aperture antenna with WLAN band rejection," Progress In Electromagnetics Research, Vol. 106, 17-31, 2010.
35. Chen, A., T. Jiang, Z. Chen, and D. Su, "A novel low-profile wideband UHF antenna," Progress In Electromagnetics Research, Vol. 121, 75-88, 2011.
36. Li, S., H.-P. Xu, and L. Q. Zhang, "An advanced DSS-SAR InSAR terrain height estimation approach based on baseline decoupling," Progress In Electromagnetics Research, Vol. 119, 207-224, 2011.
37. Feng, L., H. P. Xu, C. S. Li, S. Li, and H. Gao, "A novel estimation approach of dynamic and coupling baseline for distributed satellite SAR," Progress In Electromagnetics Research, Vol. 123, 467-484, 2012.
38. Woo, J.-C., B.-G. Lim, and Y.-S. Kim, "Modification of the recursive sidelobe minimization technique for the range-Doppler algorithm of SAR imaging," Journal of Electromagnetic Waves and Applications, Vol. 25, No. 13, 1783-1794, 2011.
39. Lei, P. Z., H. Zhou, and X. T. Huang, "Multi-channel equalization for SAR/GMTI system with small time-bandwidth chirp signal," 2011 IEEE CIE International Conference on Radar, Vol. 1, 707-710, Chengdu, China,2011.