基于加权TV正则化的X射线CT系统能谱估计方法

在CT硬化伪影校正、双能CT图像重建以及CT辐射剂量计算等实际应用中,X射线的能谱信息具有重要的作用。然而,由于透射测量方程组系数矩阵的病态性、X光子的统计涨落和噪声的干扰,使得EM等能谱估计方法难以获得较精细的能谱刻画。针对该问题,提出一种基于加权TV正则化的X射线CT系统能谱估计方法。首先采用能谱能量范围内带有不同K-edge的材料作为体模以降低投影测量方程之间的相关性。然后,利用CT成像系统的几何参数来获取投影测量数据所对应的准确透射长度信息来减小投影方程的测量误差。最后,综合利用透射衰减测量数据的保真性、轫致辐射能谱部分的连续性、特征辐射能谱部分的离散性、能谱的非负性和归一性以及平均有效衰减系数等信息,使用加权TV正则化方法建立目标函数,利用正则化理论中的L曲线准则通过黄金分割参数搜索策略求得最优正则化参数及对应的能谱估计结果。分别通过不同统计波动模型下的仿真能谱和实际测量数据对算法性能进行了验证,结果表明该方法与EM等方法相比,不受初始能谱的影响,有效提高了能谱估计结果的稳定性和准确性。     

矢量水听器垂直阵列数据融合高分辨方位估计算法

为了实现矢量水听器垂直阵列对目标的高分辨方位估计,提出了基于MUSIC子频带最优加权数据融合方法。该方法采用MUSIC算法对划分的各窄带信号进行方位估计,并在各子频带对多基元方位估计结果进行最优加权最小二乘融合处理,最后通过加权直方图统计法得到最终方位估计结果。对算法进行的仿真及海上试验数据处理结果表明:本文算法在方位估计精度、方位估计正确概率、多目标分辨以及对噪声子频带的抑制能力方面都优于单个基元MUSIC以及多基元复声强器融合算法。      

矢量水听器垂直阵列数据融合高分辨方位估计算法

为了实现矢量水听器垂直阵列对目标的高分辨方位估计,提出了基于MUSIC子频带最优加权数据融合方法。该方法采用MUSIC算法对划分的各窄带信号进行方位估计,并在各子频带对多基元方位估计结果进行最优加权最小二乘融合处理,最后通过加权直方图统计法得到最终方位估计结果。对算法进行的仿真及海上试验数据处理结果表明:本文算法在方位估计精度、方位估计正确概率、多目标分辨以及对噪声子频带的抑制能力方面都优于单个基元MUSIC以及多基元复声强器融合算法。     

相机位姿估计的加权正交迭代算法

在相机位姿估计的实际应用中,参考点的坐标数据不可避免地包含了测量误差,其量值大小通常不会完全一致,如果不区别测量误差直接进行相机位姿估计,将可能导致估计结果与真值相差甚远。为此,在广泛应用的正交迭代算法基础上,提出了相机位姿估计的加权正交迭代算法,该方法以加权共线误差为目标函数,根据像面重投影误差确定权重系数取值,优化相机位姿估计结果,具有精度高、稳健性好等优点,且满足全局收敛条件。数值仿真实验与风洞迎角实验的结果表明,本文算法更加有效,能够抑制不同程度测量误差对相机位姿估计结果的影响,所得结果明显优于正交迭代算法,具有较强的工程实用价值。     

水声通信系统中双向turbo均衡算法

提出了一种水声通信系统中直接自适应双向turbo均衡算法。摒弃了信道估计步骤,采用基于直接自适应的turbo均衡器,并利用内嵌数字锁相环的判决反馈均衡器结构跟踪时变信道,采用最速优化算法自适应调整迭代步长,使得收敛速度和算法性能得到很好折中。此外,利用最小均方误差准则,得到最优权重因子,对正向与反向turbo均衡结果加权求和,消除误差传播效应。仿真和湖上实验验证了方法的正确性,双向均衡的性能优于单向均衡。湖上实验结果表明,基于直接自适应算法相比于基于信道估计的算法,对时变信道不敏感,能获得更低的误比特率。      

二次加权频域自适应时延估计算法与应用

时延估计问题在许多工程应用中具有重要的意义。本文提出了一种二次加权频域自适应时延估计模型,给出了二次加权频域SCOT和ML自适应时延估计算法,推导了二次加权频域SCOT自适应时延估计的方差。把该算法应用于对武装直升机的声测无源定位中,用实测直升机噪声数据进行了计算机仿真。结果表明,在低信噪比情况下,二次加权频域自适应时延估计具有更好的时延估计性能。     

基于加权最小二乘估计的双基地声呐定位算法研究

依据T/R-R型双基地声呐的工作特点,提出了基于加权最小二乘(WLS)估计的双基地声呐定位算法,通过数值仿真,研究了不同基线长度下该算法的定位精度,给出了WLS算法定位精度的几何分布。结果表明,运用该算法对水下目标进行定位,比单纯基于波达时间(TOL)的定位方法,双基地系统可以获得更高的定位精度。     

一种星敏感器主点和焦距的加权在轨标定方法

星敏感器作为卫星姿态测量装置,其在轨服役过程中,主点和焦距的标定精度是影响其姿态输出精度的主要因素。针对标定过程中含有随机测量噪声偏大的星像点,导致星敏感器主点和焦距的标定结果产生较大偏差的问题,提出了一种星敏感器主点和焦距的加权在轨标定方法。该方法首先建立了星敏感器在轨标定模型,然后引入合理的标定权值,加入到最小二乘估计主点和焦距的过程中,寻找并剔除随机测量噪声偏大的星点,最后将加权估计出的结果作为测量,采用扩展卡尔曼滤波对星图进行处理。仿真结果表明,在星点位置存在较大误差的情况下,该方法能剔除随机测量噪声偏大的坏点。星内角距统计偏差约为传统方法的1/10,与真值相比标定参数精度分别为0.219 9像素、0.148 7像素、3.38 μm。     

一种恒定束宽波束形成矩阵的加权正交化方法

提出了一种加权正交化恒定束宽波束形成矩阵。对正交后不同频率分量对应的波束形成矩阵进行不同程度的加权,可以得到无畸变的波束输出信号,保证检测能力;并且当信号源具有均匀谱的情况下,可以实现波束形成前后无能量损失,获得高的方位估计性能。计算机仿真和水池实验数据分析证实了加权正交化方法可同时获得高的检测性能和方位估计性能。     

MPSK调制系统中的自适应信道估计

本文研究了在MPSK调制方式下,不发送训练序列的直接判决自适应信道估计问题。为提高信道估计性能,提出采用软判决鉴相估值来调整加权最小均方（WLMS）和加权递归最小二乘（WRLS）自适应算法中的权值来进行信道估计,并研究了改进的软判决WRLS算法。结果表明,软判决加权LMS算法比一般LMs性能有很大提高,改进的软判决WRLS算法估计性能优于加权RLS算法。     

A differentially weighted Monte Carlo method for two-component coagulation

The direct simulation Monte Carlo (DSMC) method for population balance modeling is capable of retaining the history of each simulation particle and is thus able to deal with multivariate properties in a simple and straightforward manner. As opposed to conventional DSMC approaches that track equally weighted simulation particles, a differentially weighted Monte Carlo method is extended to simulate two-component coagulation processes and is thereby able to simulate the micromixing of the components. A new feature of the method for this bivariate population balance modeling is that it is possible to specify how the simulation particles are distributed over the compositional axis. This allows us to obtain information about particles in those regions of the size and composition distribution functions where the non-weighted MC methods place insufficient simulation particles to obtain an inaccurate solution. The new feature results in lower statistical noise for simulating two-component coagulation, which is validated by using two-component coagulation cases for which analytical solutions exist (a discrete process with sum kernel for initial monodisperse populations and a process with constant kernel for initial polydisperse populations).     

Graphical models for statistical inference and data assimilation

In data assimilation for a system which evolves in time, one combines past and current observations with a model of the dynamics of the system, in order to improve the simulation of the system as well as any future predictions about it. From a statistical point of view, this process can be regarded as estimating many random variables which are related both spatially and temporally: given observations of some of these variables, typically corresponding to times past, we require estimates of several others, typically corresponding to future times.

Graphical models have emerged as an effective formalism for assisting in these types of inference tasks, particularly for large numbers of random variables. Graphical models provide a means of representing dependency structure among the variables, and can provide both intuition and efficiency in estimation and other inference computations. We provide an overview and introduction to graphical models, and describe how they can be used to represent statistical dependency and how the resulting structure can be used to organize computation. The relation between statistical inference using graphical models and optimal sequential estimation algorithms such as Kalman filtering is discussed. We then give several additional examples of how graphical models can be applied to climate dynamics, specifically estimation using multi-resolution models of large-scale data sets such as satellite imagery, and learning hidden Markov models to capture rainfall patterns in space and time.     

Dual-ring 16-Star QAM direct and coherent detection in 100 Gb/s optically amplified fiber transmission: simulation

This paper presents the transmission performances, by simulation, of optical communication systems over 10 spans of dispersion compensated and optically amplified fiber distance with a bit rate of 100 Gb/s, by employing modulation formats of two amplitude levels and 8 phase states per amplitude level, the 2R-16-Star QAM constellation under direct and coherent detection with and without phase estimation. Different ring ratios of the amplitude levels are examined and associate transmission performances are reported. Optical signal to noise ratio is achieved with 18 dB and 23 dB for back to back and long haul transmission cases with a dispersion tolerance of  ±67 ps/nm at 2 dB power penalty of the eye opening at 100 Gb/s. Monte–Carlo simulation is also performed and a receiver sensitivity of  − 15 dBm is achieved for a BER of 10⁻⁵under direct detection after 1100 km of dispersion-compensated and optically amplified transmission. Transmission performances, bit error rate versus receiver sensitivity, are also confirmed with the use of the eye diagram and associate multiple-peaks statistical spectral density distribution. For 100 Gb/s 2R-16-Star QAM coherent transmission, an improvement of the receiver sensitivity of 2.5 dB and 3.5 dB is obtained for coherent detection without phase estimation and respectively. Under coherent detection with phase estimation, the chromatic dispersion tolerance reaches  ±100 ps/nm for a 2 dB eye opening penalty at 100 Gb/s bit rate. Comparative studies of the transmission performances of the Star and Square QAM modulation formats are also conducted under the fiber linear and nonlinear effects and detection with and without phase estimation.     

基于视觉感知的光谱评估尺度

光谱颜色复现和色度精度是评价光谱重建算法准确的基础。简单而直观的评价指标对颜色复现控制是必不可少。该指标需要同时表征复现颜色的光谱差和色度差。在研究光谱匹配评估的方法基础上,提出基于颜色视觉感知的三种光谱评估指标,通过加权人眼视觉匹配函数,实现颜色光谱差与色度的评估。通过孟塞尔颜色系统的光谱数据,该论文分析与验证三种视觉加权的评估指标的有效性。通过孟塞尔颜色系统数据,这些指标在CIELab均匀色空间中分布均匀而稳定,从而证明加权算法的评估指标是既表征到颜色感知又反映出颜色的光谱相似度。实证结果表明,加权的指标可以实现同时表征实际人眼的颜色感知和颜色光谱差异。基于人眼视觉感知的评估指标解决了颜色的原始光谱和重建光谱的光谱匹配精度的定量评价问题。所提出评价指标通过一个简单而直观的数值实现对复现颜色光谱与色度评估。     

直接模拟法和统计估计法研究平面波通过离散随机介质的散射

本文从输运理论出发,利用逐项积分法获得直接模拟法和统计估计法的估计函数。研究了平面波通过平面离散随机介质的透射光强和反射光强随光学厚度、反照率、不对称因子的变化。统计估计法获得与文献[2]给出数据完全一致的结果。在直接模拟法中由于粒子空间位置抽样产生较大的统计涨落,当光学厚度增大,散射的各向异性增强及强吸收时其结果的偏差增大。 关键词：     

Simultaneous estimation of unwrapped phase and phase derivative from a closed fringe pattern

We propose a new approach for the direct estimation of the unwrapped phase from a single closed fringe pattern. The fringe analysis is performed along a given row/column at a time by approximating the phase with a weighted linear combination of linearly independent basis functions. Gaussian radial basis functions with equally distributed centers and a fixed variance are considered for the phase approximation. A state space model is defined with the weights of the basis functions as the state vector elements. Extended Kalman filter is effectively utilized for the accurate state estimation. A fringe density estimation based criteria is established to select whether the phase estimation is performed in a row by row or column by column manner. In the seed row/column decided based on this criteria, the optimal basis dimension is computed. The proposed method effectively renders itself in the simultaneous estimation of the phase and the phase derivative. The proposed phase modeling approach also allows us to successfully demodulate the low density fringe patterns. Simulation and experimental results validate the practical applicability of the proposed method.     

基于X射线脉冲星导航的模拟调制仿真源研究

为实现X射线脉冲星导航系统在地面的演示验证, 提出并设计了一种高精度X射线脉冲星仿真源. 该仿真源由模拟调制信号发生器和栅控X射线球管组成. 模拟调制信号发生器根据脉冲星标准脉冲轮廓数据和栅控球管特性曲线, 利用直接数字频率合成技术产生模拟调制信号, 加载在X射线球管控制栅极, 从而控制轰击阳极靶的高速电子数目来实现X射线的调制, 产生与脉冲星标准脉冲轮廓高吻合度的X射线光子统计分布. 在X射线脉冲星地面仿真系统中对Crab脉冲星仿真源的性能进行测试, 测试结果为: 采集脉冲轮廓与标准脉冲轮廓时域相关度和频率相关度分别达到0.9774和0.9853, 辐射流量为1. 90 ph·cm^-2·s^-1, 脉冲辐射流量与总辐射流量之比为76.15%, 脉冲半宽度为1.879 ms. 结果表明: 该仿真源具有符合度高, 成本低, 操作简单灵活, 对X 射线脉冲星导航关键技术的攻关具有重要的意义. 关键词： X射线脉冲星导航 仿真源 栅控X射线球管 直接数字频率合成