Abstract
Bistatic Synthetic Aperture Radar (SAR) has attracted increasing attention in recent years due to its unique advantages, such as the ability of forward-looking imaging. In translational variant bistatic forward-looking SAR (TV-BFSAR), it is difficult to get a well focused image due to large range cell migration (RCM) and 2-D variation of both Doppler characteristics and RCM. In this paper, an extended azimuth nonlinear chirp scaling (NLCS) algorithm is proposed to deal with these problems. Firstly, Keystone Transform (KT) is introduced to remove the spatial-variant linear RCM, which is of great significance in TV-BFSAR. Secondly, a correction factor is multiplied to the signal in range frequency domain to compensate for the residual RCM. At last, a fourth-order filtering together with azimuth NLCS is performed in every range gate to equalize both the azimuth-variant Doppler centroid and frequency modulation rate based on the azimuth numerical fitting. The proposed method is verified by simulation and real data processing. Multiple targets are generated and focused by the method, of which the peak sidelobe ratio (PSLR) is around −13 dB and integrated sidelobe ratio (ISLR) is around −10 dB. The method is accurate and can achieve high-resolution focusing for TV-BFSAR data.
Highlights
In recent years, synthetic aperture radar (SAR) has become increasingly attractive in both civilian and military fields, because it can provide high-resolution day- and night-time images of the observed area, independent of weather conditions [1,2,3,4]
We can construct a phase factor in the time domain to compensate for the residual range cell migration (RCM), which is given by φRCMC = exp − jπ
The algorithm can be grouped into two parts: the range range cell migration correction (RCMC) and azimuth extended nonlinear chirp scaling (NLCS)
Summary
Synthetic aperture radar (SAR) has become increasingly attractive in both civilian and military fields, because it can provide high-resolution day- and night-time images of the observed area, independent of weather conditions [1,2,3,4]. First-order KT has already been applied to the stationary scene data processing of bistatic SAR to remove the linear RCM in [28,29,30], but these methods neglect the residual higher-order RCM, which degrades the azimuth focusing performance Another problem is the 2-D variation of Doppler coefficients. In Qiu et al [34], an azimuth NLCS algorithm based on numerical fitting is proposed to process bistatic SAR data with a stationary transmitter This algorithm can only deal with the spatial variance of Doppler frequency modulation rate. The proposed algorithm resolves the problem of the variation of linear RCM and Doppler centroid, and has a better imaging performance for multiple targets in the scene This method is computationally efficient compared to time-domain methods such as back projection (BP) and achieves better focusing performance than other frequency domain methods.
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