Signal Sequence Detection Given Noisy, Common Background Image Sets

The optimum processing (likelihood functional) is found for a set of M images {Zm = Sm + Y + Nm}, each the sum of a member Sm of a signal sequence {Sm}, due to an object to be detected and its parameters estimated, a sample function Nm of a noise field {Nm}, and a sample function Y of a common background field {Y}. The noise fields {{Nm}} are independent, zero mean, white Gaussian fields, all independent of the background field {Y}; the latter is assumed to be either 1} completely unknown or of known mean and covariance functions with 2) a certain fluctuation property or 3) Gaussian. Three equivalent forms of the optimum processing are found: 1) a summation of generalized matched filterings of the images, 2) a summation of matched filtering of certain generalized differences of the images, 3) a summation of ?estimator-correlator? type filterings. The detection performance and optimum signal/image selection under the Neyman-Pearson criterion is given and the singularity of the ({{Nm = O}} and M > 1) case noted. It is shown that optimum processor and signal design can completely eliminate any effect of the background on detectability (M > 1). The Cramer-Rao lower bound for the signal parameter estimates meansquare error is given along with an example; optimum signal/image selection in the single parameter case is discussed.     

On the Effective Single Trial Probability of Success

Define the cumulative probability Pn of occurence of some event as the probability that it occurs at least once in n trials. If the single trial probabilities are not fixed, but are drawn from a distribution of their own, or are dependent on some other nonfixed variable, then it would be convenient to have an ?effective single trial probability (esp)? for use in the simple Bernoulli model which would give the same cumulative probability of occurence as actually observed. We show here that the esp can be interpreted as a kind of average, and that its value is given by 1 minus the geometric mean of 1-d(p), where d(p) is the probability density function of the single trial probabilities, the p's. We further define this geometric mean for both discrete and continuous distributions and evaluate the esp for several cases. These results are compared with earlier ones which suggest that the esp is given by the (arithmetic) average or expectation of the single trial probabilities, and we determine under what conditions this simpler result can be used.     

Gyro Motion Boundedness under Uncertain Vehicle Spin and Acceleration

An analysis is presented of the motion of a single axis rate gyroscope mounted in a space vehicle, which is simultaneously accelerating and spinning about the output and spin axis, respectively, of the gyro. The time-varying acceleration and deceleration ?x(t) and the spin rate ?z(t) of the vehicle are unknown but bounded functions of time t. It is shown that the motion of the gyro remains bounded if the bound ?*2 on the uncertainty in ?z(t) does not exceed some threshold ?*2 and that this threshold depends on the various parameters of the gyro. Furthermore, by a proper selection of the gyro parameters, its motion can be forced to remain in a small neighborhood (called region of ultimate boundedness) of the origin in ?-? plane after a certain finite interval of time for any bounded uncertain ?x(t) and ?z(t). Analytical relations are derived for the selection of gyro parameters to keep the error caused in the measurement of the input rate due to ?x and ?z within any given limit.     

相关系数ARMA(p,q)序列分析方法

本文提出相关系数ARMA(p,q)序列分析方法。相关系数ARMA(p,q)序列是从非平稳序列中分离出的一类工程上常见且便于研究的时间序列,在模式识别、故障诊断、信号处理、自动控制和结构响应分析等领域有着广泛的应用。传统的相关函数ARMA(p,q)序列仅是它的一个特例。文中建立了相关系数ARMA(p,q)序列的条件极大似然估计和精确极大似然估计,前者在样本较大时简单便于工程应用,后者则在样本较小时仍具有较高的精度,它们通过时域的全程分析,充分利用样本信息确定相关系数ARMA(p,q)序列的均值函数、方差函数和相关系数函数。在此基础上可进行高精度的频谱分析。     

基于模态滤波器的柔性智能桁架结构振动主动控制实验研究

基于模态滤波器技术和最优控制理论 ,在测量加速度的情况下 ,采用独立模态空间控制方法研究了空间柔性智能桁架结构的振动主动控制问题。在研制了智能桁架结构的基础上 ,基于计算机控制系统理论 ,采用加速度测量进行了柔性智能桁架结构的实时计算机振动主动控制实验研究。实验结果表明该控制方法是行之有效的     

Performance of a Mean Level Detector Processing M-Correlated Sweeps

The performance of a mean level detector processing M-correlated consecutive sweeps is derived. Performance when sweeps are independent can be obtained simply as a special case. The background noise is assumed stationary Gaussian and pulses are fluctuating according to the Swerling I model. Results are obtained for both finite and infinite reference noise samples. It is shown that for fixed M the relative improvement over the single hit case increases when the correlation between sweeps decreases and as the probability of false alarm is kept at lower rates.     

单侧容限对应实际存活率的预测

 研究了单侧容限系数法中子样容量ｎ、置信度γ及名义存活率Ｐ与实际存活率α之间的定量关系,导出了α的预测公式。计算结果表明：在ｎ较小,γ与Ｐ搭配不当时,将出现α小于Ｐ的不合理情况。此时,名义存活率Ｐ将过高地表示了安全性,从而使人盲目乐观。本文指出：在飞机或直升机结构可靠性分析中,子样容量ｎ通常远小于４３,因此,某些文献中建议取γ＝９０％,Ｐ＝０．９９９９９９是不合理的,本文提出了新的建议。     

用联合样本法确定直升机零件的疲劳分散性

在直升机型号的疲劳合格鉴定中,由于经费和时间的限制,同一种零部件的试件数通常不超过6个。由这些试验结果构成的样本在统计学上叫小样本。一般认为,由这种小样本确定的平均值还比较准确,但确定的标准差可能偏离真值甚远。本文介绍一种把小样本试验数据联合起来构成大样本,比较精确地确定标准差的方法。     

Detection by incoherent recombination with partial information

Matched filter (MF) detection in spread environments is often seriously degraded by the mismatch between the waveform replica and the composite signal formed by the spreading environment. Typically the spreading is caused by multiple delayed reflections due to scatter extent or multipath especially in shallow water sonar applications. It is possible to recover some detector performance by incoherent summation of weighted MF realizations in a process called incoherent recombining (IR). Several IR strategies for Gaussian data that assume varying amounts of prior scattering function (SF) information are examined, their receiver operating characteristics (ROCs) computed, and compared with those of the unrealizable “prescient” receiver (PR). They include optimally weighted and unweighted versions of the maximum likelihood estimator-correlator (EC), and variations of the “at-least-one” (ALO) detector that examines sequences of MF realizations declaring a detection if at least one threshold is crossed. As might be expected, performance improves with the accuracy of the prior information incorporated in the detector formulation     

麦道某型飞机系统装配分析

从民用飞机的安全性出发，在分析麦道某型飞机液压系统及操纵系统的特点的基础上，研究其使用的特殊连接件及其加工手段。通过对这些连接件的研究，不仅使我们掌握了其加工方法，提高了飞机的安全性能，也为我们提供研究更多新工艺创造了条件；在保证产品质量的同时，为我们今后在飞机设计及制造中提供了很好的借鉴。     

Linear FM Signal Formats for Beacon and Communication Systems

This paper examines the capabilities of the class of linear FM spread-spectrum signals within the context of potential communications systems usage in order to establish some performance criteria and bounds that permit comparison with other spread-spectrum formats. A systematic basis is provided for parameter selection for this class of signals by examining the interaction a mong the frequency-modulation indices, time-bandwidth product, and cross-talk criteria that determine the number of effective linear FM signals (or channels) that can be used within the constraints of a bounded time-frequency region. A general expression is derived relating N, the number of useful signals, R2, a cross-talk parameter, ToWo, the mean time-bandwidth product, and ?max and ?min, the maximum and minimum FM rates of the signal set. Canonic signal processor structures are described for ensembles of linear FM signals that have either constant duration or constant bandwidth. It is then shown that the signal modulation format can be modified in accordance with classical paired-echo theory to expand the utility of this class of signals in both synchronous and nonsynchronous operations to yield the equivalent of time-division and code multiplexing. Possible applications for this signal format are discussed.     

基于样本熵的语音信号检测算法

船舶自身发出的巨大噪声,严重影响了通讯设备通讯端船舶工作者的正常语音交流和通讯,须要进行语音信号增强,将语音信号从背景噪声中检测分离出来。为此,文章在分析语音信号与船舶背景噪声信号时域序列复杂性基础上,提出基于信号序列样本熵的语音信号检测算法。该算法将含噪信号进行分帧后,首先计算每帧信号的样本熵,并根据自适应预设阈值对信号进行初始判断；然后,利用信号通常持续一定时间的连续性,对信号初始判断进行平滑,得到信号的最终判别类别,实现对语音信号的检测。经过大量实测实验数据的验证,环境噪声信号的辨别准确度为 90.33%,语音信号为 95.05%,该算法取得了较好的判别精度。     

Frequency-Agile Radar Signal Processing

Modern radars may incorporate pulse-to-pulse carrier frequency modulation to increase probability of detection, to reduce Vulnerability to jamming, and to reduce probability of interception. However, if coherent processing is used for clutter rejection, the frequency of N consecutive pulses must be held constant for N-pulse clutter cancellation or Doppler filtering. If M pulses are transmitted during the time the antenna illuminates a target, there are M/N coherently integrated echoes available for noncoherent integration in the computer or the operator's display to further improve the signal-to-noise ratio (SNR). In this paper, analytical and simulation methods are employed to determine the balance between coherent and noncoherent integration that yields the greatest SNR improvement. Attention is focused upon a model using peak selection of fast Fourier transform (FFT) Doppler channels and is compared to a reference model involving only a single Doppler channel. Curves of detectable SNR as a function of M and N are presented for both models.     

An analysis of modern versus classical homing guidance

Three terminal guidance laws incorporated in a generic interceptor are compared: first- and second-order modern guidance laws (MGLs), that are matched to the second-order autopilot of the interceptor, and proportional navigation (PN). The sensitivity of miss distance (MD) between the interceptor and a target to autopilot time constant, damping ratio, and update rate is shown. For the chosen interceptor-target scenario, the second-order MGL achieves significantly improved MD over the other two guidance laws     

多区聚焦技术在粉末高温合金微缺陷检测中的应用

针对大厚度粉末高温合金材料中微缺陷的检测难题,采用多区聚焦检测技术,对粉末高温合金微缺陷试样进行了检测灵敏度、信噪比和C扫描成像试验,并与普通单一探头聚焦检测结果进行比较.试验结果表明,多区聚焦技术检测灵敏度高,信噪比好,对于厚度75mm粉末高温合金材料中的微缺陷具有较好的检测效果.     

基于POD-BPNN的热启动策略及其在气动代理优化中的应用

传统气动优化设计需要大量CFD 分析,而代理优化（SBO）方法能够有效降低CFD 分析次数,但该方法并没有改变单个CFD 分析时间。提出一种基于本征正交分解-反向传播神经网络（POD-BPNN）模型的热启动策略,并应用于气动代理优化。使用POD-BPNN 模型对SBO 中的初始样本建立从几何设计变量到流场数据的预测模型...     

Computation of binary integration detection probabilities

Efficient algorithms are described for computing the probability of detection for a binary integration when the probability of a threshold crossing changes from sample to sample. A binary integrator is exceeded (a hit occurs) in a sequence of N trials and declares a detection if the number of hits is at least as large as some number M, where O>     

Energy Spectra, Composition, and Other Properties of Ground-Level Events During Solar Cycle 23

We report spacecraft measurements of the energy spectra of solar protons and other solar energetic particle properties during the 16 Ground Level Events (GLEs) of Solar Cycle 23. The measurements were made by eight instruments on the ACE, GOES, SAMPEX, and STEREO spacecraft and extend from ～0.1 to ～500–700?MeV. All of the proton spectra exhibit spectral breaks at energies ranging from ～2 to ～46?MeV and all are well fit by a double power-law shape. A comparison of GLE events with a larger sample of other solar energetic particle (SEP) events shows that the typical spectral indices are harder in GLE events, with a mean slope of ?3.18 at >40?MeV/nuc. In the energy range 45 to 80?MeV/nucleon about ～50?% of GLE events have properties in common with impulsive ³He-rich SEP events, including enrichments in Ne/O, Fe/O, ²²Ne/²⁰Ne, and elevated mean charge states of Fe. These ³He-rich events contribute to the seed population accelerated by CME-driven shocks. An analysis is presented of whether highly-ionized Fe ions observed in five events could be due to electron stripping during shock acceleration in the low corona. Making use of stripping calculations by others and a coronal density model, we can account for events with mean Fe charge states of 〈Q _Fe〉≈+20 if the acceleration starts at ～1.24–1.6 solar radii, consistent with recent comparisons of CME trajectories and type-II radio bursts. In addition, we suggest that gradual stripping of remnant ions from earlier large SEP events may also contribute a highly-ionized suprathermal seed population. We also discuss how observed SEP spectral slopes relate to the energetics of particle acceleration in GLE and other large SEP events.     

Overlapping Pulse Trains

An event happens the first time several periodic pulse trains all overlap (are all ?on?) simultaneously. Assuming that all pulse trains are randomly located with respect to each other, it is argued that the time required is approximately an exponential random variable. A formula for the mean of this time and the results of some tests by computer simulation are given.     

Overall Detection Probability for Fluctuating and Nonfluctuating Target Models

The power selection of a search radar is best obtained in the framework of the overall detection probability concept. This concept is here applied to fluctuating target models for single- and multiple-scan detection. The approach combines the pulse train statistics over the detection interval to the mean target statistics over the search region and directly relates the overall detection probability POD to a single system parameter ?0, proportional to the transmitted power.