Target tracking based on frequency spectrum amplitude

The amplitude of frequency spectrum can he integrated with prohabilisfic data association （PDA） to distinguish the target with clutter echoes, especially in low SNR underwater environment. A new target-tracking algorithm is presented which adopts the amplitude of frequency spectrum to improve target tracking in clutter. The prohabilisfic density distribution of frequency spectrum amplitude is analyzed. By simulation, the results show that the algorithm is superior to PDA. This approach enhances stability for the association probability and increases the performance of target tracking.

EFFICIENT STRIP-MODE SAR RAW SIGNAL SIMULATION OF MIXED TARGETS BASED ON ACCURATE 2-D SPECTRUM

An accurate and efficient Synthetic Aperture Radar(SAR)raw data generator is of considerable value for testing system parameters and verifying imaging algorithms.Nevertheless,the existing simulator cannot exactly handle the case of the fast moving targets in high squint geometry.As for the issue,the analytical expression for the two Dimensional(2-D)signal spectrum of moving targets is derived and a fast raw echo simulation method is proposed in this study.The proposed simulator can accommodate the moving targets in the high squint geometry,whose processing steps of the simulation are given in detail and its computational complexity is analyzed.The simulation data for static and moving targets are processed and analyzed,and the results are given to validate the effectiveness of the proposed approach.

Line spectrum detection algorithm based on the phase feature of target radiated noise

In order to improve the performance of line spectrum detection,according to the feature that the underwater target radiated noise containing stable line spectrum,the differences of the phase difference between line spectrum and background noise,a weighted line spectrum detection algorithm based on the phase variance is proposed in frequency domain.After phase difference alignment,the phase variance of line spectrum and the phase of background noise,respectively,are small and big in frequency domain,this method utilizes the weighted statistical algorithm to cumulate the frequency spectrum based on the phase variance,which can restrain the background noise disturbance,and enhance the signal to noise ratio（SNR）.The theory analysis and experimental results both verify that the proposed method can well enhance the energy of line spectrum,restrain the energy of background noise,and have better detection performance under lower SNR.

Selection and modification of ground motion records using Newmark-Hall spectrum as target spectrum for long-period structures

Input ground motions have significant impacts on the uncertainty of structural responses in time-history analysis.In this study,records were selected and scaled for the evaluation of mean structural responses according to the target spectrum.The Newmark-Hall spectrum is closely related to seismic response of short,medium and long-period structures,so it was taken as the target spectrum here.The nonlinear time-history analyses of 9-story and 20-story steel moment-resisting frame structures were carried out as examples.They represent medium and long-period buildings,respectively.Three target spectra with risk of 50%,10%and 2%probabilities for exceedance in 50 years were calculated by the average Newmark-Hall spectrum method for three ground motion sets developed in the SAC Steel Project.The predicted structural mean responses of these Newmark-Hall spectra were compared with those calculated by the average spectral acceleration method for the same record set.It is found that both methods have similar accuracy for estimating the structural mean response.However,the method proposed herein is more effective in reducing the variability of the structural responses.Also,the proposed method is more advantageous for the time-history analysis of long-period structures or structures with more severe nonlinear responses under strong seismic excitations.

A method of line spectrum extraction based on target radiated spectrum feature and its post-processing

To improve the ability of detecting underwater targets under strong wideband interference environment,an efficient method of line spectrum extraction is proposed,which fully utilizes the feature of the target spectrum that the high intense and stable line spectrum is superimposed on the wide continuous spectrum.This method modifies the traditional beam forming algorithm by calculating and fusing the beam forming results at multi-frequency band and multi-azimuth interval,showing an excellent way to extract the line spectrum when the interference and the target are not in the same azimuth interval simultaneously.Statistical efficiency of the estimated azimuth variance and corresponding power of the line spectrum band depends on the line spectra ratio(LSR)of the line spectrum.The change laws of the output signal to noise ratio(SNR)with the LSR,the input SNR,the integration time and the filtering bandwidth of different algorithms bring the selection principle of the critical LSR.As the basis,the detection gain of wideband energy integration and the narrowband line spectrum algorithm are theoretically analyzed.The simulation detection gain demonstrates a good match with the theoretical model.The application conditions of all methods are verified by the receiver operating characteristic(ROC)curve and experimental data from Qiandao Lake.In fact,combining the two methods for target detection reduces the missed detection rate.The proposed post-processing method in2-dimension with the Kalman filter in the time dimension and the background equalization algorithm in the azimuth dimension makes use of the strong correlation between adjacent frames,could further remove background fluctuation and improve the display effect.

Special algorithm of enhancing underwater targetradiated dynamic line spectrum

Performance of traditional adaptive line enhancer （ALE） in suppressing Gaussian noise is low and can get worse at low input signal-to-noise ratio（SNR）. For greatly overcoming these disadvantages, feature of fourth-order cumulant （FOC） different slices for quasi-stationary random process is analyzed, fourth order cumulant（FOC） different slice-based adaptive dynamic line enhancer is presented, and output SNR of the proposed enhancer is derived and bigger than that of the ALE via theoretical analysis. Simulation tests with the underwater moving target-radiated data have shown that the proposed enhancer outperforms the ALE in suppressing Gaussian noise and enhancing dynamic line spectrum feature.

SAR target detection based on the optimal fractional Gabor spectrum feature

In this paper,an algorithm based on a fractional time-frequency spectrum feature is proposed to improve the accuracy of synthetic aperture radar(SAR)target detection.By extending the fractional Gabor transform(FrGT)into two dimensions,the fractional time-frequency spectrum feature of an image can be obtained.In the achievement process,we search for the optimal order and design the optimal window function to accomplish the two-dimensional optimal FrGT.Finally,the energy attenuation gradient(EAG)feature of the optimal time-frequency spectrum is extracted for high-frequency detection.The simulation results show the proposed algorithm has a good performance in SAR target detection and lays the foundation for recognition.

Spectral Target-Detecting System Using Sine-Wave Modulation

Target detection is one of the key technology of precision chemical application.Previously the digital coding modulation technique was commonly used to emit and receive the optical signal in the target detection systems previously in China.It was difficult to adjust the output power,and the anti-interference ability was weak in these systems.In order to resolve these problems,the target detection method based on analog sine-wave modulation was studied.The spectral detecting system was set up in the aspects of working principle,electric circuit,and optical path.Lab testing was performed.The results showed that the reflected signal from the target varied inversely with detection distances.It indicated that it was feasible to establish the target detection system using analog sine-wave modulation technology.Furthermore,quantitative measurement of the reflected optical signal for near-infrared and visible light could be achieved by using this system.The research laid the foundation for the future development of the corresponding instrument.

MEASUREMENT OF NEUTRON SPECTRA FROM THICK Be TARGET BOMBARDED WITH DEUTERONS

Neutron spectra of Be(d,n) reaction were measured for deuteron energies from 13.5 to 22 MeV by using a stilbene scintillator detector and flight time technique.A special calibration method of neutron detector efficiency for higher energy portion was adopted. The spectral neutron yield per unit beam charge on the Be target at 0° was determined. The fluence-averaged mean neutron energies of the neutron spectra are given as a function of the incident energy for several thresholds. The measured neutron spectra have an almost same shape at different incident deuteron energies. High energy portion (En】1.8MeV) and low energy portion (En【2.0MeV)of the neutron spectra were separately measured and they were concerned with each other by normalization. The energy range of whole neutron spectra is 0.7 MeV to 30MeV.

Neutronic analysis of deuteron-driven spallation target

Deuteron-driven spallation targets have garnered attention recently because they can provide high-energy neutrons to transmute long-lifetime fission products.In this study,the Geant4 toolkit was used to simulate the inter-action between a deuteron beam at 500 MeV and a com-posite target composed of alternating lead-bismuth eutectic(LBE)and water.The water was used because it may be employed as a target coolant.The energy spectrum,neu-tron yield,average energy,and total energy of the emitted neutrons were calculated for different thicknesses and thickness ratios between the LBE and water.For a constant target thickness,the neutron yield increases with an increasing thickness ratio of LBE to H 2 O,while the aver-age energy of the emitted neutrons decreases with an increasing in the aforementioned thickness ratio.These two aspects support the use of a pure target,either LBE or water.However,with an increasing LBE-to-H 2 O thickness ratio,the total energy of the emitted neutrons increases and then decreases.This result supports the addition of water into the LBE target.The angular distributions of the emitted neutrons show that the rear of the target is suit-able for loading nuclear waste containing minor actinides and long-lifetime fission products.

Classification of birds and drones by exploiting periodical motions in Doppler spectrum series

With the rapidly growing abuse of drones, monitoring and classification of birds and drones have become a crucial safety issue. With similar low radar cross sections(RCSs), velocities, and heights, drones are usually difficult to be distinguished from birds in radar measurements. In this paper, we propose to exploit different periodical motions of birds and drones from highresolution Doppler spectrum sequences(DSSs) for classification.This paper presents an elaborate feature vector representing the periodic fluctuations of RCS and micro kinematics. Fed by the Doppler spectrum and feature sequence, the long to short-time memory(LSTM) is used to solve the time series classification.Different classification schemes to exploit the Doppler spectrum series are validated and compared by extensive real-data experiments, which confirms the effectiveness and superiorities of the proposed algorithm.

Experimental investigation of laser-produced-plasma EUV source based on liquid target

A laser-produced plasma(LPP) source was built using liquid as target and a Nd:YAG laser as the irradiation laser, and the LPP source's radiation with ethanol and acetone target respectively was measured by an AXUV100 silicon photodiode combined with a McPHERSON model 247 grazing incidence monochromator of the resolution Δλ≤0.075 nm and the wavelength scanning interval 0.5 nm. Both ethanol and acetone target LPP source had EUV emission at 11～20 nm wavelength. The comparison between the spectra of the two kinds of target materials shows that all the two kinds of target source's spectra are the result of oxygen ions' transitions under current source's parameters, but the spectrum intensity from different target sources is different. The spectra intensity from the ethanol target is higher than that from the acetone target. In addition, the target liquid is forced into the vacuum chamber by the background pressure supported by the connected external high pressure gas, and the influence of the background pressure on the source's intensity is investigated.

阿南德氏链霉菌FXJ-25的鉴定及对烟草靶斑病的防效

为筛选烟草靶斑病菌拮抗菌,丰富烟草靶斑病生防资源,采用稀释涂布法和平板对峙法进行放线菌分离,筛选得到一株具有明显拮抗效果的菌株FXJ-25。基于培养特性、生理生化特性及16S rDNA基因序列分析相结合的方法对该菌株进行鉴定,分析了其诱导烟草抗性的能力,并通过盆栽试验对其防效进行了研究。结果表明,拮抗菌FXJ-25对烟草靶斑病菌的抑菌率为74.14%,可引起菌丝畸形,经鉴定该菌株为阿南德氏链霉菌(Streptomyces anandii)。FXJ-25具有广谱抗真菌活性,对瓜类蔓枯病菌(Stagonosporopsis cucurbitacearum)、烟草喀斯特炭疽菌(Colletotrichum karstii)和小麦赤霉病菌(Fusarium graminearum)等15种植物病原真菌均具有较好的拮抗作用,抑菌率在53.43%~100%之间。菌株发酵液还可显著提高烟苗苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、多酚氧化酶(PPO)和过氧化氢酶(CAT)等防御相关酶的活性。盆栽防效中,菌株FXJ-25活菌液(108孢子/mL)对烟草靶斑病具有78.81%的防效。因此,FXJ-25可作为烟草靶斑病的生防材料进一步开发利用。

基于功率谱流形的信息几何DP-TBD算法

针对复杂杂波背景下目标信杂比起伏而导致的漏检问题,本文结合信息几何检测器的性能优势与动态规划检测前跟踪(Dynamic Programming Track Before Detect,DP-TBD)的多帧信息积累能力,提出了基于功率谱流形的信息几何DP-TBD算法.该算法利用功率谱流形与矩阵流形对偶关系,设计了功率谱信息几何检测器,将信息几何检测器的计算复杂度降低了近两个数量级.通过实测数据实验验证,功率谱DP-TBD算法可实现与矩阵DP-TBD算法相近的检测性能,并将运算时间降低为矩阵DP-TBD算法的3%~8%.此外,相较于信息几何检测器,功率谱DP-TBD可将检测信杂比(Signal-to-Clutter Ratio,SCR)提高2~3 dB.

复杂环境下电磁目标信号认知处理架构与应用研究

针对现代电磁频谱设备或终端具有网络化、捷变性、多功能、自适应、种类复杂多样和使用环境复杂多变等特性给认知电磁频谱战系统的信号分析与处理带来的巨大挑战的问题,提出了一种结合人工智能、适合复杂电磁环境下电磁目标信号认知处理与分析的架构。在该架构下电磁目标信号分析与处理被分为目标信号参数估计、目标信号类型分类、辐射源个体识别和目标信号的特征建库与知识图谱[1-3]的构建等4个层次,可以很好适应闭集和开集电磁目标信号的分析与处理;此外,在此架构下提出了未知辐射源辨识、跨模态辐射源智能识别和电磁辐射源的个体识别的算法框架,在实测数据集上的验证实验表明,该算法在闭集和开集电磁信号分析中有效可行。

基于CNN和DCGAN的小样本船舶辐射噪声识别方法

文中建立一种基于卷积神经网络(convolutional neural networks,CNN)和深度卷积生成对抗网络(deep convolutional generative adversarial networks,DCGAN)的船舶目标识别方法.通过采集的船舶辐射噪声数据,以梅尔频谱(Mel spectrogram)作为网络的输入特征,使用DCGAN网络对频谱变换后的样本进行扩充,利用微调的VGG16(visual geometry group)网络实现船舶目标分类,实现了网络收敛速度的提升和训练时间的减少.结果表明:采用所提方法可以生成较高质量的频谱样本,提高船舶辐射噪声识别的准确率.

基于时-频注意力机制网络的水声目标线谱增强

为提高被动声纳对水下低噪声安静型目标的检测,研究者开始关注基于深度学习的线谱增强方法,其中,基于LSTM的线谱增强网络由于同时具有时域和频域的非线性处理能力,具有很强的灵活性,然而其性能还需要进一步提升。为此,该文提出了基于时-频注意力机制的网络模型(TFA-Net),通过在LSTM模型的基础上同时增加时域注意力机制和频域注意力机制,充分利用了目标信号在时域和频域的双重重要特征,提升了对LOFAR谱的线谱增强效果。TFA-Net中的时域注意力机制利用LSTM隐藏状态之间的关联性,增加了模型在时域的注意力,频率注意力机制通过将深度残差收缩网络中收缩子网络的全链接层设计为1维卷积层,增加了模型在频域的注意力。相比于LSTM,TFA-Net具有更高的系统信噪比增益:在输入信噪比为–3 dB的情况下,将系统信噪比增益由2.17 dB提升到12.56 dB;在输入信噪比为–11 dB的情况下,将系统信噪比增益由0.71 dB提升到10.6 dB。仿真和实测数据的实验结果表明,TFA-Net可以有效提升LOFAR谱的线谱增强效果,解决低信噪比下水下目标的检测问题。

高速动能弹撞击装甲结构引起的螺栓连接失效及部件过载损伤研究

目的 验证和揭示高速动能弹对装甲结构的损伤机理。方法 聚焦高速动能弹打击装甲目标时,弹道冲击造成的靶标结构连接失效及部件过载损伤这2种损伤效应,以典型螺栓连接为研究对象,采用高速球形弹丸撞击螺栓连接结构的小尺寸试验对数值模拟方法和材料模型参数进行校验。在此基础上,采用数值模拟和冲击响应谱分析方法对高速动能弹打击全尺寸坦克进行模拟分析,获得撞击过程螺栓连接失效特征、主要影响因素及坦克典型位置部件的冲击加速度曲线和冲击响应谱曲线。结果 在小尺寸试验中,动能输入为0.042MJ时,螺栓连接未发生失效;但25.6MJ动能输入全尺寸坦克时,螺栓发生断裂而使连接失效。数值模拟结果揭示了螺栓发生断裂的主要原因。结论 输入动能大小、连接螺栓直径、模拟设备部件质量和撞击位置为螺栓是否断裂的主要影响因素。坦克某些位置的冲击响应谱曲线高于军用标准给出的临界曲线的下限甚至上限,表明这些位置的部件因高过载损伤导致失效的概率较高。

功率谱密度消频散变换被动估计脉冲声源距离

浅海中传播的低频声波具有多模态特征和频散效应。对接收声信号消频散变换(DDT)可以消除频散效应,实现被动估计声源距离。针对消频散变换存在的测距多值问题,该文提出一种利用功率谱密度消频散变换的被动测距方法(PSD-DDT)。首先使用声场模型KRAKEN计算模态的水平波数;其次在只知道波导不变量大概范围的情况下,估计两个模态之间的频散常数;然后对保留了模态间干涉项的功率谱密度进行消频散变换;最后获得目标距离的估计值为PSD-DDT极大值对应的自变量与频散常数的比值。另外,当海洋参数未知时,需要分别对待测声源和引导声源进行PSD-DDT,利用自变量的比值确定声源距离,这种方法不需要估计频散常数。通过仿真和海试验证了PSD-DDT方法被动测距的有效性,并分析了波导不变量、模态阶数、噪声等因素对距离估计结果的影响。基于黄海试验结果,与DDT方法相比,PSD-DDT的测距误差下降了约49.2%。在35 km范围内最优波导不变量对应的平均相对误差约2.55%,被动测距精度较高。

高通量快堆辐照生产^(252)Cf关键因素分析

^(252)Cf放射源是一种高强度同位素中子源,在科学研究、装置研发等领域具有重大需求,但长期以来依赖于进口。基于高通量快堆初步设计方案开展辐照靶件设计,结合模拟计算结果得出影响^(252)Cf核素生产的关键因素。在5×10^(15)n·cm^(-2)·s^(-1)中子通量水平下,对三种采用不同氢化锆和Eu_(2)O_(3)吸收体辐照靶件设计方案进行裂变沉积能、能谱计算,并通过燃耗计算程序开展重锔、轻锔靶件燃耗计算,与美国辐照生产^(252)Cf实验值对比。结果表明:方案3的计算值与基准值吻合较好且最适用于重锔靶辐照生产^(252)Cf,方案2适用于通过短的辐照周期辐照生产重锔核素。本文的计算与分析可为高通量快堆辐照生产^(252)Cf提供理论与技术支撑。