隐射目标RCS缩比测量的数据处理及反演计算技术

本文介绍了一种利用模型测量结果来反演计算隐射目标原型ＲＣＳ的新技术，给出了反演数学方程、数据处理方法、反演计算方法以及部分测量和计算结果。经过比较，反演计算结果与实际测试曲线基本吻合，表明技术是可行的。     

基于Landsat数据的地表温度反演差异及参数分析

只有基于准确的地表温度反演算法计算出的产品数据,才能正确推广使用。研究基于Landsat-8、Landsat-9和气象站数据,对比了5种常用地表温度反演算法的结果,并对不同算法的反演结果和参数灵敏度进行了测试。结果表明：基于地表比辐射率参数计算的辐射传输方程和单通道算法反演结果与地面实测数据吻合较好。基于大气水汽参数计算的单窗算法和劈窗算法的反演结果均高于实测温度。基于平均温度参数计算的单窗算法反演精度误差较大。此外,比较了两种遥感数据在不同地物上反演温度的一致性。研究结果可为地表温度反演和产品选择提供参考。     

球面近场下相控阵天线口径诊断研究

在近场测量系统中,天线口径诊断是其中一项重要功能,它能够帮助天线设计师发现相控阵天线设计或者网络配置问题.平面近场中的口径诊断技术已经广泛地应用在雷达天线测试中,在球面近场测量中同样需要这种算法.本文基于球面坐标系下电磁场模式方法,得到球面近场条件下的口径反演算法.在仿真模型中计算得到了被测天线的口径场分布,计算结果与理论模型结果吻合.对X波段阵列天线进行了实际测试,得到了不同配置下的阵列天线口径反演结果,经过数据比对,证明了本文算法的幅度反演精度优于1 dB.     

米散射激光雷达降噪反演算法研究和应用

针对激光雷达信号中含有的噪声，提出一种将数据分区使用小波包变换分解和重构算法的信号降噪方法，该方法能为下一级消光系数反演提供高质量数据。为了验证该方法的有效性，比较雷达原始数据、小波包处理后反演的消光系数、分区小波包处理后反演的消光系数的差异，并进一步使用Bump、Block测试信号进行数值模拟，定量分析了分区小波包算法的去噪效果。分区小波包算法处理的Bump、Block测试信号评价函数的均方误差（MSE）和R值均优于一般小波包结果。结果表明，分区小波包降噪方法能通过降噪改善下一级反演消光系数结果，有效保护低空的激光雷达消光廓线的细节结构并抑制高空的信号噪声。空气气溶胶消光系数随时间和空间变化的伪彩图表明了所提方法的可行性和实用性。     

基于稀疏感应电流的微波实时成像方法

在医疗诊断、目标预警、无损探伤等诸多民用和军用领域中，非接触的实时微波成像技术具有重要研究意义。基于逆散射成像理论，非迭代的反演思路具备天然的实时计算能力，但其成像结果粗糙难以实用。为了提高反演图像质量，提出一种基于稀疏感应电流的实时微波成像方法。该方法利用稀疏先验信息和压缩感知算法求解成像区域中的感应电流，并结合传统非迭代反演框架实现实时成像。全波仿真结果和微波成像系统实验验证了所提方法的有效性。相比于传统非迭代反演结果，所提方法在成像质量和成像速度方面有显著提高，在实时监测、快速成像等场合具有重要应用潜力。     

微带线法测量微波材料的复介电常数

电磁波传输介质的电磁参数的准确测量,对材料的实际应用十分重要。研究微波材料介电常数的微带线测量方法,通过正演和反演过程的求解分析,对不同介电常数的材料进行了实际计算,同时还对测试误差进行了简要分析。结果表明,微带线测试微波材料的复介电常数方法可行,测量过程较为简单,测量结果准确。     

基于神经网络电性源半航空视电阻率反演研究

为解决目前电性源时域半航空视电阻率反演效率低、适用性差的问题,在快速计算电性源时域半航空感应电动势基础上,将理论计算的感应电动势进行等效变换,建立感应电动势与电阻率单一映射关系的样本集,选用三层误差反向算法(Back Propagation,BP)神经网络和Levenberg-Marquardt算法对样本集进行训练,优选出收敛速度快、误差小的网络参数.基于层状模型,对比了神经网络反演方法与传统方法反演效果,对于均匀 半空间模型,神经网络反演结果相对误差在5％以下,传统反演结果相对误差大于20％;对于层状大地模型,结果较传统方法更接近真实模型.基于神经网络的反演方法明显优于传统方法,这为半航空电磁数据提供了新的处理与解释方法.     

瑞利激光雷达探测大气温度算法分析

介绍了瑞利激光雷达的基本结构，描述了使用瑞利散射激光雷达探测平流层和中间层低部大气温度的数据处理方法，构建同时包含标准大气模式温度信息和实际探测背景噪声的模拟数据，对此模拟数据进行背景扣除、平滑去噪、参考点选取等计算分析，探讨提高温度反演精度的实用算法。并应用此数据处理方法对瑞利激光雷达的实际测量数据进行了计算处理，将计算结果与模式CIRJA86、HALOE卫星数据进行对比分析，反演高度30～45km时误差1—3K，45～65km误差大约在2—5K，65—70km误差〈10K。     

反常衍射近似在测量圆柱形粒子粒径分布中的应用

在光全散射法颗粒粒径测量中,基于米氏(Mie)理论的计算方法只能求出均匀球形粒子的消光系数,而且计算复杂。通过反常衍射近似(ADA)代替米消光系数,可以简化粒径分布的反演过程。对使用反常衍射近似方法计算圆柱形粒子消光系数的可行性以及限制条件进行深入的研究,并在非独立模式算法下,采用遗传算法反演粒径分布。仿真结果表明,当粒子的相对折射率在一定范围内时,利用反常衍射近似反演圆柱形粒子的粒径分布是完全可行的,反演结果稳定、可靠。对消光值测量结果加入3％相对误差时,反演误差为5．7％。该方法具有简单、直观、计算速度快等优点,适合颗粒粒径的在线测量。     

基于Hyperion数据的浅海水深直接反演方法研究

选用海南岛南部海区的EO-1 Hyperion高光谱遥感数据进行了浅海水深直接反演方法的研究。水深反演的关键问题是水体漫衰减系数的获取和海底底质的分类。通过主成分分析方法进行海底底部分类;应用QAA算法可以计算得到光学深水的漫衰减系数Kd,并对沿海光学浅水求Kd的方法提出了修正方法,最终代入基于辐射传递理论的直接反演方法中计算得到浅海水深。结果表明直接反演方法能够较快得到水深结果,且与海图能够匹配。     

Adaptive neural nets for generation of artificial earthquakeprecursors

A novel methodology for generation of artificial earthquake precursors was tested on Southern California earthquake data in reverse and real time modes. When it was tried as a real time generator of earthquake precursors, it successfully predicted the June, 1992, Landers earthquake. The methodology is based on the use of adaptive neural nets (ANN) that process a set of time-dependent attributes calculated in a moving time-window. The most important of them is a danger function. The structure of the neural net is defined by the properties of input data in the moving time window. Thus, the neural net continuously adapts its structure to the time variant properties of the input attributes. The main problem the authors encountered in training the neural net on the earthquake data was the small size of the training set compared to the number of parameters that describe the structure of the ANN. To prevent instability and over-fitting in the training session, the authors used a technique similar to the damping method in least squares approximation     

Robust minimum-distance estimation using the 3-parameter Weibulldistribution

Maximum-likelihood and minimum-distance estimates were compared for the three-parameter Weibull distribution. Six estimation techniques were developed by using combinations of maximum-likelihood and minimum-distance estimation. The minimum-distance estimates were made using both the Anderson-Darling and Cramer-Von Mises goodness-of-fit statistics. The estimators were tested by Monte Carlo simulation. For each set of parameters and sample size, 1000 data sets were generated and evaluated. Five evaluation criteria were calculated; they measured both the precision of estimating the population parameters and the discrepancy between the estimated and population Cdfs. The robustness of the estimation techniques was tested by fitting Weibull Cdfs to data from other distributions. Whether the data were Weibull or generated from other distributions, minimum-distance estimation using the Anderson-Darling goodness-of-fit statistic on the location parameter and maximum likelihood on the shape and scale parameters was the best or close to the best estimation technique     

基于统计检验的光电耦合器寿命预测模型研究

基于统计学思想,提出了寿命预测过程的逆向检验方法,通过Shapiro-Wilk检验验证试验数据的分布特性,通过方差齐性分析检验实验过程老化机理一致性,通过显著性检验对回归方程的显著性进行检验。文章将该方法应用于光电耦合器的寿命预测过程,通过提出的逆向检验方法验证后,所得预测结果与生产厂家提供的参考寿命接近。实验结果表明该方法能够有效地检验试验数据和评估模型的适用性,进一步提高光耦寿命预测的准确性,同时该方法对其他器件的寿命预测也具有一定的借鉴价值。     

一种评估旋转式机械设备工况的方法

用数据采集系统采集旋转式机械设备旋转构件上所选测点的振动位移，并计算出该振动参数基本统计特性的数值，就可以应用本文提出的判断不等式对设备的工况进行初步评估。动力增益因子的引入使静态测量精度能用于对振动动态过程的分析。以集成电路制造专用设备硅片磨床为例，阐述了这种评估方法。     

Procedure for determining diode parameters at very low forward voltage

A technique is proposed to extract the reverse saturation current parameter and ideality factor of semiconductor junctions from the low forward voltage region of the device’s characteristics. The method involves performing a mathematical operation on the experimental data that allows to calculate the parameters at values of forward current smaller than the reverse saturation current. The procedure was tested and its accuracy verified on synthetic I–V characteristics, with and without added simulated experimental error or noise. Good agreement is obtained between the parameters used in modeling and the extracted values. The procedure was also applied to experimentally measured I_B–V_BE characteristics of a real power BJT.     

An ultrasonic method for noninvasive estimation of vascular impedance to an absolute level: in vitro validation of the relationship between impedance and phase velocity

Vascular impedance is a quantity that characterizes the properties of the vascular bed. Assuming Newtonian fluid, laminar flow and linear system, impedance is related to phase velocity. The agreement between theoretical relationship and measured data is evaluated in an in vitro study. The setup consist of a computer-controlled flow generator, a variable fluid impedance and a measuring section. Phase velocity is calculated from multiple recorded vessel pulsations detected by ultrasonic pulse-echo technique. The reference impedance is calculated from simultaneously measured high-fidelity pressure and flow data. The impedance is analyzed in the range of 1-40 Hz with 1-Hz resolution. The evaluation of the noninvasive ultrasonic technique is focused on the resonance frequencies and the characteristic impedance. No significant difference (p > 0.05) is found in the resonance frequencies nor in the characteristic impedance. However, the impedance below 5 Hz is underestimated and the extension of the measuring section causes spatial averaging effects with reduced frequency resolution.     

Pattern shaping with hybrid mode corrugated horns

Hybrid modes in a square corrugated waveguide are investigated, and a technique of combining several modes for pattern shaping is described. The mode amplitudes are calculated from a known throat excitation and used to compute radiation patterns. One horn was designed, constructed, and tested. The theoretical patterns were in good agreement with experimental data.     

Performance improvement of 60‐GHz wireless optical systems with reverse‐parallel hybrid modulation scheme

This paper improves the performance of 60‐GHz wireless optical system including radio over fibre (RoF) and radio over free space optics (RoFSO), based on novel reverse‐parallel (RP) hybrid modulation scheme. This scheme combines the chromatic dispersion compensation technique of parallel modulation with energy efficiency manipulation technique of reverse modulation. Superior functioning of RoFSO is provided with reverse modulation compared with normal modulation. Comparative investigations are performed by loading 60‐GHz RF signal with 2.5 and 10‐Gbps data and modulating it with both reverse and hybrid modulators. Hybrid modulation performed better with improved BER of 10^?23 at distance of 51 km for 2.5‐Gbps data compared with reverse modulation with BER of 10^?7.     

The Influence of Model Parameters on BEG/MEG Single Dipole Source Estimation

This paper deals with source localization and strength estimation based on EEG and MEG data. It describes an estimation method (inverse procedure) which uses a four-spheres model of the head and a single current dipole. The dependency of the inverse solution on model parameters is investigated. It is found that sphere radii and conductivities influence especially the strength of the EEG equivalent dipole and not its location or direction. The influence on the equivalent dipole of the gradiometer is investigated. In general the MEG produces better location estimates than the EEG whereas the reverse is found for the component estimates. An inverse solution simultaneously based on EEG and MEG data appears slightly better than the average of separate EEG and MEG solutions. Variances of parameter estimators which can be calculated on the basis of a linear approximation of the model, were tested by Monte Carlo simulations.     

Domino logic with variable threshold voltage keeper

A variable threshold voltage keeper circuit technique is proposed for simultaneous power reduction and speed enhancement of domino logic circuits. The threshold voltage of a keeper transistor is dynamically modified during circuit operation to reduce contention current without sacrificing noise immunity. The variable threshold voltage keeper circuit technique enhances circuit evaluation speed by up to 60% while reducing power dissipation by 35% as compared to a standard domino (SD) logic circuit. The keeper size can be increased with the proposed technique while preserving the same delay or power characteristics as compared to a SD circuit. The proposed domino logic circuit technique offers 14% higher noise immunity as compared to a SD circuit with the same evaluation delay characteristics. Forward body biasing the keeper transistor is also proposed for improved noise immunity as compared to a SD circuit with the same keeper size. It is shown that by applying forward and reverse body biased keeper circuit techniques, the noise immunity and evaluation speed of domino logic circuits are simultaneously enhanced.