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在高动态导航中,卫星接收机自主完好性监测(RAIM)越来越受到重视。假如在单一模式下监测,RAIM系统至少需要接收到5颗卫星的信息才能监测出异常卫星,而如果需要辨识出故障卫星,则至少需要接收到6颗卫星的信息,这就使得单一的接收模式很难保证在全球范围内进行全天候的完整性检测。而随着北斗(BD)系统的迅速发展,使得采用GPS+BD导航模式进行监测成为可能。文中讨论了GPS和BD组合接收机中,在某时刻假设只有一颗卫星出现故障的情况下,怎样使用加权方法进行自主完好性监测。并通过仿真GPS、BD单模式和GPS+BD模式下的故障识别率和RAIM完好性可用率,证明了GPS+BD模式RAIM算法要优于任何一种单系统模式的RAIM算法。 相似文献
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故障检测是保证导航系统完好性的重要途径.针对接收机自主完好性监测算法RAIM需要至少5颗可见星时才能进行故障检测的问题,在惯性/卫星组合导航系统的框架下,通过构建能反映卫星故障特征的检验统计量,并根据检验统计量的分布确定相应的检测门限,提出了解分离和残差外推两种卫星故障检测方案.仿真结果表明:解分离算法能在存在RAIM漏洞时检测故障且易于进行系统重构,但其故障检测效率不高;残差外推法适用于检测慢变故障.仿真结果表明,改进方法故障检测效率有较大提高,甚至在只有三颗可见星时仍能较快地检测出慢变故障. 相似文献
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随着GPS等卫星导航技术的广泛应用,在实际导航中对接收机的导航定位精度,尤其对定位的有效性提出了越来越高的要求。目前对此较为有效的方法就是利用接收机自主完好性监视(RAIM, Receiver Autonomous Integrity Monitoring)进行保障,而且该方法日益凸显出其优越性,但目前对该方法的研究多基于单星故障的假设。随着新一代导航系统的完善以及组合导航技术的发展,双星甚至多星同时出现故障成为不可避免的话题。本文分析和比较了用于检测两颗卫星故障的偏差完好性风险(BIT, Bias Integrity Threat)法和保护限值(PL, Protection Level)法两种RAIM算法。通过数据仿真,对用不同方法检测卫星故障的可用性及故障检测率进行比较,并分析了两种方法存在差异的理论依据。通过分析比较,说明在未来接收机处理多颗卫星同时出现故障的情况时,如何更精确地描述统计检测量与定位偏差的关系以及如何处理不同测量噪声的影响是RAIM算法可用性及有效性的关键。 相似文献
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当接收机可以观测到的卫星数目增加时,多颗卫星同时出错的概率大大增加。传统的接收机自主完善性监测算法(Receiver Autonomous Integrity Monitoring,RAIM)通常用来检测并识别一颗故障卫星,在多颗卫星同时出错时的识别结果并不理想。提出了一种改进的RAIM算法,在奇偶矢量法的基础上,从找出无故障卫星出发,进一步用这些无故障卫星信息进行粗略定位,由接收机的粗略位置来计算各颗卫星的伪距偏差,从而识别出并剔除故障卫星。经仿真验证,该方法可以解决两颗故障卫星时奇偶矢量法中的故障偏差抵消问题。 相似文献
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当载体安装有GPS接收机和多个天线时,可以得到其姿态信息(航向角、俯仰角、横滚角);论述了利用载波相位姿态测量的解析法,利用了基线长固定的条件,在整周模糊度初始化时进行粗搜索,利用模糊度函数法进行判断筛选整周模糊度组合,减少了搜索空间;接收机自主完好性监测(RAIM)的概念被引入到姿态测量算法中,有效地剔除问题卫星,改善AFM算法;系统姿态测量结果达0.1标准差,故障卫星可由RAIM检测并剔除;结果表明RAIM算法能有效提高姿态测量结果可靠性。 相似文献
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随着GNSS-R技术的迅速发展和应用领域的增多,对GNSS-R的多卫星系统的研究显得尤为重要,目前GPS单系统得到了很好的应用,但是GPS单系统不能满足GNSS-R的应用领域,在此发展的趋势下本设计对GPS/BD双系统进行了探索.GNSS-R反演的应用需要导航定位信息提供探测区域接收平台和卫星的详细信息.主要设计完成了GPS/BD双系统定位数据处理软件,包括GPS/BD双系统定位信息的快速接收和数据的正确提取及显示;利用串口通信实现信息的接收及控制命令的发送;可见星星座图显示、状态监控窗口显示和卫星跟踪信息显示等功能;并根据定位数据进行镜面反射点的计算.经过实际工程项目的测试,本软件具有较好的实时性和实用性. 相似文献
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European Community policy and the market 总被引:1,自引:0,他引:1
C. Lloyd 《Journal of Computer Assisted Learning》1993,9(2):86-91
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. 相似文献
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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。 相似文献
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David Poole 《Computational Intelligence》1989,5(2):97-110
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. 相似文献
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Watts S. Humphrey 《Annals of Software Engineering》2002,14(1-4):39-72
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. 相似文献
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基于复小波噪声方差显著修正的SAR图像去噪 总被引:4,自引:1,他引:3
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。 相似文献
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R. NOSS 《Journal of Computer Assisted Learning》1987,3(1):2-12
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. 相似文献
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C. Xiang 《控制理论与应用(英文版)》2014,12(3):217-217
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 相似文献
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《浙江大学学报:C卷英文版》2014,(7)
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. 相似文献
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Alan V. Di Vittorio 《Remote sensing of environment》2009,113(9):1948-2750
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. 相似文献
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Philip Marks 《Cryptologia》2018,42(1):1-80
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). 相似文献