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Sensors 2017, 17(11), 2454; https://doi.org/10.3390/s17112454

Precise Aperture-Dependent Motion Compensation with Frequency Domain Fast Back-Projection Algorithm

1
School of Software, Xidian University, Xi’an 710071, China
2
National Laboratory of Radar Signal Processing, Collaborative Innovation Center of Information Sensing and Understanding, Xidian University, Xi’an 710071, China
3
Beijing Institute of Radio Measurement, The Second Academy of China Aerospace Science and Industry Corporation (CASIC), Beijing 100854, China
*
Authors to whom correspondence should be addressed.
Received: 20 August 2017 / Revised: 12 October 2017 / Accepted: 24 October 2017 / Published: 26 October 2017
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Abstract

Precise azimuth-variant motion compensation (MOCO) is an essential and difficult task for high-resolution synthetic aperture radar (SAR) imagery. In conventional post-filtering approaches, residual azimuth-variant motion errors are generally compensated through a set of spatial post-filters, where the coarse-focused image is segmented into overlapped blocks concerning the azimuth-dependent residual errors. However, image domain post-filtering approaches, such as precise topography- and aperture-dependent motion compensation algorithm (PTA), have difficulty of robustness in declining, when strong motion errors are involved in the coarse-focused image. In this case, in order to capture the complete motion blurring function within each image block, both the block size and the overlapped part need necessary extension leading to degeneration of efficiency and robustness inevitably. Herein, a frequency domain fast back-projection algorithm (FDFBPA) is introduced to deal with strong azimuth-variant motion errors. FDFBPA disposes of the azimuth-variant motion errors based on a precise azimuth spectrum expression in the azimuth wavenumber domain. First, a wavenumber domain sub-aperture processing strategy is introduced to accelerate computation. After that, the azimuth wavenumber spectrum is partitioned into a set of wavenumber blocks, and each block is formed into a sub-aperture coarse resolution image via the back-projection integral. Then, the sub-aperture images are straightforwardly fused together in azimuth wavenumber domain to obtain a full resolution image. Moreover, chirp-Z transform (CZT) is also introduced to implement the sub-aperture back-projection integral, increasing the efficiency of the algorithm. By disusing the image domain post-filtering strategy, robustness of the proposed algorithm is improved. Both simulation and real-measured data experiments demonstrate the effectiveness and superiority of the proposal. View Full-Text
Keywords: synthetic aperture radar (SAR); motion compensation (MOCO); frequency domain fast back-projection algorithm (FDFBPA); chirp-z transform (CZT) synthetic aperture radar (SAR); motion compensation (MOCO); frequency domain fast back-projection algorithm (FDFBPA); chirp-z transform (CZT)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Zhang, M.; Wang, G.; Zhang, L. Precise Aperture-Dependent Motion Compensation with Frequency Domain Fast Back-Projection Algorithm. Sensors 2017, 17, 2454.

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