Benchmarking observational uncertainties for hydrology: rainfall,river discharge and water quality

This review and commentary sets out the need for authoritative and concise information on the expected error distributions and magnitudes in observational data. We discuss the necessary components of a benchmark of dominant data uncertainties and the recent developments in hydrology which increase the need for such guidance. We initiate the creation of a catalogue of accessible information on characteristics of data uncertainty for the key hydrological variables of rainfall, river discharge and water quality (suspended solids, phosphorus and nitrogen). This includes demonstration of how uncertainties can be quantified, summarizing current knowledge and the standard quantitative results available. In particular, synthesis of results from multiple studies allows conclusions to be drawn on factors which control the magnitude of data uncertainty and hence improves provision of prior guidance on those uncertainties. Rainfall uncertainties were found to be driven by spatial scale, whereas river discharge uncertainty was dominated by flow condition and gauging method. Water quality variables presented a more complex picture with many component errors. For all variables, it was easy to find examples where relative error magnitudes exceeded 40%. We consider how data uncertainties impact on the interpretation of catchment dynamics, model regionalization and model evaluation. In closing the review, we make recommendations for future research priorities in quantifying data uncertainty and highlight the need for an improved ‘culture of engagement’ with observational uncertainties. Copyright © 2012 John Wiley & Sons, Ltd.     

流场散度的误差估计

按照误差传递原理,推导出流场散度的误差估计式,并将其应用于赤道中东太平洋上升流区域水平散度误差的估计。应用结果表明:赤道中东太平洋上升流区多年平均流场的散度稳定,平均散度约为3.0×10-7s-1;和通常采用的误差估计公式相比,该估计公式降低了散度误差,从而提高了散度的可信度。     

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Probabilistic approach for active control of structures: experimental verification

In our previous study (Earthquake Engineering and Structural Dynamics 2003; 32 :2301), we have developed a probabilistic algorithm for active control of structures. In the probabilistic control algorithm, the control force is determined by the probability that the structural energy exceeds a specified target critical energy, and the direction of a control force is determined by the Lyapunov controller design method. In this paper, an experimental verification of the proposed probabilistic control algorithm is presented. A three‐story test structure equipped with an active mass driver (AMD) has been used. The effectiveness of the control algorithm has been examined by exciting the test structure using a sinusoidal signal, a scaled El Centro earthquake and a broadband Gaussian white noise; and, especially, experiments on control have been performed under different conditions to that of system identification in order to prove the stability and robustness of the proposed control algorithm. The experimental results indicate that the probabilistic control algorithm can achieve a significant response reduction under various types of ground excitations even when the modeling error exists. Copyright © 2004 John Wiley & Sons, Ltd.     

短潮位序列系统误差的探测及修复方法研究

提出了一种基于最小二乘潮位序列分段匹配方法。通过系统误差类型分析、分段段长确定、沉降发生具体时刻确定、系统误差类型探测和修复等算法研究,实现了临时潮位站潮位资料不同系统误差的准确探测和高精度修复。     

基于典型相关分析的变化检测中变化阈值的确定

以东营市为例 ,把基于典型相关分析的方法运用于多时相遥感影像的变化检测中。对于变化阈值的确定 ,采用了一种基于贝叶斯理论的最小错误率的方法。这种方法实质上是一种非监督分类的方法 ,即不需要地面实况数据或其它先验知识 ,直接对典型相关处理后的差值图像进行分析计算得到阈值 ,使变化检测的错误率达到最小。实验结果证明了这种方法的有效性。     

基于Matlab的GPS网间接平差教学设计与实现

GPS网间接平差是测绘类本科专业误差理论与测量平差基础教学的重要组成部分。本文针对GPS网间接平差存在的观测数据多、计算量大、在实际课堂教学中很难讲解清楚等问题,提出基于Matlab的GPS网间接平差教学设计与实现方法。给出GPS网间接平差课堂教学的内容及难点,阐述基于Matlab的GPS网间接平差程序设计流程及关键步骤的实现方法。结合3个具体的GPS网平差实例,展示程序运行的结果。结果表明,基于Matlab进行GPS网间接平差教学既有助于加深学生对GPS网间接平差理论知识的理解,培养学生理论联系实际的能力,又可以实现学生所学计算机高级编程语言与专业知识的有机结合,提高学生的编程能力和学习兴趣。     

南山26米射电望远镜轨道高差测量及其对指向精度的影响

轮轨式天线的轨道作为承载整个天线重量的基础,其精度直接影响天线在方位方向运转的平稳性,引起天线轴系偏差从而影响天线的指向精度。介绍改造后的乌鲁木齐南山26 m射电望远镜(Nanshan Radio Telescope, NSRT)轨道结构以及轨道高差测量,并建立天线在不同方位、俯仰角下轨道高差引起天线指向偏差的数学模型。利用"十字扫描"法实测多颗标准源在相应位置的指向数据,并通过高斯拟合得到指向偏差。通过分析可知,轨道高差引起的指向偏差经过修正可以提高天线的指向精度。     

GPS伪卫星的组合定位技术及其误差分析

介绍了GPS伪卫星组合定位的观测模型,详细论述了GPS伪卫星组合定位中存在的误差源,并对各误差源的消除方法进行了分析。     

利用数字中频信号模拟器和软件接收机对MBOC信号进行精度测试评估

在对MBOC信号的码跟踪噪声和多径误差进行理论分析的基础上,借助于所开发的数字中频信号模拟器和软件接收机进行了闭环测试评估。通过将数字中频闭环测试结果与理论预期值和模拟器仿真值进行对比分析,从多个层次有效验证了MBOC(6,1,1/11)相对于BOC(1,1)和BPSK-R(1)的测距精度改善。