Angular Glint and the Moving, Rotating, Complex Radar Target

Angular glint produces errors in radar-indicated target direction and in the Doppler frequency. Glint arises from phase perturbations of the radar signal echoed from a complex target, as compared to those from a point target. The phase gradient V? represents these glint effects very well. The direction of this vector is that of radar angle sensing. The Doppler shift is obtined from the dot product of the gradient and the target velocity. A procedure that isolates and measures glint phase variations alone, for the inaccessible target, is described.     

Requirements for optimal glint reduction by diversity methods

Target “glint” (the difference between the phase-front gradient of the scattered field and the true target direction vector) is related to the analytic properties of the scattered field. The resulting model is used to reinterpret diversity methods for glint reduction and to more accurately specify system requirements. A relationship for estimating the best possible improvement in target bearing estimation is also developed     

Reduction of Radar Tracking Errors with Frequency Agility

Frequency agility with random frequency in each pulse gives an improvement in radar angle tracking with a monopulse radar. With a conical-scan tracking radar, the glint error is reduced but fading error can be increased, and the net result must be studied in each case. A theory, usable for calculating angle tracking errors with a frequency agile radar, is given, and two examples showing the error reduction are presented. According to the theory, one part of the glint or fading spectra is ``smeared out' to half the pulse repetition frequency. Another part, the size of which depends on the degree of correlation between pulses, keeps the form of the original spectrum.     

A nonlinear IMM algorithm for maneuvering target tracking

In target tracking, the measurement noise is usually assumed to be Gaussian. However, the Gaussian modeling of the noise may not be true. Noise can be non-Gaussian. The non-Gaussian noise arising in a radar system is known as glint noise. The distribution of glint noise is long tailed and will seriously affect the tracking performance. We develop a new algorithm that can effectively track a maneuvering target in the glint environment The algorithm incorporates the nonlinear Masreliez filter into the interactive multiple model (IMM) method. Simulations demonstrate the superiority of the new algorithm     

Frequency-Agility Processing to Reduce Radar Glint Pointing Error

A technique to reduce radar pointing errors due to glint using frequency agility and amplitude weighting is presented. The reduction in rms tracking error is developed into an equation dependent upon the original glint tracking error, ?g, and the number of returns weighted, N. The rms tracking error is thereby reduced approximately by a factor of N. Finally, the equation formulated allows one to evaluate the reduction in glint error versus the number of frequencies chosen for frequency agility.     

A Real-Time Statistical Radar Target Model

Radar glint arises from the spatial phase perturbations of the radar signal echoed from a complex target. The glint phenomenon is closely related to the target radar cross section (RCS). This relationship plays a significant part in modern missile seeker signal processing. We present a statistical glint/RCS target model for realtime simulation of target signatures. Particular emphasis is placed upon the modeling and simulation of the appropriate glint/RCS statistical dependency. The fundamental approximation of locating uniformly distributed scatterers around the instantaneous radar centroid employed in the Delano-Gubonin [1, 2, 3] model is removed. A key result which follows from this representation is that the mean glint estimator is unbiased. This enables the estimation of model parameters from the first-order glint and RCS statistics which can easily be computed from measured data. A method of estimating model parameters is presented, and the results are applied to data from a typical combat aircraft target. It is shown that the Delano-Gubonin results are a special case of the results presented here. The 14.6 percent probability of glint falling beyond the target extent as derived by Delano [1] is not true in general. It is further shown that glint and RCS are uncorrelated but are statistically dependent. A Monte-Carlo simulation is performed to verify the assumptions made and to demonstrate the feasibility of the working models.     

基于位置信息的高分辨雷达角闪烁抑制方法

角闪烁误差是导引头寻的制导的主要误差来源,基于高分辨力雷达的单脉冲测角算法可有效改善角闪烁现象。现有的研究大多基于幅度加权的思想,利用距离单元的幅度信息进行加权平滑处理。本文在现有高分辨测角算法的基础上,结合高分辨一维距离像的位置信息,提出了一种新的角度信息处理方法。该算法充分利用了距离像有效单元的目标信息,提高了角度测量精度。仿真实验表明该算法对角闪烁有较好的抑制作用。     

Radar Target Pointing Error Reduction Using Extended Kalman Filtering

A new method of reducing target glint errors in radar systems is presented. The target is modeled as n reflectors whose magnitudes and phases are known. The reflector positions are described by a dynamical model driven by white Gaussian noise. The resulting vibrations of the target reflectors produce glintlike pointing errors in the radar system. An extended Kalman filter is developed to estimate the positions of the target reflectors; this information is used to substantially reduce the pointing error due to glint. Data illustrating this glint reduction is given. The model is extended by the inclusion of clutter effects modeled in the same fashion as the glint phenomenon. The results presented indicate the limits of usefulness of this technique as a function of both receiver noise and relative clutter amplitude.     

A Statistical Glint/Radar Cross Section Target Model

We review the details of the glint (angular scintillation) problem in electromagnetic scattering. These results are employed to develop a statistical glint and radar cross section (RCS) target model featuring the correct glint probability density function, the correct time correlations of RCS and glint, and the correct cross correlation between RCS and glint. This model is suitable for simulation applications, and an implementation scheme for a glint/RCS signal generator is included.     

On analytical evaluation of glint error reduction for frequency-hopping radars

Analytical techniques are presented for evaluating the glint error reduction of frequency-agile tracking radars employing discrete frequency-hopping (FH). The techniques can be used to compare the tracking accuracies obtained with different procedures for frequency selection. The cases of random, cyclic, and hybrid FH are worked out in detail. An illustration using a simple alpha-beta tracking filter indicates that the preferred type of frequency selection usually depends on the filter gains used in a specific application.<>     

Further results on radar pointing error reduction using discreteextended Kalman filtering

A recently proposed method of reducing target glint errors in radar systems using extended Kalman filtering is further extended with the inclusion of and compensation for clutter effects. A discrete target model and discrete Kalman filter (DKF) are used. Simulation results demonstrating the DKF are presented, and the limits on the effectiveness of the method are investigated. The major advantage of the DKF is that it can be implemented in software in the digital processor of the radar, offering flexibility over continuous time filters. The ability of the filter to reduce clutter effects further demonstrates the usefulness of this technique for radar pointing error reduction     

Rapid Determination of Glint Spectral Parameters for Symmetrical Two-Complex-Source Targets

Formulas for glint spectra due to Varshavchik, and based on FM noise theory, are applied to a symmetrical two-complex-source target, such as a twin-jet aircraft. Simple formulas are presented for the glint spectral density at zero frequency and for ?3-dB frequency.     

Maximum likelihood identification of glint noise

If the non-Gaussian distribution function of radar glint noise is known, the Masreliez filter can be applied to improve target tracking performance. We investigate the glint identification problem using the maximum likelihood (ML) method. Two models for the glint distribution are used, a mixture of two Gaussian distributions and a mixture of a Gaussian and a Laplacian distribution. An efficient initial estimate method based on the QQ-plot is also proposed. Simulations show that the ML estimates converge to truths     

导弹制导精度MATRIXx伴随分析系统

回顾了伴随方法在线性时变系统误差分析中的应用。结合MATRIXx的SystemBuild Access（SBA）功能，开发出了能够自动生成原系统的伴随系统的工具软件，并进一步将其应用于制导系统精度分析当中，使其能够在闪烁噪声、多目标以及蛇行目标机动等因素的影响下，对更真实的制导回路的脱靶量进行分析。     

An interacting multiple model approach for target tracking withglint noise

The application of the interacting multiple model (IMM) estimation approach to the problem of target tracking when the measurements are perturbed by glint noise is considered. The IMM is a very effective approach when the system has discrete uncertainties in the dynamic or measurement model as well as continuous uncertainties. It is shown that this method performs better than the “score function” method. It is also shown that the IMM method performs robustly when the exact prior information of the glint noise is not available     

Unification and comparison between two concepts of radar targetangular glint

This paper provides a general proof of unification between two concepts of radar target angular glint. The analysis of a two-point target model, consisting of an electrically and magnetically ideal dipole, shows the relation, difference, and equivalent condition between them more clearly. Angular glint has been synthesized from the measured data of radar echo phase, and compared with the theoretical result     

Data association for deghosting in Y-shaped passive linear array sonars

This paper deals with data association using three sets of passive linear array sonars (PLAS) geometrically positioned in a Y-shaped configuration, fixed in an underwater environment. The data association problem is directly transformed into a 3D assignment, which is known to be NP hard. For generic passive sensors, it can be solved using conventional algorithms, while in PLAS, it becomes a formidable task due to the presence of bearing ambiguity. Thus, the central issue of the problem in PLAS is how to eliminate the bearing ambiguity without increasing tracking error. To solve this problem, the 3D assignment algorithm used the likelihood value of only those observed bearing measurements is modified by incorporating frequency information in consecutive time-aligned scans. The region of possible ghost targets is first established by the geometrical relation of PLAS with respect to target. The ghost targets are then confirmed and eliminated by generating multiple observations in consecutive scans. Representative simulations demonstrate the effectiveness of the proposed approach.     

Feedback median filter for robust preprocessing of glint noise

Glint noise may arise in a target tracking system. The non-Gaussian behavior of glint noise can severely degrade the tracking performance. Measurement preprocessing at the front-end of the tracker is an effective method to reduce glint noise. The preprocessor proposed by Hewer, Martin, and Zeh (1987), which used the computationally intensive M-estimator, may not be suitable for practical implementation. An alternative method employing the median filter is studied here. The median filter is well known for its simplicity and robustness. However, the efficiency of the median filter can be seriously degraded if input samples are not identically distributed. This is what we may encounter in the tracking problem. A feedback median filter is then proposed to overcome this impediment without substantially increasing complexity. Simulations show that the new preprocessor can greatly improve tracking performance in the glint noise environment.     

基于单数码相机自由拍摄的空间点定位

 提出并实现了一种空间点定位方法。该方法仅用一台数码相机围绕目标进行多角度自由拍摄获得多帧图像,采用一套具有身份唯一性的标记点实现多图像间点的稳定匹配;在此基础上根据多视图几何约束,精确计算各次拍摄时的相机姿态和位置;进而求解目标点的三维位置信息,并对结果进行优化。实验表明空间点定位的相对误差优于0.03%。该方法所用设备十分简单,操作方式非常灵活,适用于大型物体多视角测量的拼合、某些情况下的装配检查等,也可直接用于较规则构型物体的三维数据获取与CAD模型重建。     

X射线脉冲星导航硬件脉冲轮廓累积研究

为了在X射线脉冲星地面实验系统仿真源模拟产生X射线的基础上,能够快速稳定地得到脉冲轮廓,采用硬件历元叠加的方法获得脉冲轮廓。研究了用硬件实现历元叠加及其数据整合的算法,该算法首先在MATLAB现场可编程逻辑阵列(FPGA)中实现,再通过MATLAB硬件描述语言(HDL)代码生成模块把算法转换成HDL,经编译后获得配置硬件的Bit文件,最终在开发板FPGA上实现数据处理的硬件模块。一段时间内的光子到达时间数据通过MATLAB算法得到的脉冲轮廓数据与通过硬件模块处理后得到的数据结果存在误差,在单个时间窗口内误差最大值为2个光子数,误差平均值占光子数统计平均值的0.084%;两组统计的脉冲轮廓数据中不同数据占总数据个数的9.481%,这样的误差不影响后端模拟导航模块的导航。利用硬件实现的历元叠加及其数据整合模块具有处理速度快、设备紧凑、功耗低的特点,为航天器利用X射线脉冲星导航提供了一种可行的硬件数据处理技术上的支持。