Analytical Steady State Solution for a Kalman Tracking Filter

Analytical expressions are given for the steady state solution to a Kalman tracking filter used in a track-while-scan radar system. The radar sensor measures range and range rate, and both these measurements are utilized in the filter. The solution for range measurements only is obtained as a special case. Graphs are also given which show how the solution depends on different parameters.     

A three-state Kalman tracker using position and rate measurements

A three-state Kalman tracker is described for tracking a moving target, such as an aircraft, making use of the position and rate measurements obtained by a track-white-scan radar sensor which employs pulsed Doppler processing, such as the moving target detector providing unambiguous Doppler data. The steady-state filter parameters have been analytically obtained under the assumption of white noise maneuver capability. The numerical computations of these parameters are in excellent agreement with those obtained from the recursive Kalman filter matrix equations. The solution for the case when only the range measurements are available is obtained as a special case of this model. Graphs of normalized covariances and gains are presented to illustrate how the solution depends on different parameters     

压电陶瓷短圆柱耦合振动的研究

 压电陶瓷圆柱振子的振动问题,由于厚向振动和径向振动之间的耦合作用,使问题变得非常复杂。迄今为止,许多研究者在这方面所做的工作,大体上可分为两类:一类是从各向同性圆柱体振动的近似解出发,求解压电陶瓷圆柱振子的振动问题;另一类是从压电陶瓷圆柱振子的压电本构方程组和运动方程组出发,利用数学上的伴随算子法计算其数值解。这两种方法不仅运算过程都相当复杂,而且都不能直观地反映出压电振子的物理参数的影响。     

热空腔-喷气流的组合辐射

讨论了热空腔(喷气发动机的加力筒)和喷气流的组合辐射问题, 推演了组合辐射的辐射传输微分方程, 导出了有边界辐射条件下的解。讨论了由多个温度不同的壁面组成且腔内充满高温燃气的热空腔辐射传输方程解的具体形式, 导出了它向后半球的光谱辐射强度的表达式;同时还推导了热空腔-喷气流组合辐射的光谱辐射强度的表达式。最后给出算例, 算例结果表明, 热空腔-喷气流组合辐射的空间分布具有与实测分布较一致的梨形包络, 其光谱分布也与实测的光谱分布的一致性较好。      

Geolocation of a known altitude object from TDOA and FDOA measurements

Most satellite systems for locating an object on Earth use only time difference of arrival (TDOA) measurements. When there are relative motions between an emitter and receivers, frequency difference of arrival (FDOA) measurements can be used as well. Often, the altitude of an object is known (it is zero, for example) or can be measured with an altimeter. Two sets of geolocation solutions are proposed which exploit the altitude constraint to improve the localization accuracy. One is for TDOAs alone and the other for the combination of TDOA and FDOA measurements. The additional complexity by imposing the constraint is a one-dimensional Newton's search and the rooting of a polynomial. The covariance matrices of the new estimators are derived under a small measurement noise assumption and shown to attain the constrained Cramer-Rao lower bound (CRLB). When there is a bias error in the assumed altitude, using the altitude constraint will introduce a bias to the solution. Since applying the constraint decreases the variance, there is a tradeoff between variance and bias in the mean square error (MSE). The maximum allowable altitude error such that the constraint solution will remain superior to the unconstraint is given. Simulation results are included to corroborate the theoretical development.     

Algebraic two-satellite TOA/FOA position solution on an ellipsoidal Earth

A direct algebraic solution is given for estimates of the ambiguous locations of an RF emitter on the surface of an ellipsoidal Earth given time-of-arrival (TOA) and frequency-of-arrival (FOA) measurements at two satellites.     

计及边界层汇流效应的多段翼型失速特性计算

 本文给出计及边界层汇流效应的多段翼型失速特性的解法。用高阶奇点分布面元法（Panel Method）求位流解,然后进行各翼段粘性尾迹形状迭代,并解出正常边界层和汇流边界层特性。当翼段上有后缘分离时,还要确定分离尾迹的形状,用位移厚度当量源（汇）模拟粘性效应。进行粘/位流迭代直至收敛。上述方法在超过多段翼型失速迎角时仍然有效。计算结果与实验数据比较,符合良好。     

Simple Tracking Filters: Closed-Form Solutions

A closed-form steady-state solution is presented for a three-state tracking filter with continuous position measurements and exponentially correlated target acceleration. Some other related closed-form solutions are discussed, and some comparative performance data is presented for the discrete measurement case.     

PDAF with multiple clutter regions and target models

This paper presents the theory of a new multiple model probabilistic data association filter (PDAF). The analysis is generalized for the case of multiple nonuniform clutter regions within the measurement data that updates each model of the filter. To reduce the possibility of clutter measurements forming established tracks, the solution includes a model for a visible target. That is, a target that gives sensor measurements that satisfy one of the target models. Other features included in the algorithm are the selection of a fixed number of nearest measurements and the addition of signal amplitude to the target state vector. The nonuniform clutter model developed here is applicable to tracking signal amplitude. Performance of this algorithm is illustrated using experimentally recorded over-the-horizon radar (OTHR) data.     

Tracking of Spawning Targets with Multiple Finite Resolution Sensors

In this paper the problem of tracking multiple spawning targets with multiple finite-resolution sensors is considered and a new algorithm for measurement-to-track association with possibly unresolved measurements is presented. The goal is to initialize new tracks of spawned targets before they are resolved from the mother platform so that one has the ability to carry out early discrimination when they become resolved. The multiple scan data association problem is first formulated as a multidimensional assignment problem with explicit new constraints for the unresolved measurements. Then the top M hypotheses tracking (TMHT) is presented where the state estimates and their covariances are modified based on the M best hypotheses through the assignment solutions. A modification to the assignment problem is developed that leads to a linear programming (LP) where the optimal solution can be a noninteger in [0,1]. The fractional optimal solution is interpreted as (pseudo) probabilities over the N - 1 frame sliding window. The best hard (binary) decision assignment solution and the M best via TMHT are compared with the soft decision solution for 2-D tracking scenarios with various sensor configurations. Based on the simulation results, the soft assignment approach has better track maintenance capability than the single best hard assignment and a performance nearly as good as the TMHT. Its computational load is slightly higher than the single best hard assignment but much lighter than TMHT.     

On Optimal Control of Linear Systems in the Presence of Multiplicative Noise

This correspondence considers the problem of optimal regulator design for discrete time linear systems subjected to white state-dependent and control-dependent noise in addition to additive white noise in the input and the observations. A pseudo-deterministic problem is first defined in which multiplicative and additive input disturbances are present, but noise-free measurements of the complete state vector are available. This problem is solved via discrete dynamic programing. Next is formulated the problem in which the number of measurements is less than that of the state variables and the measurements are contaminated with state-dependent noise. The inseparability of control and estimation is brought into focus, and an "enforced separation" solution is obtained via heuristic reasoning in which the control gains are shown to be the same as those in the pseudo-deterministic problem. An optimal linear state estimator is given in order to implement the controller.     

Rendezvous Navigation and Guidance Using a Hand-Held Self-Powered Digital Computer

This paper describes a simplified solution of the space rendezvous problem based on optical sightings taken with a hand-held sextant entered into and processed by a small digital computer. Compared to the manual method described in [1], this approach greatly reduces the astronaut's work load. Also, the computer can provide a more accurate solution, can present more flight plan options (allowing more tradeoffs between fuel usage and time), and can allow greater freedom in the sequencing of measurements and maneuvers. Physical characteristics, input-output parameters, and logic design of the computer are briefly described.     

发动机故障方程的最少故障整体优化解

 发动机故障诊断是根据有限的发动机性能参数的测量值在众多的可能发生但不一定发生的故障之中确定出故障的类别和程度。测量参数与故障参数之间的关系通常表示为亚定的线性方程组△y=A△x,式中△y为测量参数向量而△x为故障参数向量。引入最少故障原理可以对亚定的故障方程组求解。求解方法可分为整体优化解法和组合优化解法两大类。本文给出两种基于最少故障原理的约束整体优化解法。最少故障原理和约束条件的引入可以有效地保证最优解的确定性和合理性。文中还给出了利用整体优化解法进行发动机故障诊断的实例。     

Instantaneous GPS attitude determination

A procedure for instantaneous GPS (Global Positioning Satellite) attitude determination, i.e., a solution for the GPS integrated carrier Doppler wavelength ambiguities using only measurements at a single epoch, is described. Most previous techniques to solve the phase ambiguity problem have required some form of time history processing relying on GPS satellite and/or user motion to provide enough geometry change to eliminate false solutions. The algorithm described assumes three noncollinear antennas and integrated carrier Doppler measurements from four or more satellites. Double-difference processing provides at least three independent observables for the two antenna separation vectors to compute the three attitude Euler angles     

Exact analytical solutions of a nonlinear nonstationary inverse problem of heat conduction for a body with low heat conduction coefficient

The analytical solution of a nonlinear nonstationary inverse problem of heat conduction for a bodies with low heat conduction coefficients of one-dimensional geometry is presented. The solutions obtained make it possible to restore the boundary conditions rather exactly using the results of heat flux measurements.     

溶剂对RTM石英／酚醛复合材料溶液浸润过程影响研究

研究了不同溶剂对于RTM石英/酚醛复合材料溶液浸润过程的影响.采用X光电子能谱(XPS)和原位电子顺磁共振(EPR)研究了石英纤维表面硅烷偶联剂和不同酚醛树脂溶液组分间的界面化学反应.采用TGA和层间剪切强度(ILSS)测试方法研究了溶剂对酚醛树脂分布和材料界面结合强度的影响.结果表明,溶剂能够与酚醛树脂在石英纤维表面形成竞争性吸附,从而影响树脂在RTM模具内部不同位置的分布和复合材料的力学性能.随着溶剂形成氢键能力的增强,其影响程度依次为四氢呋喃＜丙酮＜乙醇.     

Tracker and signal processing for the benchmark problem with unresolved targets

Radar signal processing is particularly important in tracking closely spaced targets and targets in the presence of sea-surface-induced multipath. Closely spaced targets can produce unresolved measurements when they occupy the same range cell of the radar. These issues are the salient features of the benchmark problem for tracking unresolved targets combined with radar management, for which this paper presents the only complete solution to date. In this paper a modified version of a recently developed maximum likelihood (ML) angle estimator, which can produce two measurements from a single (unresolved) detection, is presented. A modified generalized likelihood ratio test (GLRT) is also described to detect the presence of two unresolved targets. Sea-surface-induced multipath can produce a severe bias in the elevation angle measurement when the conventional monopulse ratio angle extractor method is used. A modified version of a recently developed ML angle extractor, which produces nearly unbiased elevation angle measurements and significantly improves the track accuracy, is presented. Efficient radar resource allocation algorithms for two closely spaced targets and targets flying close to the sea surface are also presented. Finally, the IMMPDAF (interacting multiple model estimator with probabilistic data association filter modules) is used to track these targets. It is found that a two-model IMMPDAF performs better than the three-model version used in the previous benchmark. Also, the IMMPDAF with a coordinated turn model works better than the one using a Wiener process acceleration model. The signal processing and tracking algorithms presented here, operating in a feedback manner, form a comprehensive solution to the most realistic tracking and radar management problem to date.     

Joint sensor registration and track-to-track fusion for distributed trackers

Sensor registration deals with the correction of registration errors and is an inherent problem in all multisensor tracking systems. Traditionally, it is viewed as a least squares or a maximum likelihood problem independent of the fusion problem. We formulate it as a Bayesian estimation problem where sensor registration and track-to-track fusion are treated as joint problems and provide solutions in cases 1) when sensor outputs (i.e., raw data) are available, and 2) when tracker outputs (i.e., tracks) are available. The solution to the latter problem is of particular significance in practical systems as band limited communication links render the transmission of raw data impractical and most of the practical fusion systems have to depend on tracker outputs rather than sensor outputs for fusion. We then show that, under linear Gaussian assumptions, the Bayesian approach leads to a registration solution based on equivalent measurements generated by geographically separated radar trackers. In addition, we show that equivalent measurements are a very effective way of handling sensor registration problem in clutter. Simulation results show that the proposed algorithm adequately estimates the biases, and the resulting central-level trucks are free of registration errors.     

压铸镁合金腐蚀疲劳性能的研究

研究了压铸镁合金AM50HP和AZ91HP在大气和模拟海水(3.5% NaCl溶液)环境中的疲劳行为.结果表明:压铸镁合金疲劳裂纹萌生于试样表面或近表面的铸造缺陷处;压铸镁合金AM50HP和AZ91HP在大气环境中具有疲劳极限,其值分别约为100MPa和90MPa,而在模拟海水环境中该两种压铸镁合金均不存在疲劳极限;模拟海水严重恶化压铸镁合金AM50HP和AZ91HP的疲劳性能,并且随着施加载荷的降低,影响加剧;特别地,研究发现模拟海水对压铸AM50HP疲劳性能的恶化程度较压铸镁合金AZ91HP更为严重,且这种影响趋势与该两种镁合金的机械化学性能相一致.