单球无味卡尔曼滤波在飞船姿态估计中的应用

提出了一种用矢量观测来估计飞船姿态的单球无味卡尔曼滤波算法.该算法将单球无味变换与无味卡尔曼滤波结合起来,与采用尺度无味变换的无味卡尔曼滤波相比,具有更低的计算量.飞船的姿态运动学描述采用了四元数,而用广义罗德里格斯参数来克服卡尔曼滤波过程中的四元数归一化误差.仿真结果表明,该算法比标准扩展卡尔曼滤波具有更低的姿态估计误差及更快的收敛率.与无味卡尔曼滤波相比,较低的计算量及相同的估计精度使该算法更适合在实时姿态估计中应用.     

基于修正的卡尔曼滤波的姿态估计算法研究

研究惯导系统的稳定性问题,其中微惯性测量单元(MIMU)可以为捷联惯导系统提供实时的姿态和航向信息。研究姿态估计提高导航精度,由于陀螺漂移引起姿态误差,单独使用MIMU使姿态精度差。为了克服陀螺误差随时间积累不断增大,无法长时间提供稳定的姿态的缺点,提出采用磁强计修正的卡尔曼滤波四元数姿态估计算法。算法以姿态四元数为状态向量,通过四元数更新方程建立离散滤波状态方程,将加速度计和磁强计输出的六维数据转化为四元数的量测值建立量测方程,有效减少了计算量,补偿陀螺的漂移误差带来的影响。仿真结果表明改进算法提高了捷联惯导系统的精度和稳定性。     

自主姿态测量算法研究

航姿系统一般不实时计算速度和位置信息,无法补偿地球自转和表观运动引起的分量误差,同时陀螺漂移较大,载体长时间持续机动时,出现姿态精度不高,甚至发散的问题。提出了一种基于卡尔曼滤波的姿态融合算法,将等效陀螺漂移列入系统状态,利用卡尔曼滤波的新息对运动状态进行判别,在一定条件下,用加速度计的输出作为量测量进行卡尔曼滤波的量测更新过程。实验结果表明,所提出的姿态融合算法考虑了陀螺漂移,能提高载体长时间机动时的姿态精度。     

基于四元数姿态估计的捷联惯导初始对准算法

针对传统动基座捷联惯导系统OBA粗对准算法,在低精度传感器中,易受到陀螺零偏的影响,存在累计误差导致观测矢量精度低的缺点,本文研究了基于四元数的无迹卡尔曼滤波来进行载体的姿态估计.该方法可以估计陀螺仪的零偏,并在预测方程中将其去除,能够有效地抑制陀螺零偏带来的累计误差,从而提高姿态误差角的收敛精度.最后设计了仿真与车载实验,验证本文所研究算法的有效性.     

基于DSC与MEMS的微型测姿系统研究

针对当前无人机航姿系统对GPS信息依赖严重的特点,设计了基于MEMS ADIS16405传感器和数字信号处理器（DSC）TMS320F28335的微型惯性测姿系统。以MEMS传感器的角速度、重力加速度、航向信息,建立姿态四元数方程,解算出飞行器姿态。运用扩展卡尔曼滤波方法,消除MEMS陀螺漂移误差。DSC28335的硬件平台实现了四元数扩展卡尔曼滤波算法。转台仿真试验表明,漂移误差能在线最优估计和实时补偿,输出的航姿精度较高。该微型测姿系统具有较高的实用价值。     

自由转子陀螺的漂移误差模型识别系统

本文介绍了一个自由转子陀螺的漂移误差模型识别系统.该系统在实现数据采集的基础上采用扩展卡尔曼滤波算法进行模型参数的识别,在扩展卡尔曼滤波计算中采用了改进的格雷姆--斯密特算法(MGS)进行协方差矩阵的计算,并使用卡尔森算法(CLS)进行状态修正和协方差修正.系统通过了实际的试验验证.试验结果表明该模型识别系统具有足够的精度,完全可以满足自由由转子陀螺漂移误差模型辨识的要求.     

基于卡尔曼滤波器的航姿系统测姿算法研究

航姿系统通常没有载体位置信息和速度信息的解算,且陀螺漂移较大,存在着载体持续机动时姿态精度不高,甚至消失的问题,因此通常的导航算法已不再适用.设计了一种基于卡尔曼滤波技术的姿态算法,用重力加速度在机体系的分量gb和陀螺漂移作为待估计的状态量,进行卡尔曼滤波的时间更新过程,利用加速度计的输出在一定条件下作为观测量,进行卡...     

用四元数状态切换无迹卡尔曼滤波器估计的飞行器姿态

在较大初始姿态误差角下, 针对捷联惯导/CCD星敏感器(strap-intertial navigation system/CCD star sensor, SINS/CCD)姿态估计系统扩展卡尔曼滤波(extended Kalman filter, EKF)算法精度下降的问题, 提出了基于四元数的状态切换无迹卡尔曼滤波算法. 通过状态实时切换降低了全维无迹卡尔曼滤波(unscented Kalman filter, UKF)的维数, 减小了计算复杂度, 提高了系统的实时性. 文中采用基于特征向量求解的代价函数法计算四元数均值避免了UKF算法中四元数规范化的限制; 利用乘性误差四元数表示姿态更新点与估计点之间的距离, 解决了四元数协方差阵奇异性问题. 仿真实验结果表明: 与EKF相比, 该算法在精度上有较大提高; 与全维UKF算法和修正罗德里格斯参数UKF算法相比, 该算法精度相当但估计时间均有不同程度的减少.     

基于间接EKF的MEMS惯性系统最优姿态估计

针对MEMS惯性系统姿态估计中的扩展卡尔曼滤波EKF(Extended Kalman Filter)是非线性状态方程的次优估计且性能受量测噪声协方差矩阵影响的问题,提出一种间接EKF最优姿态估计方法。推导与状态向量扰动相关的线运动特性并设计扰动状态方程,采用标准线性卡尔曼滤波完成扰动状态及其协方差最优更新,最后利用加速度计输出作观测量并采取链式法则完成量测矩阵的求取。对比实验结果表明,间接EKF算法可有效降低陀螺随机漂移对姿态估计的影响,姿态收敛速度与精度均优于传统EKF方法。     

小型尾坐式飞行器自适应SRUKF姿态算法

针对小型尾坐式飞行器姿态估计问题,设计了由陀螺、加速度计、磁强计组成的姿态测量系统。为了抑制MEMS陀螺漂移导致的姿态误差,以四元数为状态变量,以加速度计和磁强计的输出作为观测变量,建立了滤波模型。采用平方根无迹卡尔曼滤波(SRUKF)对传感器信息进行融合,保证了滤波算法的数值稳定性。由于小型尾坐式飞行器抗干扰能力弱,引入自适应算法,解决了量测信息受到干扰时滤波精度下降的问题,提高了系统的鲁棒性和可靠性。仿真结果表明,存在外界磁场干扰时,姿态误差小于1°。通过实际飞行实验,验证了算法的可行性。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).