Wenzhen Wu

IAA-Based High-Resolution ISAR Imaging With Small Rotational Angle

The Fourier transform-based range Doppler method is commonly used in an inverse synthetic aperture radar. Although it has achieved good success in most scenarios, its performance is determined by the rotational angle, and the cross-range resolution is extremely low in the case of a small rotational angle. In this letter, to improve the cross-range resolution, a novel cross-range compression scheme based on the iterative adaptive approach (IAA) is proposed. In addition to the standard IAA to achieve high resolution, the efficient IAA is introduced to suppress the sidelobes due to noise. Both the simulation and experimental results demonstrate that the proposed method has the advantages of parameter-free, high accuracy, and high efficiency.

Adaptive ISAR Imaging of Maneuvering Targets Based on a Modified Fourier Transform

Focusing on the inverse synthetic aperture radar (ISAR) imaging of maneuvering targets, this paper presents a new imaging method which works well when the target’s maneuvering is not too severe. After translational motion compensation, we describe the equivalent rotation of maneuvering targets by two variables—the relative chirp rate of the linear frequency modulated (LFM) signal and the Doppler focus shift. The first variable indicates the target’s motion status, and the second one represents the possible residual error of the translational motion compensation. With them, a modified Fourier transform matrix is constructed and then used for cross-range compression. Consequently, the imaging of maneuvering is converted into a two-dimensional parameter optimization problem in which a stable and clear ISAR image is guaranteed. A gradient descent optimization scheme is employed to obtain the accurate relative chirp rate and Doppler focus shift. Moreover, we designed an efficient and robust initialization process for the gradient descent method, thus, the well-focused ISAR images of maneuvering targets can be achieved adaptively. Human intervention is not needed, and it is quite convenient for practical ISAR imaging systems. Compared to precedent imaging methods, the new method achieves better imaging quality under reasonable computational cost. Simulation results are provided to validate the effectiveness and advantages of the proposed method.

Inverse Synthetic Aperture Radar Imaging of Targets with Complex Motion based on Optimized Non-Uniform Rotation Transform

Focusing on the inverse synthetic aperture radar (ISAR) imaging of targets with complex motion, this paper proposes a modified version of the Fourier transform, called non-uniform rotation transform, to achieve cross-range compression. After translational motion compensation, the target’s complex motion is converted into non-uniform rotation. We define two variables—relative angular acceleration (RAA) and relative angular jerk (RAJ)—to describe the rotational nonuniformity. With the estimated RAA and RAJ, rotational nonuniformity compensation is carried out in the non-uniform rotation transform matrix, after which, a focused ISAR image can be obtained. Moreover, considering the possible deviation of RAA and RAJ, we design an optimization scheme to obtain the optimal RAA and RAJ according to the optimal quality of the ISAR image. Consequently, the ISAR imaging of targets with complex motion is converted into a parameter optimization problem in which a stable and clear ISAR image is guaranteed. Compared to precedent imaging methods, the new method achieves better imaging results with a reasonable computational cost. Experimental results verify the effectiveness and advantages of the proposed algorithm.

Deviation analysis of pulse compression in ISAR imaging based on direct intermediate frequency sampling data

Deviation in ISAR images is inevitable, especially for the phase part. Pulse compression is the key process in ISAR Imaging, which is also the source of deviation. Focusing on direct intermediate frequency sampling data obtained from LFM (linear frequency modulation) signal, this paper carefully analyzes the process of matched filtering, the source of deviation in HRRP (high resolution range profile), and proposed several compensation methods in alleviating deviation caused by high speed movement and discrete sampling. Simulation results prove the rationality of deviation analysis and the validity of compensation methods.

Simulation of space-based observed star map in space radiation environment

Due to the speciality of space environment for the observation system, the observed images are interfered by space radiation noise to some extent. To improve the reality of image simulation, we propose a new method of star map simulation with space radiation effect in this paper. First of all, basic star map simulation is realized in this paper. Both star position and lightning magnitude are calculated and modeled. And point diffusion is considered. Then, with the CCD imaging theory, space radiation effects on star map are calculated and modeled. The result indicates that this method can effectually simulate the space-based observed star map in radiation environment.