Penghui Huang

A Fast SAR Imaging Method for Ground Moving Target Using a Second-Order WVD Transform

In synthetic aperture radar (SAR) imaging of a ground moving target, long-time coherent integration may effectively improve the imaging quality, whereas the imaging performance may severely degrade due to the range migration and the Doppler frequency migration. In this paper, a novel motion parameter estimation method named second-order Wigner-Ville distribution (SoWVD) transform is proposed, and then, a new SAR imaging method based on the SoWVD for a ground moving target is developed. As a modified Wigner-Ville distribution method, the SoWVD method can estimate the motion parameter without the search procedure, which achieves motion parameter estimation by Fourier transform operations in the 2-D frequency plane with respect to the slow time and the delay time. In addition, it can effectively recognize the cross terms based on multiple symmetrical properties of the peaks in the 2-D frequency domain. Both simulated and real data processing results are presented to validate the proposed imaging method.

Long-Time Coherent Integration for Weak Maneuvering Target Detection and High-Order Motion Parameter Estimation Based on Keystone Transform

In the airborne or spaceborne radar applications, prolonging the coherent integration time is one of the effective methods to improve the radar detection ability of a weak maneuvering target, whereas the coherent integration performance may degrade due to the complex range migration (RM) and Doppler frequency migration (DFM) effects. In this paper, detection and motion parameter estimation for a weak maneuvering target with the third-order RM and DFM are considered. Firstly, Keystone transform is applied to compensate the linear range walk. Then, the matched filtering processing is performed in the range-frequency and azimuth-time domain to eliminate the residual coupling effects between range and azimuth. Finally, a well-focused image of a moving target is obtained, and three motion parameters, i.e., velocity, acceleration, and acceleration rate, are effectively estimated. In addition, as for a fast-moving target with Doppler ambiguity, two cases, i.e., target azimuth spectrum within a pulse repetition frequency (PRF) and spanning over neighboring PRF bands, are analyzed. Compared with the generalized Radon Fourier transform (GRFT), the proposed method can acquire a close integration performance but with lower computational complexity since the parameter searching dimension is reduced. Simulated processing results are provided to validate the effectiveness of the proposed method.

An approach for refocusing of ground fast-moving target and high-order motion parameter estimation using Radon-high-order time-chirp rate transform

Long synthetic aperture time can improve the imaging quality of a ground moving target, whereas a moving target may be severely smeared in the cross-range image due to the range migration and the Doppler frequency migration. In this paper, the effects of the third-order Doppler broadening and Doppler ambiguity of a fast-moving target are considered. To address these issues, a novel motion parameter estimation method named high-order time-chirp rate transform (HTRT) is proposed, and then a new synthetic aperture radar (SAR) imaging method based on Radon-HTRT (RHTRT) for a ground moving target is developed. The major contributions are as follows: 1) The proposed SAR imaging method can eliminate the Doppler ambiguity effect. 2) The proposed method can realize longer time coherent integration than Radon-Fourier transform (RFT) and Radon-fractional Fourier transform (RFRFT) methods. 3) The proposed method is computationally efficient since HTRT can obtain the motion parameters of a moving target via performing the 2-dimensional (2-D) fast Fourier transform (FFT). Both the simulated and real data processing results show that the proposed method can finely image a ground moving target in a high signal-to-clutter and noise ratio (SCNR) environment.

Ground Maneuvering Target Imaging and High-Order Motion Parameter Estimation Based on Second-Order Keystone and Generalized Hough-HAF Transform

This paper proposes a new method to focus a ground moving target with complex motions and estimate its motion parameters in a synthetic aperture radar (SAR) system. In this method, the second-order Keystone transform is applied to correct the range curvature. Then, the Hough transform is applied to estimate the slope of the range walk trajectory, from which the target cross-track velocity is obtained. Finally, a generalized Hough-high-order ambiguity function (GHHAF) transform is applied to transform the target signal into a 2-D time-frequency plane and estimate its slope associated with the third-order Doppler parameter. Compared with the conventional SAR imaging methods using the second-order phase model, the proposed method can obtain better imaging quality since the third-order Doppler frequency migration is effectively eliminated. Both simulated and real data processing results are provided to validate the effectiveness of the proposed algorithm.

An Approach for Refocusing of Ground Moving Target Without Target Motion Parameter Estimation

In synthetic aperture radar (SAR), long integration time may induce range migration and Doppler frequency migration of a received signal, which may degrade the SAR imaging performance of ground moving targets. Most of the conventional algorithms deal with the problems of range migration and Doppler frequency migration based on parameter searching. However, the exhaustive searching of target motion parameters may result in heavy computational burden. To avoid this problem, this paper proposes a new imaging method for ground moving targets without target motion parameter estimation. First, Keystone transform is applied to correct the range walk. Second, range curvature is compensated by the matched filtering function. Third, Doppler frequency migration is compensated via multiplying the data in range- and azimuth-time domains by its reversed conjugate data according to the equal interval sampling of the azimuth slow time, which avoids the searching procedure for target motion parameter estimation. Finally, the signal energy will be well accumulated in the range-Doppler domain, and thus, the moving targets can be efficiently recognized in the focused image. The major advantage of the proposed method is that it can obtain well-focused images of all targets in one processing step without target motion parameter estimation; thus, it is computationally efficient. Both simulated and real data processing results are used to validate the effectiveness of the proposed method.

Ground moving target imaging and motion parameter estimation using radon-second-order WVD transform

For a SAR system with a moving target, long synthetic aperture time may greatly improve the SAR imaging quality, whereas defocusing may occur due to the range cell migration (RCM) and Doppler frequency migration (DFM) effects. To address those issues, a key procedure is to perform the accurate motion compensation, and then, the motion parameter estimation becomes essential. In this paper, a novel motion parameter estimation method named Second-order WVD (SoWVD) transform is proposed, which can achieve motion parameter estimation by 2-D Fourier transform (FT) instead of the exhaustive search of the trajectory slope in time-frequency plane by Wigner-Hough transform (WHT). In the sequel, a new SAR imaging method based on a combined Radon-SoWVD transform is developed, which can simultaneously eliminate the RCM and DFM effects without the restriction of Doppler ambiguity. After compensating target motion effect according to the estimated motion parameters, a ground moving target can be finely imaged. Real data processing results are provided to demonstrate the validity of the proposed imaging method.

A fast ground moving target focusing method based on first-order discrete polynomial-phase transform

Abstract A new ground moving target focusing method for airborne synthetic aperture radar (SAR) is introduced in this paper. Firstly, first-order discrete polynomial-phase transform (DPT) is used to reduce the target phase order. Secondly, Keystone transform (KT) is applied to correct the residual range walk, and then the target second-order motion parameter can be estimated after performing the azimuth fast Fourier transform (FFT). Finally, the target first-order motion parameter can be estimated after the Doppler frequency migration (DFM) compensation and a well-focused result of a moving target can be obtained. Compared with the conventional SAR imaging methods, the proposed method can eliminate the effects of Doppler ambiguity and azimuth spectrum split. In addition, the proposed method is computationally efficient since the target motion parameter searching procedure is avoided, which can satisfy the target real-time imaging requirements. Real data processing results are provided to validate the effectiveness of the proposed algorithm.

Ground Moving Target Imaging Based on Keystone Transform and Coherently Integrated CPF With a Single-Channel SAR

It is well known that ground moving targets may be smeared in a synthetic aperture radar (SAR) image due to the range migration, Doppler phase broadening, and velocity ambiguity caused by target unknown motion parameters, especially for the accelerating targets within a long observation time. To deal with these problems, a maneuvering target refocusing method based on keystone transform (KT) and coherently integrated cubic phase function (CICPF) is proposed in this paper. First, an azimuth deramp function is constructed along the slow-time dimension at each range-frequency gate to reduce the order of envelope migration and phase response over the slow-time. Then, the residual range walk and the time-varying Doppler phase are eliminated by the KT and the CICPF, respectively. With the estimated motion parameters, moving targets can be finely refocused. Both simulated and real SAR data processing results are presented to validate the proposed algorithm.

A new method for ground moving target imaging with single-antenna SAR

When the synthetic aperture radar (SAR) imaging is applied to observe a ground scene containing a ground moving target, the moving target image will be typically smeared due to the range cell migration and Doppler spectrum broadening caused by target motions. To eliminate these motion effects, a novel algorithm for ground moving target imaging, which is based on an improved axis rotation-time reversal transform (IAR-TRT), is proposed in this paper. In this method, the linear range migration is corrected by an improved axis rotation (IAR) operation and then the coherent integration is accomplished by a time reversal transform (TRT). The proposed method has low computational complexity since the exhaustive searching for the Doppler chirp rate estimation is avoided, which is suitable for real-time imaging. In addition, the defocusing influence of Doppler ambiguity can be eliminated. The effectiveness of the proposed algorithm is demonstrated by the simulation results in a single-channel airborne SAR system.

A two-step detector based on point spread function feature for multi-channel SAR-GMTI radar

When the energy of a moving targets main-lobe and that of side-lobes are both evidently greater than the average lever of residual clutter plus noise, a moving target may be detected as multiple targets, i.e., the side-lobes may be detected as another targets, which often results in the overload of radar system. However, the side-lobes may not be removed by adopting the conventional detectors exploiting the amplitude or amplitude-phase features for the fact that they have the similar phase feature to the main-lobe. To address this issue, we propose a new two-step detector based on point spread function (PSF) feature for Multi-channel SAR-GMTI Radar to eliminate this kind of repetitive detection for a potential target. The effectiveness of the proposed method is validated by the real dual-channel air-borne synthetic aperture radar (SAR) data for ground moving target indication (GMTl).