共查询到20条相似文献,搜索用时 15 毫秒
1.
Bharadwaj P. Runkle P. Carin L. Berrie J.A. Hughes J.A. 《IEEE transactions on aerospace and electronic systems》2001,37(2):595-606
Wideband electromagnetic fields scattered from N distinct target-sensor orientations are employed for classification of airborne targets. Each of the scattered waveforms is parsed via physics-based matching pursuits, yielding N feature vectors. The feature vectors are submitted to a hidden Markov model (HMM), each state of which is characterized by a set of target-sensor orientations over which the associated feature vectors are relatively stationary. The N feature vectors extracted from the multiaspect scattering data implicitly sample N states of the target (some states may be sampled more than once), with the state sequence modeled statistically as a Markov process, resulting in an HMM due to the “hidden” or unknown target orientation. In the work presented here, the state-dependent probability of observing a given feature vector is modeled via physics-motivated linear distributions, in lieu of the traditional Gaussian mixtures applied in classical HMMs. Further, we develop a scheme that yields autonomous definitions for the aspect-dependent HMM states. The paradigm is applied to synthetic scattering data for two simple targets 相似文献
2.
Rago C. Willett P. Bar-Shalom Y. 《IEEE transactions on aerospace and electronic systems》1996,32(2):554-568
We consider a new scheme for distributed detection based on a “censoring” or “send/no-send” idea. The sensors are assumed to “censor” their observations so that each sensor sends to the fusion center only “informative” observations, and leaves those deemed “uninformative” untransmitted. The main result of this work is that with conditionally independent sensor data and under a communication rate constraint, in order to minimize the probability of error, transmission should occur if and only if the local likelihood ratio value observed by the sensor does not fall in a certain single interval. Similar results are derived from Neymarr-Pearson and distance-measure viewpoints. We also discuss simplifications for the most interesting case that the fusion center threshold is high and the communication constraint is severe. We compare censoring with the more common binary-transmission framework and observe its considerable decrease in communication needs. Finally, we explore the use of feedback to achieve optimal performance with very little communication 相似文献
3.
Raghavan R.S. Qiu H.F. McLaughlin D.J. 《IEEE transactions on aerospace and electronic systems》1995,31(2):647-657
We develop a constant false-alarm rate (CFAR) approach for detecting a random N-dimensional complex vector in the presence of clutter or interference modeled as a zero mean complex Gaussian vector whose correlation properties are not known to the receiver. It is assumed that estimates of the correlation properties of the clutter/interference may be obtained independently by processing the received vectors from a set of reference cells. We characterize the detection performance of this algorithm when the signal to be detected is modeled as a zero-mean complex Gaussian random vector with unknown correlation matrix. Results show that for a prescribed false alarm probability and a given signal-to-clutter ratio (to be defined in the text), the detectability of Gaussian random signals depends on the eigenvalues of the matrix Rc-1Rs. The nonsingular matrix Rc and the matrix Rs are the correlation matrices of clutter-plus-noise and signal vectors respectively. It is shown that the “effective” fluctuation statistics of the signal to be detected is determined completely by the eigenvalues of the matrix Rc-1Rs. For example the signal to be detected has an effective Swerling II fluctuation statistics when all eigenvalues of the above matrix are equal. Swerling I fluctuation statistics results effectively when all eigenvalues except one are equal to zero. Eigenvalue distributions between these two limiting cases correspond to fluctuation statistics that lie between Swerling I and II models 相似文献
4.
J. Denavit 《Space Science Reviews》1985,42(1-2):85-102
This paper presents one-dimensional particle-fluid hybrid simulations in which the strongly collisional components of the
plasma (e.g., ions and thermal electrons with νcfΔt > 1) are treated as fluids and the weakly collisional components (e.g., energetic electrons with νcpΔt ≪ 1) are treated as particles. Here νcf denotes the fluid ion and electron collision frequencies, νcp is the energetic particle collision frequency and Δt is the time step. Collisions between particle and fluid components are
treated by a Monte-Carlo method and mass transfers between the particle and fluid electron components are governed by collision
frequency thresholds. The field is computed implicitly to allow time steps with Ωp Δt > 1 (Ωp: plasma frequency). 相似文献
5.
Based on the experience gained from Sunrayce '95, the Solar Motion Team has made many changes to the design of the next generation solar car. These changes have resulted in a vehicle that is very different from the “Solar Rolar”, The Dakota Sun is a three wheeled vehicle with separate cab and solar array. This design allows for improved aerodynamics, decreased weight, lower rolling resistance, and ease of manufacture compared to the four wheeled catamaran used in the last race. However, this design sacrifices total enclosed wheel base area, additional room for components, and added power from side solar panels, The major objectives for the team's redesigned Sunrayce '97 entry are: systems integration; decrease the weight of the car; decrease aerodynamic drag; more efficient use of available energy; and increased driver safety. The team has set a standard to use the latest available technology. Although this increases the complexity of the components, by using a systems engineering approach the “Dakota Sun” has evolved into a more integrated vehicle. This philosophy of integrated design has resulted in great improvements in mechanical design and manufacturing techniques, as well as electrical innovations. The major design changes evident from the original Sunraycen '95 vehicle are the result of an evolutionary design process that has produced the highly competitive Sunraycel '97 design outlined in this article 相似文献
6.
As a circuit is tested, the current drawn from a power supply can vary as different functions are invoked by the test. The current draw can be plotted against time, showing a characteristic trace for the test performed. Sensors in the ATS power supply can be used to monitor the current flow during test execution. Defective components can be classified using a Neural Network according to the pattern of variation from the “trace” of a good card. This can be performed as a background function, with the network gaining in accuracy over time. This paper discusses the Neural Network Routine for diagnosing circuit faults using monitored power supply current 相似文献
7.
基于三维裂纹特征,本文提出了一种测量孔边角裂纹近门槛区疲劳裂纹扩展速率及门槛值的实验方法。为了得到真实的裂纹形状变化规律,首先针对具体试样用勾线方法建立其“b-a”标定曲线。参照门槛值的标准测试方法,本文仅需测量“a”方向裂纹尺寸,然后用标定曲线换算共相应的“b”方向尺寸。这样我们就可以得到关于“a”和“b”的两组数据,而这两个方向代表孔边角裂纹特征方向。通过分别对30CrMaSiNi2A和2024T3材料的实测研究,证明本文提出的测试方法是可行的。在实验数据基础上,进行了结果的统计对比,得出:1.“a”和“b”方向的近门槛区疲劳裂纹扩展速率及门槛值基本一致;2.孔径大小对实验结果没有影响。;3.同样厚度情况下,孔边角裂纹试样的近门槛区疲劳裂纹扩展速率编高,而门槛值相应较小。 相似文献
8.
Willett P. Alford M. Vannicola V. 《IEEE transactions on aerospace and electronic systems》1994,30(4):986-1000
There has been a great deal of theoretical study into decentralized detection networks composed of similar (often identical), independent sensors, and this has produced a number of satisfying theoretical results. At this point it is perhaps worth asking whether or not there is a great deal of point to such study-certainly two sensors can provide twice the illumination of one, but what does this really translate to in terms of performance? We take as our metric the ground area covered with a specified Neyman-Pearson detection performance. To be fair, the comparison will be of a multisensor network to a single-sensor system where both have the same aggregate transmitter power. The situations examined are by no means exhaustive but are, we believe, representative. Is there a case? The answer, as might be expected, is “sometimes.” When the statistical situation is well behaved there is very little benefit to a fused system; however, when the environment is hostile the gains can be significant. We see, depending on the situation, gains from colocation, gains from separation, optimal gains from operation at a “fusion range,” and sometimes no gains at all 相似文献
9.
Nonparametric methods for clutter removal 总被引:2,自引:0,他引:2
Methods of clutter rejection are discussed which furnish an inherent counterpart of target tracking and detection algorithms. We describe how nonparametric curve estimation methods reduce the original sensor data to a “signal-plus-noise” model which is well suited for various hypotheses testing and dynamical filtering algorithms. We also verify a “white noise” assumption for the model of residuals 相似文献
10.
On measurement of operational security 总被引:1,自引:0,他引:1
Brocklehurst S. Littlewood B. Olovsson T. Jonsson E. 《Aerospace and Electronic Systems Magazine, IEEE》1994,9(10):7-16
Ideally, a measure of the security of a system should capture quantitatively the intuitive notion of “the ability of the system to resist attack.” That is, it should be operational, reflecting the degree to which the system can be expected to remain free of security breaches under particular conditions of operation (including attack). Instead, current security levels at best merely reflect the extensiveness of safeguards introduced during the design and development of a system. Whilst we might expect a system developed to a higher level than another to exhibit “more secure behavior” in operation, this cannot be guaranteed; more particularly, we cannot infer what the actual security behavior will be from knowledge of such a level. In the paper we discuss similarities between reliability and security with the intention of working toward measures of “operational security” similar to those that we have for reliability of systems. Very informally, these measures could involve expressions such as the rate of occurrence of security breaches, or the probability that a specified “mission” can be accomplished without a security breach. This new approach is based on the analogy between system failure and security breach, but it raises several issues which invite empirical investigation. We briefly describe a pilot experiment that we have conducted to judge the feasibility of collecting data to examine these issues 相似文献
11.
Kirubarajan T. Wang H. Bar-Shalom Y. Pattipati K.R. 《IEEE transactions on aerospace and electronic systems》2001,37(2):386-400
We present the development of a multisensor fusion algorithm using multidimensional data association for multitarget tracking. The work is motivated by a large scale surveillance problem, where observations from multiple asynchronous sensors with time-varying sampling intervals (electronically scanned array (ESA) radars) are used for centralized fusion. The combination of multisensor fusion with multidimensional assignment is done so as to maximize the “time-depth” in addition to “sensor-width” for the number S of lists handled by the assignment algorithm. The standard procedure, which associates measurements from the most recently arrived S-1 frames to established tracks, can have, in the case of S sensors, a time-depth of zero. A new technique, which guarantees maximum effectiveness for an S-dimensional data association (S⩾3), i.e., maximum time-depth (S-1) for each sensor without sacrificing the fusion across sensors, is presented. Using a sliding window technique (of length S), the estimates are updated after each frame of measurements. The algorithm provides a systematic approach to automatic track formation, maintenance, and termination for multitarget tracking using multisensor fusion with multidimensional assignment for data association. Estimation results are presented for simulated data for a large scale air-to-ground target tracking problem 相似文献
12.
Rabideau D.J. Steinhardt A.O. 《IEEE transactions on aerospace and electronic systems》1999,35(3):879-891
Adaptive array algorithms based on sample matrix inversion (SMI) require the availability of a secondary data set to “train” the adaptive filter. Numerous data-independent rules have been proposed for selecting this training data. However, such rules often perform poorly in inhomogeneous environments. We present data-adaptive methodologies for selecting the training data. The techniques, called “Power Selected Training” and “Power Selected Deemphasis”, use measurements of the interference environment to select training data. This work describes these algorithms and their performance on recorded radar data 相似文献
13.
Bethel R.E. Paras G.J. Hatfalvi E.J. Skora J.M. 《IEEE transactions on aerospace and electronic systems》1995,31(3):1019-1042
Time delay detection and tracking problems have been investigated in previous papers. The approach used is applicable to many problems. In those papers, a first-order Markov process was assumed for the signal parameter (time delay) dynamic model and a constant signal parameter value was assumed within a “block”, or processing unit of time. A performance degradation is incurred when the signal parameter value is “nearly constant-rate”. Also, “crossing” signal parameter values from different signals cannot be tracked. The detector-trackers will “switch” signals. To combat these difficulties, the signal parameter dynamic model is assumed to be a second-order Markov process, and signal parameter rate of change information is computed within a block. A rate-aided multisignal detection and tracking system is developed with these assumptions 相似文献
14.
15.
近10年来,随着对动态断裂问题的深入研究,出现了众多针对动态裂纹扩展的计算模型,但它们都存在着一定的缺陷。对动态裂纹扩展问题,计算模型的成败取决于解决该问题的变分方程、扩展的模拟方法以及对动态裂纹附近的应力、应变场的表达是否合理。但文献所用的常规元、文献对裂纹扩展使用的“逐步节点力释放”法和文献采用的变分方程“energy consistent variational statement”都存在着某些不合理因素,因此计算结果不很理想。另外,由于模拟裂纹扩展的计算量非常之大,如何在保证精度的前提下节省计算时间也是需要进一步解决的问题。本文力求通过采用新的变分方程、新的奇异元、利用文献的扩展模拟方式克服以上存在的种种不足。 相似文献
16.
A probability density function (pdf) based approach to the multitarget tracking problem is presented. The input data are obtained by measurements over time from a front-end detector. The desired output is the number of targets present and the parameters of each target. The same approach has previously been used for time delay detection and tracking problems and is adapted to this problem This approach is an alternative to the traditional approach of “association” and “tracking” on the measurements 相似文献
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18.
J. L. Linsky 《Space Science Reviews》2007,130(1-4):367-375
Analysis of UV spectra obtained with the HST, FUSE and other satellites provides a new understanding of the deuterium abundance
in the local region of the galactic disk. The wide range of gas-phase D/H measurements obtained outside of the Local Bubble
can now be explained as due to different amounts of deuterium depletion on carbonaceous grains. The total D/H ratio including
deuterium in the gas and dust phases is at least 23 parts per million of hydrogen, which is providing a challenge to models
of galactic chemical evolution. Analysis of HST and ground-based spectra of many lines of sight to stars within the Local
Bubble have identified interstellar velocity components that are consistent with more than 15 velocity vectors. We have identified
the structures of 15 nearby warm interstellar clouds on the basis of these velocity vectors and common temperatures and depletions.
We estimate the distances and masses of these clouds and compare their locations with cold interstellar clouds. 相似文献
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20.
The development of a strapdown inertial navigation system (SINS) for aerodynamically controlled vehicles, which are limited to altitudes below 30 km (that is, a small distance compared with the Earth's radius of about 7000 km), or using the so-called flat-Earth model (FEM), is the principal objective of this work. In dealing with the FEM equations, the north, east, down (NED) frame on the surface of the Earth is taken as an inertial reference frame. Although, this frame is both accelerating and rotating, the accelerations associated with the Earth's rotation are negligible compared with the acceleration that can be produced by a maneuvering aircraft. Also, in this model, the gravity is taken as constant. In developing the SINS for the FEM, the aerodynamic force and moment have dominant roles, depending primarily on such variables as the angle of attack and sideslip, their derivatives, components of the angular velocity of the aircraft, and the control inputs. On the other hand, the SINS deals with such variables as the small-angle rotation vectors. Thus, it was necessary to link both set of variables as state variables of the strapdown FEM as is done in this work. The developed model is relevant for small (less than 200) angles of attack and sideslip. 相似文献