Target rotation parameter estimation for ISAR imaging via frame processing

Frame processing method offers a model-based approach to Inverse Synthetic Aperture Radar (ISAR) imaging. It also provides a way to estimate the rotation rate of a non-cooperative target from radar returns via the frame operator properties. In this paper, the relationship between the best achievable ISAR image and the reconstructed image from radar returns was derived in the framework of Finite Frame Processing theory. We show that image defocusing caused by the use of an incorrect target rotation rate is interpreted under the FP method as a frame operator mismatch problem which causes energy dispersion. The unknown target rotation rate may be computed by optimizing the frame operator via a prominent point. Consequently, a prominent intensity maximization method in FP framework was proposed to estimate the underlying target rotation rate from radar returns. In addition, an image filtering technique was implemented to assist searching for a prominent point in practice. The proposed method is justified via a simulation analysis on the performance of FP imaging versus target rotation rate error. Effectiveness of the proposed method is also confirmed from real ISAR data experiments.     

机载干涉SAR/ISAR对地面慢速目标成像研究

该文研究用机载干涉SAR/ISAR技术对地面慢速目标成像,该技术利用SAR成像的距离和横向距离高分辨率,以及干涉仪的空域对消,实现杂波抑制,提高信杂比。动目标的真实方位由相位比较干涉仪测定。进而用ISAR处理得到慢速目标的高分辨图像。文中详细讨论了机载干涉SAR/ISAR系统框图和工作原理,并导出了该系统中SAR、干涉仪空域对消和测向以及ISAR处理的定量关系式。理论分析和初步计算机仿真证明了这项技术的正确性。     

采用二阶Keystone变换的机动目标ISAR成像算法

针对具有复杂运动的机动目标在相干成像时间内产生的一阶距离徙动和二阶距离徙动的问题,本文提出了基于二阶keystone变换的二维ISAR成像算法。文章首先结合去调频接收机技术,建立并分析了机动目标的回波信号模型,并对回波信号使用二阶keystone变换以去除二阶距离徙动。然后,采用分数阶傅里叶变换（FrFT）估计二阶keystone变换后新生成的二次相位项的调频斜率,并依此补偿该二次相位项。对补偿后的回波信号再次使用二阶keystone变换去除一阶距离徙动。最后,对回波信号使用2D FFT获取机动目标的高分辨2D ISAR图像。数值仿真和实测数据成像结果验证了本算法的有效性。      

空间自旋运动目标的ISAR成像研究

逆合成孔径雷达(ISAR)是空间目标探测的重要途径.文中对空间自旋运动目标的ISAR成像进行讨论.根据目标自旋运动规律,建立和分析了ISAR回波信号模型,重点分析自旋目标的成像机理,研究了自旋对目标ISAR成像的影响.基于ISAR成像的原理,建立了计算目标ISAR投影像的方法.仿真实验验证了ISAR投影像计算方法的有效性和自旋对ISAR成像影响分析的正确性.该投影像算法也适用于空中目标成像的讨论.     

Three-dimensional ISAR imaging of maneuvering targets using threereceivers

The conventional ISAR image is a two-dimensional (2-D) projection of a three-dimensional (3-D) object surface. The image (projection) plane is related to the motion of a target with respect to the line of radar sight (LOS). In general, the image plane and the image scale in the cross range direction can not be determined by the traditional ISAR system with one receiver unless the target motion knowledge is known. In this paper, we propose a new ISAR system with three receivers. Using the three-receiver ISAR system, 3-D images of maneuvering targets can be generated, where the knowledge of the target motion is not required.     

Editorial: Signal processing techniques for ISAR and feature extraction

Inverse synthetic aperture radar (ISAR) is a non-cooperative target recognition technique that has been investigated for target identification by the combat identification (ID) community for the past decade. Recently, ISAR imaging of moving targets has been an area of vigorous research. ISAR imaging is an effective way to acquire high resolution images of targets of interest at long range and as such is an irreplaceable tool in the task of non-cooperative target recognition. Its applications include detection, imaging, and classification of ships and aircraft with airborne, maritime, and land-based radar systems. Being radar-based, this imaging technique can be employed in all weather and day/night conditions.     

ISAR Imaging of Maneuvering Targets Based on the Range Centroid Doppler Technique

A new inverse synthetic aperture radar (ISAR) imaging approach is presented for application in situations where the maneuverability of noncooperative target is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The proposed algorithm is referred to as the range centroid Doppler (RCD) ISAR imaging technique and is based on the stretch Keystone-Wigner transform (SKWT). The SKWT introduces a stretch weight factor containing a range of chirp rate into the autocorrelation function of each cross-range profile and uses a 1-D interpolation of the phase history which we call stretch keystone formatting. The processing simultaneously eliminates the effects of linear frequency migration for all signal components regardless of their unknown chirp rate in time-frequency plane, but not for the noise or for the cross terms. By utilizing this novel technique, clear ISAR imaging can be achieved for maneuvering targets without an exhaustive search procedure for the motion parameters. Performance comparison is carried out to evaluate the improvement of the RCD technique versus other methods such as the conventional range Doppler (RD) technique, the range instantaneous Doppler (RID) technique, and adaptive joint time-frequency (AJTF) technique. Examples provided demonstrate the effectiveness of the RCD technique with both simulated and experimental ISAR data.     

一种改进的ISAR图像方位向定标方法

确定逆合成孔径雷达（ISAR）图像的方位向像素尺寸,即方位向定标,是正确获得目标外形和尺寸等特征信息的前提。ISAR图像的方位向像素取决于雷达波长和目标相对于雷达视线在相干积累时间内的转角,前者是已知的,但后者在对非合作目标成像方式下难以确定。在研究已有定标算法的基础上,提出了一种改进的ISAR图像方位向定标方法,即首先用最大对比度（IC）和质量评估（QE）准则筛选出多个质量最好的包含特显点的距离单元,然后提取这些单元内特显点的回波信号并估计各特显点的调频率,最后由特显点的距离坐标和调频率获取目标的转动角速度,从而实现ISAR图像的方位向定标。仿真和实测数据的处理结果表明,该算法的定标效果明显优于已有算法。     

一类亚像素分辨的包络对齐方法

包络对齐是逆合成孔径雷达(ISAR)运动补偿的基础,现有的包络对齐方法普遍存在对齐精度低和运算时间长的缺点。本文在最大相关法包络粗对齐的基础上,采用最大相关系数,运用二次估值与遍历/搜索算法确定精细偏移量。这些方法具有更高的对齐精度。采用相关系数的快速算法,新方法运算速度相比传统最大相关法差别不大。外场实测数据的处理结果表明这些方法的有效性。     

基于高精度运动信息的ISAR分辨率评估方法

ISAR分辨率评估是空间目标成像雷达精度鉴定的重要内容。该文针对ISAR分辨率评估中的基准计算与方法设计两个关键问题进行了详细分析,进而提出了基于空间目标高精度轨道与遥测姿态等运动信息的ISAR方位向定标方法。在此基础上,建立了一种新的ISAR分辨率评估方法。利用某雷达精度鉴定试验中对不同空间目标的实测成像数据,验证了该文方法的合理性与有效性。     

High-resolution ISAR imaging of maneuvering targets by means of therange instantaneous Doppler technique: modeling and performance analysis

Very high resolution inverse synthetic aperture radar (ISAR) imaging of maneuvering targets is a complicated task. In fact, the conventional range Doppler (RD) ISAR technique does not work properly when target motions generate terms higher than the first order in the phase of the received signal relative to each scatterer. This effect typically happens when at least one of these situations occur: (1) very high resolution images are required; (2) the target maneuvers; and (3) the target undergoes significant angular motions (roll, pitch, and yaw). A novel ISAR technique, named range instantaneous Doppler (RID), has been proposed for the reconstruction of very high resolution images of maneuvering targets. In this paper, we analytically show that the RID technique works properly when high-resolution ISAR images are required of maneuvering and/or rolling, pitching, and yawing targets; we also quantify the performance improvement of the RID technique with respect to the RD technique. The problem is tackled from an analytical point of view. First, we define a new model of the ISAR received signal that is valid for maneuvering targets, then we derive and compare the analytical expression of the point spread function (PSF) for the two techniques. Furthermore, we perform a statistical analysis to evaluate the improvement of the RID technique versus the RD technique in terms of spatial resolution. Finally, we prove the effectiveness of the RID technique by simulating the imaging process for two different targets: (1) a ship that undergoes roll, pitch and yaw motions and (2) a fast maneuvering airplane.     

幅度和相位估计的ISAR超分辨成像方法

传统距离多普勒(Range Doppler, RD)成像方法分辨率取决于发射信号的带宽和信号在方位向积累的多普勒带宽。超分辨成像可以在给定带宽条件下,获得比RD方法更优的分辨率。给出一种基于幅度和相位估计(Amplitude and Phase Estimation, APES)的逆合成孔径雷达(Inverse Synthetic Aperture Radar, ISAR)超分辨成像方法,该方法根据回波数据构造自适应滤波器对目标散射点进行重建,仿真和实测ISAR数据成像结果验证了基于APES的ISAR超分辨成像算法的有效性。相比其他超分辨成像方法,该方法重建的散射点幅度更为精确,副瓣更低,图像对比度和图像信噪比增加,整体成像效果较佳。     

Three-dimensional scattering center extraction using the shootingand bouncing ray technique

We present a technique to extract the three-dimensional (3-D) scattering center model of a complex target. Using the shooting and bouncing ray technique, we first generate the 3-D inverse synthetic aperture radar (ISAR) image of the target based on a one-look ISAR algorithm. In step two, we use the image processing algorithm CLEAN to extract the 3-D position and strength of the scattering centers from the 3-D ISAR image. Various implementation issues related to computation time and memory are addressed and an efficient scheme is presented to accomplish the 3-D scattering center extraction. Several examples ranging from simple canonical structures to complex targets are presented to demonstrate the validity of the extraction scheme and the usefulness of the resulting 3-D scattering center model     

基于二阶WVD的ISAR平动补偿方法

逆合成孔径雷达（Inverse synthetic aperture radar, ISAR）目标成像在军事和民用领域有着很广泛地应用,近年来,ISAR目标成像技术发展已经较为成熟,然而由于观测场景复杂和目标的非合作特性,导致获取的目标图像分辨率低和出现散焦、拖尾等问题。针对上述问题,本文提出了一种基于二阶维格纳维拉分布（Wigner-viller Distribution,WVD）的ISAR平动补偿方法,该方法首先将ISAR回波信号建模为二阶多项式,然后运用Keystone变换校正由运动引起的距离走动,再利用二阶WVD变换聚焦目标所有散射体的能量,进而估计出二阶运动参数,最后通过解调操作和Keystone变换获得聚焦良好的目标图像。本文提出的方法在低信噪比（Signal-to-noise ratio,SNR）环境下具有较稳定的性能,并且避免了多维搜索,减少了运算复杂度,有利于实现ISAR运动目标的实时成像。      

基于相干化处理的步进频率ISAR成像算法研究

在步进频率高分辨ISAR成像中,传统的参数估计方法往往不能准确地估计出运动目标的速度和加速度值,其补偿后存在的相位误差对宽带合成ISAR图像有较大的影响。因此,该文提出了一种基于相邻相关法和相位相干化的步进频率高分辨ISAR成像技术,即通过相邻相关法估计运动目标的径向运动参数,在对回波数据包络进行补偿后,利用相位相干化对各子脉冲的相位误差进行校正,再利用频带拼接技术获取目标的合成高分辨1维距离像。之后,利用RD算法实现目标的高分辨ISAR成像。该方法具有精确相位误差补偿精度和高运算效率的优点。仿真和实测数据验证了该方法的有效性。     

Blind-velocity SAR/ISAR imaging of a moving target in a stationarybackground

A synthetic aperture radio/inverse synthetic aperture radar (SAR/ISAR) coherent system model and inversion to image a target moving with an unknown constant velocity in a stationary background are presented. The approach is based on a recently developed system modelling and inversion principle for SAR/ISAR imaging that utilizes the spatial Fourier decomposition of SAR data in the synthetic aperture domain to convert the SAR system model's nonlinear phase functions into linear phase functions suitable for a computationally manageable inversion. It is shown that SAR/ISAR imaging of a moving target can be converted into imaging the target in a stationary squint-mode SAR problem where the parameters of the squint-mode geometry depend on the target's velocity. A method for estimating the moving target's velocity that utilizes a spatial Doppler analysis of the SAR data within overlapping subapertures is presented. The spatial Doppler technique does not require the radar signal to be narrowband, so the reconstructed image's resolution is not sacrificed to improve the target's velocity estimator.     

空间目标逆合成孔径成像实验研究

逆合成孔径雷达(ISAR),由于其良好的空间分辨能力,非常适合于空间目标的探测研究。它通过采用宽带信号来获得高距离分辨能力,通过对目标不同方向上接收回波进行相干处理来获得精细的横向距离(方位)分辨能力。这种雷达得到的高分辨二维图像提供了更好的目标特征探测性能。文中给出了一种用于空间目标逆合成孔径成像的实验研究。     

Three-dimensional interferometric ISAR imaging for targetscattering diagnosis and modeling

Two-dimensional (2-D) inverse synthetic aperture radar (ISAR) imaging has been widely used in target scattering diagnosis, modeling and target identification. A major shortcoming is that a 2-D ISAR image cannot provide information on the relative altitude of each scattering center on the target. In this paper, we present an interferometric inverse synthetic aperture radar (IF-ISAR) image processing technique for three-dimensional (3-D) target altitude image formation. The 2-D ISAR images are obtained from the signature data acquired as a function of frequency and azimuthal angle. A 3-D IF-ISAR altitude image can then be derived from two 2-D images reconstructed from the measurements by antennas at different altitudes. 3-D altitude image formation examples from both indoor and outdoor test range data are demonstrated on complex radar targets.     

Joint time-frequency ISAR using adaptive processing

A new joint time-frequency inverse synthetic aperture radar (ISAR) algorithm that combines ISAR processing with the joint time-frequency signal representation is presented as a means of extracting the nonpoint-scattering features from the standard ISAR image. The adaptive Gaussian representation, applied to the range aids of the ISAR image, is used as the time-frequency processing engine. This technique uses Gaussian basis functions to adaptively parameterize the data and, as a consequence, the point-scattering mechanisms and resonance phenomena can be readily separated based on the width of the Gaussian bases. The adaptive joint time-frequency ISAR algorithm is tested using data generated by the moment-method simulation of simple structures and the chamber measurement data from a scaled model airplane. The results show that nonpointscattering mechanisms can be completely removed from the original ISAR image, leading to a cleaned image containing only physically meaningful scattering centers. The nonpoint-scattering mechanisms, when displayed in the frequency-aspect plane, can be used to identify target resonances and cutoff phenomena     

基于线特征差分投影的空间目标姿态估计方法

空间目标姿态估计是有效实现基于ISAR图像空间目标识别的重要前提。本文针对利用线特征二维投影进行姿态估计时,线特征投影的检测误差会严重影响姿态估计精度这一问题,提出一种基于线特征差分投影的空间目标姿态估计方法。该法利用DP算法检测线特征在ISAR图像中的投影,通过建立线特征在实测ISAR图像和姿态估计值下的仿真图像中的二维差分投影,将线特征投影检测的绝对误差转化成相对误差,有效减小了线特征投影的检测误差对姿态估计的影响;同时,利用差分投影求取姿态估计的修正量,形成姿态估计的优化迭代过程,不断提高姿态估计精度。仿真实验验证了方法的可靠性与有效性。