In recent years, ground moving target imaging in synthetic aperture radar (SAR) has attracted the attention of many researchers all over the world. A novel approach is proposed for the ground moving target imaging and motion parameter estimation using single channel SAR. First, a second-order generalised keystone formatting method is used to compensate for the range curvature. Secondly, the estimated slope of the target echo's envelope is used for the range walk compensation. Thirdly, Doppler parameters of moving targets obtained via spectral analysis are used for the imaging and positioning of ground moving targets. Finally, motion parameters of moving targets can be estimated on the basis of the relationship between Doppler and motion parameters. Both numerical and experimental results are provided to demonstrate the performance of the proposed approach.

Approach for single channel SAR ground moving target imaging and motion parameter estimation

This letter proposes a novel parameter estimation method based on keystone transform (KT) and Radon-Fourier transform (RFT) for space moving targets with high-speed maneuvering performance. In this method, second-order KT is used to correct the range curvature and part of the range walk for all targets simultaneously. Then, fractional Fourier transform is employed to estimate the targets' radial acceleration, followed by the quadric phase term compensation. Finally, RFT and Clean technique are carried out to correct the residual range walk, and the initial range and radial velocity of moving targets are further obtained. The advantage of the proposed method is that it can overcome the limitation of Doppler frequency ambiguity and correct range curvature for all targets in one processing step, which simplifies the operation procedure. Simulation results are presented to demonstrate the validity of the proposed method.

A Novel Method for Parameter Estimation of Space Moving Targets

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.

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

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

We propose here a new approach for synthetic aperture radar (SAR) imaging of ground moving targets. The unique characteristic of this approach is that range curvature (i.e., quadratic range migration) can be corrected by a simple processing step. A keystone transform is used to correct range walk (i.e., linear range migration) for all targets without knowing their velocities, and the range curvature is corrected in the range-Doppler domain. The advantage of this approach is that it is simple to implement and can correct range curvature for all targets in one processing step, so that it is computationally efficient. Simulation and experimental SAR data processing results are presented to demonstrate the validity of the proposed approach.

New Approach for SAR Imaging of Ground Moving Targets Based on a Keystone Transform

Imaging of moving targets using synthetic aperture radar (SAR) is a challenging task. Target motion in the range direction causes a cross-range shift of the target in the reconstructed image. Target motion in the cross-range direction causes blurring in the reconstructed image. In prevoius years, a number of researchers have applied time-frequency (T-F) techniques, based on the Wigner-Ville distribution, to SAR imaging of moving targets. Specifically, a series of Wigner-Ville or other T-F transforms is substituted for the series of cross-range FFTs in the customary SAR image formation algorithm. The result is a series of SAR images (instead of just one image), indexed as a function of cross-range, in which the blurring of the target due to cross-range motion is largely eliminated. The cross-range shift due to range motion remains, but can be estimated. We analyze the T-F approach by deriving an approximate closed-form expression for the point-target response of the SAR imaging system, assuming a point target moving with constant velocity and T-F processing using the Wigner-Ville distribution. We then use the point-target response to assess the blur reduction and resolving capabilities of the T-F approach. Simulation results for point targets are presented to validate the derived expression.

D.C. Munson

Papers

An analysis of time-frequency methods in SAR imaging of moving targets