多普勒效应对雷电源辐射定位的影响

利用电磁辐射信号进行雷电源探测和定位是当前雷电研究的重要探测手段,其定位结果的准确性对正确认识闪电的放电机理非常重要。本文通过数学推导建立了多普勒效应在球坐标下的定位影响理论模型;用Matlab软件进行模拟,分析了多普勒效应对阵列接收信号的影响及误差,研究了多普勒效应对运动雷电源定位结果产生的影响。研究结果表明,多普勒效应对于不同类型、不同距离、不同高度的闪电影响程度不同;根据雷电发展的不同阶段,雷电源的运动速度不同,多普勒效应带来的误差也不同,且其带来的误差是不可忽略的。该研究对实现更高时空分辨力的运动雷电源定位结果和雷电的精细化研究具有重要意义。     

差分多普勒无源定位

论述多普勒频率差无源定位技术的实现方法 ,对等多普勒定位曲线误差进行分析 ,利用LMF(Levenberg -Marquardt-Fletcher)算法求解辐射源位置。在三运动平台条件下 ,通过计算机仿真 (按照MonteCarlo方法 )对算法的定位精度和性能作了评估。     

差分多普勒定位技术的仿真研究

为了研究多个运动平台对固定辐射源的差分多普勒(FDOA)定位,根据FDOA定位原理在"XX系统仿真"平台下建立了平面三站FDOA定位系统仿真模型.首先介绍了定位系统的每个子模块的功能和相应的数学模型;然后对定位误差的Cramer-Rao界进行了公式推导;通过仿真实验考察配置方式、运动方向以及取样数等参数对FDOA定位精度的影响.仿真结果表明所建立的仿真模型是可行而有效的.     

电源的雷电浪涌效应及加固技术研究

雷电浪涌是雷电对电子系统的一种重要的作用形式。雷电对电子系统的影响主要表现在对电源电路的浪涌破坏和干扰上。为研究雷电浪涌对电源的冲击效应,进行了雷电浪涌对直流电源的冲击实验。实验表明,雷电浪涌对直流电源有很大的干扰作用,可使电源产生大的波动或高频噪声。在雷电流涌冲击实验的基础上,对直流电源进行了加固实验,并取得了良好的效果。     

利用多普勒信息的无源相干定位技术

利用多普勒频率信息的第三方辐射源对动目标的无源相干定位技术，可获得高精度无模糊等优越的系统性能。在噪声环境中对动目标定位技术通常要求从系统的可观测性，估计性能，定位算法等方面时系统进行描述。文章基于两发一收的T^2／R无源相干定位系统。只利用多普勒频率信息时动目标进行状态估计，分析了系统的Cramer-Rao Bound（CRB）性能，并采用最大似然的估计算法对动目标进行定位。通过在数值单次与统计意义（Monte Carlo）上的仿真实验表明，利用多普勒频率信息的无源相干定位技术是可靠有效的。     

船舶航行辐射噪声的多普勒效应仿真

通过分析、比较已有水声信号多普勒频移仿真方法，针对船舶航行辐射噪声提出一种能够适应声源和接收者相对径向速度变化的、计算效率较高的水下宽带噪声信号多普勒效应仿真方法。仿真实验结果显示，该方法使船舶航行辐射噪声信号频域各分量的频率随着相对径向速度的变化呈现出不同的多普勒频移量，使得船舶航行辐射噪声信号的仿真达到了更高的逼真度。     

基于多普勒频率差的三站无源定位技术

如何消除无源时差定位系统对高重频目标源的定位模糊是一直倍受关注的问题。利用多普勒频率差无源定位算法解决了对高重频目标源的定位模糊问题,通过仿真实验验证了该方法的可行性和有效性。     

多普勒定位技术的研究

研究了一种多普勒定位技术，分析了多普勒测向的原理及利用测向过程中的相位信息进行测距的原理，提出了一种双信道补偿多普勒定位系统的方案。这是一种单站无源定位技术，具有多站定位无法比拟的优点，适合舰船对辐射源的快速定位。     

对机动目标的多站无源定位IMM算法

将交互式多模型（IMM）算法与集中式融合跟踪算法相结合,给出了集中式交互多模算法（CIMM）;基于目标的多普勒频率差和信号到达方向信息,利用CIMM算法对机动目标进行无源定位与跟踪,并与变维（VD）滤波算法的跟踪性能进行了比较.通过计算机仿真验证了CIMM算法是有效的,且该算法与VD算法相比定位精度更高、稳定性更好.     

雷电辐射源定位的时间反转方法与应用

将频域时间反转（time reversal，TR）聚焦技术应用于雷电辐射源探测定位，介绍了雷电辐射源探测系统的基本组成和TR定位算法，讨论了定位精度的影响因素，给出了典型应用实例.通过与传统的方法进行对比，发现该方法具有较好的鲁棒性，无需提取波形的到达时刻等信息，可直接利用检测波形的反向传播进行自动聚焦定位，并具有多辐射源同时定位的潜力.     

闪电声源定位系统研究

所研制的闪电声源定位系统由四元正方形麦克风声阵列、雷声信号传输系统和信号采集、记录与显示设备等部分组成.结合一次地闪雷声实测数据,采用广义互相关时延估计法计算了雷声信号到达不同麦克风的时间差,依据声光差定距法获得了声源点与麦克风阵列的距离,实现了雷电声源点的三维定位和闪电放电通道的三维重构.通过与同步观测到的雷电电磁脉冲场及大气电场进行对比,表明系统的定位效果较好.     

Parametric localization of distributed sources

Most array processing algorithms are based on the assumption that the signals are generated by point sources. This is a mathematical constraint that is not satisfied in many applications. In this paper, we consider situations where the sources are distributed in space with a parametric angular cross-correlation kernel. We propose an algorithm that estimates the parameters of this model using a generalization of the MUSIC algorithm. The method involves maximizing a cost function that depends on a matrix array manifold and the noise eigenvectors. We study two particular cases: coherent and incoherent spatial source distributions. The spatial correlation function for a uniformly distributed signal is derived. From this, we find the array gain and show that (in contrast to point sources) it does not increase linearly with the number of sources. We compare our method to the conventional (point source) MUSIC algorithm. The simulation studies show that the new method outperforms the MUSIC algorithm by reducing the estimation bias and the standard deviation for scenarios with distributed sources. It is also shown that the threshold signal-to-noise ratio required for resolving two closely spaced distributed sources is considerably smaller for the new method     

Principal-component localization of the sources of the backgroundEEG

A method, based on principal components for localizing the sources of the background EEG, is presented which overcomes the previous limitations of this approach. The spatiotemporal source model of the EEG is assumed to apply, and the method involves attempting to fit the spatial aspects of this general model with an optimal rotation of a subset of the principal components of a particular EEG. The method is shown to be equivalent to the subspace scanning method, a special case of the MUSIC algorithm, which enables multiple sources to be localized individually rather than all at once. The novel aspect of the new method is that it offers a way of selecting the relevant principal components for the localization problem. The relevant principal components are chosen by decomposing the EEG using spatial patterns common with a control EEG. These spatial patterns have the property that they account for maximally different proportions of the combined variances in the two EEG's. An example is given using a particular EEG from a neurologic patient. Components containing spike and sharp wave potentials are extracted, with respect to a standard EEG derived from 15 normal volunteers. Spike and sharp wave potentials are identified visually using the common spatial patterns decomposition and an EEG reconstructed from these components. Four dipole sources are fitted to the principal components of the reconstructed EEG and these source account for over 88% of the temporal variance present in that EEG     

红外辐射大气透过率影响因素的研究

大气传输是红外测温过程中不可忽视的一个重要问题。研究大气传输最主要的是计算大气透过率。在MODTRAN软件基础上,分析了8~12 μm波段多种关键因素对红外传输大气透过率的影响,研究了其变化规律。结果表明初始高度、边界层气溶胶、路径长度、波数间隔等对大气透过率都有一定的影响。其中路径长度对大气透过率的影响相对明显。通过外场测温实验,进一步研究路径长度对测温精度的影响,得出实际测温过程中的衰减率。比较分析仿真得到的大气透过率与实验测得的大气透过率二者之间的关系,拟合出二者的关系曲线。     

Burst of pulses in lightning electromagnetic radiation:observations and implications for lightning test standards

Bursts of regular microsecond-scale electric field pulses produced by three multiple-stroke cloud-to-ground discharges (a total of 2782 pulses) and by three cloud discharges (a total of 1436 pulses), all recorded within 20 km or so at the NASA Kennedy Space Center, are analyzed. The regular pulse bursts are similar in both cloud-to-ground and cloud discharges. A burst is characterized by some tens of pulses, each having a total width of a few microseconds, with an average interpulse interval of 6-7 μm. Pulse peaks in cloud-to-ground discharges are approximately two orders of magnitude smaller than return-stroke initial field peaks in the same flash. In both cloud and ground discharges, there is a tendency for the bursts to occur in the latter stages of a discharge, and positive and negative pulse polarities are about equally probable. Many bursts were found to be associated with the latter part of K changes while one pronounced M change appeared to be initiated by a regular pulse burst. The observed regular burst exhibit some similarity to the “multiple burst” (component H) of the standard lightning environment for the design and testing of aerospace vehicles. Overall, neither the present definition of the H component given in a previously published document (see Fed. Aviation Admin., US Dept. of Trans., advisory circular no. 20-136, Mar. 5, 1990) nor its newly proposed revision appears to be based on adequate experimental data     

Global optimization in the localization of neuromagnetic sources

The locations of active brain areas can be estimated from the magnetic field produced by the neural current sources. In many cases, the actual current distribution can be modeled with a set of stationary current dipoles with time-varying amplitudes. This work studies global optimization methods that find the minimum of the least-squares error function of the current dipole estimation problem. Three different global optimization methods were investigated: clustering method, simulated annealing, and genetic algorithms. In simulation studies, the genetic algorithm was the most effective method. The methods were also applied to analysis of actual measurement data     

The fine structure of positive lightning return-stroke radiation fields

The electric fields generated by lightning flashes striking the North Sea were measured, with a time resolution better than a few tens of nanoseconds, at Fano island in Denmark. The measuring station was located a few tens of meters away from the high water mark at the west coast of the island. This particular location made it possible to capture, with minimal propagation effects, the electromagnetic fields from lightning flashes striking the North Sea. The waveforms were recorded by a measuring system that could provide a time resolution of about 10 ns. The data recorded had the following features. The initial rising part of the positive return-stroke fields contains a slow front followed by a fast transition. The duration of the slow front of the positive return-stroke fields had an average of 8.3 /spl mu/s and its amplitude, measured as a fraction of the initial peak, had an average of 0.61. The 10%-90% rise time of the fast rising portion of the positive return-stroke fields was about 0.26 /spl mu/s, on average. The average peak value of the measured radiation fields normalized to 100 km was 15.7 V/m. The mean of the peak value of the time derivative of the radiation fields was 25 V/m//spl mu/s. The full width at half maximum of the radiation field derivative had a mean of 170 ns.