The spatial resolution of an imaging system is a key factor, which steers its performance for complex target detection, characterization and recognition. Active electromagnetic imaging systems with limited frequency bandwidth and synthetic aperture may fail to discriminate important details during the imaging process, due to their insufficient resolution properties. Spectral estimation methods may be used to overcome such limitations through dedicated signal processing techniques. This study proposes a new signal processing chain, which is able to cope with near-field and wide-band configurations, to significantly improve 2-D resolution, using classical spectral estimation methods. This work is based on an efficient handling and compensation of critical signal properties, such as near-field and wide bandwidths, which make the proposed technique able to deal with very general imaging configurations, such as near/far-ranges, narrow/wide-beamwidths and -bandwidths, very short aperture... Experimental results obtained at millimeter-wave are shown to demonstrate the performance and versatility of the proposed approach.
2. Ulander, L. M. H., H. Hellsten, and G. Stenstrom, "Synthetic-aperture radar processing using fast factorized back-projection," IEEE Transactions on Aerospace and Electronic Systems, Vol. 39, No. 3, 760-776, Jul. 2003.
3. Rocca, F., "Synthetic aperture radar: A new application for wave equation techniques," Stanford Exploration Project, Vol. 56, 167-189, 1987.
4. Cafforio, C., C. Prati, and F. Rocca, "SAR data focusing using seismic migration techniques," IEEE Transactions on Aerospace and Electronic Systems, Vol. 27, No. 2, 194-207, Mar. 1991.
5. Milman, A., "SAR imaging by ωκ migration," International Journal of Remote Sensing, Vol. 14, No. 10, 1965-1979, 1993.
6. Caorsi, S., M. Donelli, A. Lommi, and A. Massa, "Location and imaging of two-dimensional scatterers by using a particle swarm algorithm," Journal of Electromagnetic Waves and Applications, Vol. 18, No. 4, 481-494, 2004.
7. Kay, S. M. and S. L. Marple, "Spectrum analysisa modern perspective," Proceedings of the IEEE, Vol. 69, No. 11, 1380-1419, 1981.
8. Stoica, P., et al., Spectral Analysis of Signals, Vol. 452, Pearson Prentice Hall, Upper Saddle River, NJ, 2005.
9. Nehorai, A. and E. Paldi, "Vector-sensor array processing for electromagnetic source localization," IEEE Transactions on Signal Processing, Vol. 42, No. 2, 376-398, 1994.
10. Krim, H. and M. Viberg, "Two decades of array signal processing research: The parametric approach," IEEE Signal Processing Magazine, Vol. 13, No. 4, 67-94, 1996.
11. Azimi-Sadjadi, M. R., A. Pezeshki, and N. Roseveare, "Wideband doa estimation algorithms for multiple moving sources using unattended acoustic sensors," IEEE Transactions on Aerospace and Electronic Systems, Vol. 44, No. 4, 1585-1599, Oct. 2008.
12. Chen, J. C., R. E. Hudson, and K. Yao, "Maximum-likelihood source localization and unknown sensor location estimation for wideband signals in the near-field," IEEE Transactions on Signal Processing, Vol. 50, No. 8, 1843-1854, Aug. 2002.
13. Tung, T. L., K. Yao, D. Chen, R. E. Hudson, and C. W. Reed, "Source localization and spatial filtering using wideband music and maximum power beamforming for multimedia applications," 1999 IEEE Workshop on Signal Processing Systems, SiPS 99, Design and Implementation (Cat. No. 99TH8461), 625-634, 1999.
14. Chen, J. C., K. Yao, and R. E. Hudson, "Source localization and beamforming," IEEE Signal Processing Magazine, Vol. 19, No. 2, 30-39, Mar. 2002.
15. Grosicki, E., K. Abed-Meraim, and Y. Hua, "A weighted linear prediction method for near-field source localization," IEEE Transactions on Signal Processing, Vol. 53, No. 10, 3651-3660, Oct. 2005.
16. Krolik, J. and D. Swingler, "Focused wide-band array processing by spatial resampling," IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 38, No. 2, 356-360, 1990.
17. Lo, K. W., "Adaptive array processing for wide-band active sonars," IEEE Journal of Oceanic Engineering, Vol. 29, No. 3, 837-846, 2004.
18. Huang, Y.-D. and M. Barkat, "Near-field multiple source localization by passive sensor array," IEEE Transactions on Antennas and Propagation, Vol. 39, No. 7, 968-975, 1991.
19. Chen, J. C., R. E. Hudson, and K. Yao, "Maximum-likelihood source localization and unknown sensor location estimation for wideband signals in the near-field," IEEE Transactions on Signal Processing, Vol. 50, No. 8, 1843-1854, 2002.
20. Zhi, W. and M. Y.-W. Chia, "Near-field source localization via symmetric subarrays," IEEE International Conference on Acoustics, Speech and Signal Processing, 2007, ICASSP 2007, Vol. 2, II–1121, IEEE, 2007.
21. De Graaf, S. R., "SAR imaging via modern 2-D spectral estimation methods," IEEE Transactions on Image Processing, Vol. 7, No. 5, 729-761, 1998.
22. Li, J. and P. Stoica, "An adaptive filtering approach to spectral estimation and SAR imaging," IEEE Transactions on Signal Processing, Vol. 44, No. 6, 1469-1484, 1996.
23. Benitz, G. R., "High-definition vector imaging," Lincoln Laboratory Journal, Vol. 10, No. 2, 147-170, 1997.
24. Cetin, M. and W. C. Karl, "Feature-enhanced synthetic aperture radar image formation based on nonquadratic regularization," IEEE Transactions on Image Processing, Vol. 10, No. 4, 623-631, 2001.
25. Jakowatz, C. V., D. E. Wahl, P. H. Eichel, D. C. Ghiglia, and P. A. Thompson, "Spotlight-mode synthetic aperture radar: A Signal processing approach," Springer Science & Business Media, 2012.
26. Tomiyasu, K., "Conceptual performance of a satellite borne, wide swath synthetic aperture radar," IEEE Transactions on Geoscience and Remote Sensing, No. 2, 108-116, 1981.
27. Schmidt, R., "Multiple emitter location and signal parameter estimation," IEEE Transactions on Antennas and Propagation, Vol. 34, No. 3, 276-280, 1986.
28. Shan, T.-J., M. Wax, and T. Kailath, "On spatial smoothing for direction-of-arrival estimation of coherent signals," IEEE Transactions on Acoustics, Speech, and Signal Processing, Vol. 33, No. 4, 806-811, 1985.
29. Huang, Y., L. Ferro-Famil, and A. Reigber, "Under-foliage object imaging using SAR tomography and polarimetric spectral estimators," IEEE Transactions on Geoscience and Remote Sensing, Vol. 50, No. 6, 2213-2225, 2012.
30. Sauer, S., L. Ferro-Famil, A. Reigber, and E. Pottier, "Three-dimensional imaging and scattering mechanism estimation over urban scenes using dual-baseline polarimetric insar observations at L-band," IEEE Transactions on Geoscience and Remote Sensing, Vol. 49, No. 11, 4616-4629, 2011.
31. Capon, J., "High-resolution frequency-wavenumber spectrum analysis," Proceedings of the IEEE, Vol. 57, No. 8, 1408-1418, 1969.
32. Akaike, H., "A new look at the statistical model identification," IEEE Transactions on Automatic Control, Vol. 19, No. 6, 716-723, Dec. 1974.
33. McClellan, J. H., "Multidimensional spectral estimation," Proceedings of the IEEE, Vol. 70, No. 9, 1029-1039, 1982.
34. Jakobsson, A., S. L. Marple, and P. Stoicav, "Computationally efficient two-dimensional capon spectrum analysis," IEEE Transactions on Signal Processing, Vol. 48, No. 9, 2651-2661, 2000.