面向对象分析的非结构化背景目标高光谱探测方法研究

针对非结构化背景探测器中背景协方差矩阵估计的局限性,提出了一种基于面向对象分析的高光谱小目标探测算法。首先对图像进行自适应迭代分割处理,将其划分为许多均质对象;然后进行正态最优分布选取,利用多元正态无偏检验选取最佳对象集;最后将此数据集合作为局部背景并结合GLR基准算法进行目标探测。该算法可以使局部背景最大化的服从正态分布,有效地将背景光谱信息和目标光谱信息分离开来,同时通过最优选取过程克服了目标信息“污染”问题。为了验证算法的有效性,利用真实的OMIS数据进行仿真实验,并与非结构化背景探测器GLR和基于K-Means聚类的改进GLR算法的检测结果比较,结果表明提出的算法具有良好的探测性能和较低的虚警概率。     

Acoustic detection of North Atlantic right whale contact calls using spectrogram-based statistics

This paper considers the problem of detection of contact calls produced by the critically endangered North Atlantic right whale, Eubalaena glacialis. To reduce computational time, the class of acceptable detectors is constrained by the detectors implemented as a bank of two-dimensional linear FIR filters and using the data spectrogram as the input. The closed form representations for the detectors are derived and the detection performance is compared with that of the generalized likelihood ratio test (GLRT) detector. The test results demonstrate that in the presence of impulsive noise, the spectrogram-based detector using the French hat wavelet as the filter kernel outperforms the GLRT detector and decreases computational time by a factor of 6.     

浅海环境中的匹配模态空间检测器

将水下声传播规律融入到算法设计中可以有效提高被动声呐目标检测性能。当声源位置未知时,广义似然比检测器和贝叶斯检测器分别通过搜索和积分的方式来消除声源位置不确定性的影响。但是,基于有限个信号波前实现的广义似然比检测器和贝叶斯检测器在某些声源位置上存在性能大幅下降的问题。为此,利用水下声传播的物理特性,提出了一种稳健的子空间检测器——匹配模态空间检测器,稳健的意义在于:当阵列获取到的辐射声信号能量给定时,检测器可以在不同声源位置情况下提供相同的检测性能。该检测器通过模态空间一定程度上利用了海洋环境知识,获得了比具有相同稳健性的能量检测器更好的检测性能。典型浅海环境中的仿真实验对比结果表明:匹配模态空间检测器相比广义似然比检测器和贝叶斯检测器的峰值性能下降较小、所需的计算量更少、对环境失配的宽容性更好。      

Study of a nTHGEM-based thermal neutron detector

With new generation neutron sources, traditional neutron detectors cannot satisfy the demands of the applications, especially under high flux. Furthermore, facing the global crisis in ~3He gas supply, research on new types of neutron detector as an alternative to ~3He is a research hotspot in the field of particle detection. GEM(Gaseous Electron Multiplier) neutron detectors have high counting rate, good spatial and time resolution, and could be one future direction of the development of neutron detectors. In this paper, the physical process of neutron detection is simulated with Geant 4 code, studying the relations between thermal conversion efficiency, boron thickness and number of boron layers. Due to the special characteristics of neutron detection, we have developed a novel type of special ceramic n THGEM(neutron THick GEM) for neutron detection. The performance of the n THGEM working in different Ar/CO_2 mixtures is presented, including measurements of the gain and the count rate plateau using a copper target X-ray source. A detector with a single n THGEM has been tested for 2-D imaging using a ~(252)Cf neutron source. The key parameters of the performance of the n THGEM detector have been obtained, providing necessary experimental data as a reference for further research on this detector.     

Underwater source detection using a spatial stationarity test

The problem of detecting a source in shallow water is addressed. The complexity of such a propagation channel makes precise modeling practically impossible. This lack of accuracy causes a deterioration in the performance of the optimal detector and motivates the search for suboptimal detectors which are insensitive to uncertainties in the propagation model. A novel, robust detector which measures the degree of spatial stationarity of a received field is presented. It exploits the fact that a signal propagating in a bounded channel induces spatial nonstationarity to a higher degree than mere background noise. The performance of the proposed detector is evaluated using both simulated data and experimental data collected in the Mediterranean Sea. This performance is compared to those of three other detectors, employing different extents of prior information. It is shown that when the propagation channel is not completely known, as is the case of the experimental data, the novel detector outperforms the others in terms of threshold signal-to-noise ratio (SNR). In the presence of environmental mismatch, the threshold SNR of the novel detector for the experimental data appears 2-5 dB lower than the other detectors. That is, this detector couples good performance with robustness to propagation uncertainties.     

Nonuniformity correction algorithm based on adaptive filter for infrared focal plane arrays

Response nonuniformity is a key problem that influences the imaging performance of infrared focal plane arrays (IRFPA) imaging system. A parallel processing algorithm to adaptively estimate the nonuniformity correction (NUC) parameters for IRFPA is presented. In this algorithm, a bank of the adaptive filter is applied to adaptively estimate the NUC parameters for every detector in IRFPA. The infrared image sequences are input into the bank of adaptive filter. After certain times recursion calculations are executed frame-by-frame, then the optimal coefficients of the gain and the offset of detector in IRFPA are achieved. Then the NUC is fulfilled ultimately. The algorithm reduces the influence that the response drift with time imposed on NUC effectively, and achieves good NUC effect. It was validated by real experimental imaging procedures.     

基于自适应滤波的红外焦平面阵列非均匀性校正算法

 红外探测器响应漂移特性会降低红外焦平面阵列（IRFPA）非均匀性校正的精度。针对该问题提出了一种基于场景的IRFPA非均匀性校正算法。该算法利用所获得的序列成像场景信息,采用一种基于快速自适应滤波器的最优化递归估计方法来获得非均匀性校正参数,并利用当前的成像信息来更新校正参数,以此降低探测器响应漂移特性对非均匀性校正的影响。算法仿真实验显示,对非线性参数为26.12%的同一图像,使用该算法、两点校正算法和卡尔曼滤波校正算法校正1 h后,可分别将非线性参数降至1.856%,3.122%和1.893%,说明该算法可获得稳定而较好的非均匀性校正效果。     

Optoelectronic Devices: Design,Modeling, and Simulation,by Xun Li

A historical survey of the development of solid-state detectors is given, and it is shown why semiconductor detectors are superior to the earlier crystal counters. The physical processes which occur during the detection of nuclear radiation in a solid-state device are considered in detail, and the merits of the reverse-biased semiconductor junction in silicon or germanium are set out. Factors which determine the energy resolution of such a detector are analysed, and also the effects of radiation damage. The preparation of such detectors is not treated in detail, but the physical principles on which the important types of detector depend are described. The final section surveys the field of applications of solid-state detectors in nuclear physics, radiochemical analysis, space research, medicine and biology.     

Quantitative performance measurements of bent crystal Laue analyzers for X‐ray fluorescence spectroscopy

Third‐generation synchrotron radiation sources pose difficult challenges for energy‐dispersive detectors for XAFS because of their count rate limitations. One solution to this problem is the bent crystal Laue analyzer (BCLA), which removes most of the undesired scatter and fluorescence before it reaches the detector, effectively eliminating detector saturation due to background. In this paper experimental measurements of BCLA performance in conjunction with a 13‐element germanium detector, and a quantitative analysis of the signal‐to‐noise improvement of BCLAs are presented. The performance of BCLAs are compared with filters and slits.     

Search for astro-gravitational correlations

A special arrangement of a gravity-wave experiment, in which the noise background of the gravity detector is investigated near time markers corresponding to the detection of astrophysical events accompanying neutron or gamma bursts, is studied. A general algorithm is developed for analyzing the traces for the case of resonant solid-state detectors. The efficiency of the algorithm is demonstrated in a reanalysis of old data concerning the “neutron-gravity correlation” effect associated with the explosion of the SN1987A Supernova. Modifications of the algorithm for searching for gamma-gravity correlations are proposed.     

Measuring partial fluorescence yield using filtered detectors

Typically, X‐ray absorption near‐edge structure measurements aim to probe the linear attenuation coefficient. These measurements are often carried out using partial fluorescence yield techniques that rely on detectors having photon energy discrimination improving the sensitivity and the signal‐to‐background ratio of the measured spectra. However, measuring the partial fluorescence yield in the soft X‐ray regime with reasonable efficiency requires solid‐state detectors, which have limitations due to the inherent dead‐time while measuring. Alternatively, many of the available detectors that are not energy dispersive do not suffer from photon count rate limitations. A filter placed in front of one of these detectors will make the energy‐dependent efficiency non‐linear, thereby changing the responsivity of the detector. It is shown that using an array of filtered X‐ray detectors is a viable method for measuring soft X‐ray partial fluorescence yield spectra without dead‐time. The feasibility of this technique is further demonstrated using α‐Fe₂O₃ as an example and it is shown that this detector technology could vastly improve the photon collection efficiency at synchrotrons and that these detectors will allow experiments to be completed with a much lower photon flux reducing X‐ray‐induced damage.     

Trading detection for resolution in active sonar receivers

This paper proposes an active sonar receivers that offers a smooth trade-off between detection and resolution. A matched filter is the optimal detector of known signals in white Gaussian noise but may fail to resolve the targets if the time separation of targets is less than the mainlobe width of the autocorrelation function of the transmitted signal. An inverse filter achieves optimal resolution performance for multiple targets in the absence of noise, but amplifies the noise outside the signal bandwidth in a manner that makes it impractical in many realistic scenarios. The proposed active sonar receiver, the variable resolution and detection receiver (VRDR) combines the matched and inverse filter properties to achieve a smooth trade-off between detection and resolution. Simulated receiver operating characteristics demonstrate that for a range of dipole sonar targets, the performance of the VRDR is superior to the matched and inverse filter, as well as another previously proposed bandlimited inverse filter.     

Multiple access interference rejection in OCDMA using a two-photon absorption based semiconductor device

An experimental demonstration of a two-channel OCDMA system with detection performed using standard linear detection or a TPA-based nonlinear detector is presented. These results show an improvement in the extinction ratio of the decoded signal by ∼5 dB using TPA detection. A simulation model of the TPA detector used during the experiments was created and used in a four-channel OCDMA system simulation using both linear and nonlinear detection methods. The simulation results show that error-free performance is achievable for a 4-user system using the nonlinear TPA detector while the OCDMA system employing linear detection is severely limited by the effects of noise generated by adjacent optical channels (multiple access interference).     

HOT infrared photodetectors

At present, uncooled thermal detector focal plane arrays are successfully used in staring thermal imagers. However, the performance of thermal detectors is modest, they suffer from slow response and they are not very useful in applications requiring multispectral detection. Infrared (IR) photon detectors are typically operated at cryogenic temperatures to decrease the noise of the detector arising from various mechanisms associated with the narrow band gap. There are considerable efforts to decrease system cost, size, weight, and power consumption to increase the operating temperature in so-called high-operating-temperature (HOT) detectors. Initial efforts were concentrated on photoconductors and photoelectromagnetic detectors. Next, several ways to achieve HOT detector operation have been elaborated including non-equilibrium detector design with Auger suppression and optical immersion. Recently, a new strategies used to achieve HOT detectors include barrier structures such as nBn, material improvement to lower generation-recombination leakage mechanisms, alternate materials such as superlattices and cascade infrared devices. Another method to reduce detector’s dark current is reducing volume of detector material via a concept of photon trapping detector. In this paper, a number of concepts to improve performance of photon detectors operating at near room temperature are presented. Mostly three types of detector materials are considered — HgCdTe and InAsSb ternary alloys, and type-II InAs/GaSb superlattice. Recently, advanced heterojunction photovoltaic detectors have been developed. Novel HOT detector designs, so called interband cascade infrared detectors, have emerged as competitors of HgCdTe photodetectors.     

New log-t-based CFAR detectors for a non-homogeneous Weibull Background

Based on new log-t-based detectors, we propose to improve the detection performances of the log-t-Constant False Alarm Rate (log-t-CFAR) detector for a non-homogeneous Weibull background. This paper is twofold. We first resort to the Automatic Constant False Censoring Rate (CFCR) algorithm, which guarantees an accurate rejection of an a priori unknown number of outliers. That is, we introduce two hybrid detectors by coupling the log-t-CFAR algorithm to the Maximum Likelihood-CFCR (MLE-CFCR) algorithm, yielding the H-MLE/log-t-CFAR detector, and to the Weber-Haykin Constant False Censoring Rate (WH-CFCR) algorithm, yielding the H-WH/log-t-CFAR detector. Then, based on the Variability Index (VI) as a background discriminator, we propose the Switching VI-log-t-CFAR (SVI-log-t-CFAR) detector. Thus, depending on the background heterogeneity, this detector has the capability to switch automatically to the appropriate detector; namely, the log-t-CFAR detector, in case of a homogeneous background, either one of the hybrid detectors, in case of the presence of outliers or the Automatic Edge Censoring log-t-CFAR (AEC-log-t-CFAR) detector, in case of the presence of a clutter edge. We assess the efficiency of these detectors through intensive Monte Carlo simulations. We show that, while no additional detection performances are observed in a homogeneous background, the new detectors exhibit a significant CFAR gain with respect to the log-t-CFAR detector in the presence of any inhomogeneity within the reference window.     

基于视神经网络的混沌时间序列奇异信号实时检测算法

提出了一种基于视神经网络的实时检测混沌时间序列中的奇异点算法,设计了视神经网络奇异点检测器(RNNND);然后设计了基于反向传播(BP)神经网络和径向基函数(RBF)神经网络的混沌时间序列奇异点检测器.利用Lorenz理论模型产生的时间序列和实测输油管道压力时间序列分别检验了这3个奇异点检测器在抗干扰能力、检测微弱信号能力和运算速度等方面的性能.仿真和分析表明,RNNND具有良好的检测精度和较快检测速度.最后详细分析了3种奇异点检测器优缺点并给出了适用场合.     

Gamma detectors in explosives and narcotics detection systems

Gamma detectors based on BGO crystals were designed and developed at the Joint Institute for Nuclear Research. These detectors are used in explosives and narcotics detection systems. Key specifications and design features of the detectors are presented. A software temperature-compensation method that makes it possible to stabilize the gamma detector response and operate the detector in a temperature range from ?20 to 50°C is described.     

Pulse shape simulation for segmented true-coaxial HPGe detectors

A new package to simulate the formation of electrical pulses in segmented true-coaxial high purity germanium detectors is presented. The computation of the electric field and weighting potentials inside the detector as well as of the trajectories of the charge carriers is described. In addition, the treatment of bandwidth limitations and noise are discussed. Comparison of simulated to measured pulses, obtained from an 18-fold segmented detector operated inside a cryogenic test facility, are presented.     

M-ary information processing via an optimal nonlinear detector

This paper presents a novel approach of M-ary baseband pulse amplitude modulated signal processing via a parameter-optimized nonlinear dynamic system.This nonlinear system usually shows the phenomenon of stochastic resonance by adding noise.To thoroughly discuss the signal processing performance of the nonlinear system,we tune the system parameters to obtain a nonlinear detector with optimal performance.For characterizing the output of the nonlinear system,the derivation of the probability of detection error is given by the system response speed and the probability density function of the nonlinear system output.By varying the noise intensity with fixed system parameters,the phenomenon of stochastic resonance is shown and by tuning the system parameters with fixed noise,the probability of detection error is minimized and the nonlinear system is optimized.The detection performance of the two cases is compared with the theoretical probability of detection error,which is validated by numerical simulation.     

A dose meter for pulsed neutron fields

Many active radiation detectors exhibit severe limitations in pulsed radiation fields, which cannot be easily overcome without the design of new technology. Therefore a new area dose monitor for the measurement of pulsed and continuous neutron and gamma radiation fields was developed. The measurement of pulsed radiation is based on activation of short-lived nuclides in the detector materials or in the surroundings. The instrument comprises a thermal neutron detector in a moderator for neutron detection and a plastic scintillator for beta and gamma detection. These detectors are measuring direct radiation and also decay particles from the instable activated nuclei. The data are time-resolved acquired by a fast FADC module and the delayed decay products are identified by analyzing their timing characteristics. Measurements with pulsed and with continuous radiation are reported.