Variogram Model Selection via Nonparametric Derivative Estimation

Before optimal linear prediction can be performed on spatial data sets, the variogram is usually estimated at various lags and a parametric model is fitted to those estimates. Apart from possible a priori knowledge about the process and the user's subjectivity, there is no standard methodology for choosing among valid variogram models like the spherical or the exponential ones. This paper discusses the nonparametric estimation of the variogram and its derivative, based on the spectral representation of positive definite functions. The use of the estimated derivative to help choose among valid parametric variogram models is presented. Once a model is selected, its parameters can be estimated—for example, by generalized least squares. A small simulation study is performed that demonstrates the usefulness of estimating the derivative to help model selection and illustrates the issue of aliasing. MATLAB software for nonparametric variogram derivative estimation is available at http://www-math.mit.edu/~gorsich/derivative.html. An application to the Walker Lake data set is also presented.     

利用大地水准面模型计算垂线偏差的方法及精度分析

根据大地水准面与垂线偏差的关系,设计合理的计算方案,给出利用大地水准面模型计算垂线偏差的简化公式,并通过模拟计算探讨大地水准面相对精度、取点间距和已知点选取及个数对计算结果的影响。利用GEOID12B模型分别计算GSVS2011、GSVS2014项目中各测站点和美国西部区域（40°~45°N,100°~105°W,分辨率为1′）的垂线偏差,并与GSVS项目垂线偏差实测值和DEFLEC12B模型值进行比较。结果表明,垂线偏差南北分量和东西分量的计算精度均优于±0.5″,说明利用相对精度为cm甚至亚cm级的大地水准面模型可获取较高精度的垂线偏差。     

A Note on Tsunami Bore Front

A note is presented on tsunami bore front. This tsunami bore front is an old dynamical problem but also a new problem to be understood. The tsunami event on 2004 December 26 has raised this is an urgent problem. The author introduces here a model in order to see a hydrodynamical specific property of the tsunami bore front. This modeling gives us a new understanding about what mechanics is for the interested tsunami bore front, especially, around a coastal zone. This work adds a new understanding about mechanics of water motions as the tsunamis generated by the earthquake undersea at a distant area from the coast. The model in this work points out a specific transitional pattern as a function of time and space of tsunami bore front. This modeling gives what is essential at considering tsunami bore front.     

象山皇城海滩稳定性分析与防护对策

以浙江岬湾砂质海岸象山皇城海滩为例,运用抛物线模型,分析得出皇城海滩的冲淤演化动态,并通过历史岸线形态对比探讨皇城海塘对其的影响,最终提出防止海岸侵蚀的对策。研究结果表明,皇城海滩北部有一定的侵蚀,其平面形态还未达到静态平衡,处于不稳定状态;皇城海滩北段海塘修建得过于靠海,致使海滩最重要的泥沙补给源——后滨沙丘被阻断,甚至消失,同时大潮水位可直接淹没海塘堤脚,加上海塘前为近破波,滩面水流和泥沙运动剧烈,最终导致堤前滩面的冲刷。基于此,防止海岸侵蚀的最佳对策是在拆除、重建海滩北部部分海塘后再进行适当的海滩养护。通过对皇城海滩的稳定性研究,了解海塘建设的影响,可为浙江岬湾海滩资源的合理开发、海岸防护工程建设提供一定的科学依据。     

Numerical Simulation of Wind and Temperature Fields over Beijing Area in Summer

1. IntroductionThe basic role of urban-rural boundary layer re-search is to study all kinds of physical process changesin the atmosphere boundary layer over urban and itssurrounding areas. Urban heat island (UHI) is a well-known feature of urban-rural climate. Attempts toincrease the understanding of the causes of the UHIand other urban-rural boundary layer phenomena haveused observational, theoretical and modelling methodssince long before. Seaman (1989) used a hydrostaticmodel, with real …     

山东东营凹陷东部浊积扇油藏成藏条件与模式

岩性油气藏已成为东营凹陷油气勘探重点。东营凹陷东部在沙三、沙四段沉积时期发育了大量厚层烃源岩, 为圈闭成藏提供了充足的油气资源。勘探证实, 东营凹陷东部发育三角洲前缘滑塌浊积、深水浊积扇等砂体类型, 同时发育断裂型、砂体型、不整合面型等多种输导体系和良好的泥岩盖层。生、储、盖条件在时间、空间上具有良好的组合关系, 为形成砂岩透镜体岩性油气藏和构造-岩性油气藏提供了良好条件。      

一种导航卫星中长期轨道预报方法

基于神经网络混合建模的思想提出一种针对导航卫星的中长期轨道预报方法,在原动力学模型的基础上引入神经网络模型作为补偿,从而获得新的预报模型。在训练过程中神经网络通过学习动力学模型轨道预报误差来掌握其变化规律,并在预报过程中为动力学模型预报提供补偿,以提高预报精度。对GPS卫星动力学模型中长期预报误差的特点进行分析,然后根据所得结论提出混合模型的中长期(15 d以上)预报方案,最后通过对GPS卫星的仿真试验证明混合模型的改进效果,结果表明新方法在15~40 d的预报上表现出很好的改进效果。     

三峡水库调节典型时段对鄱阳湖湿地水情特征的影响

三峡工程建成运行将改变下游的水文过程,影响通江湖泊湿地生态系统.本文选取水文情势变化大且可能对植被乍长产生较大影响的汛末蓄水和汛前腾空两个时段,运用长江中游江湖耦合水动力模型计算了三峡水库不同凋节流量下湖泊水位变化特征,并结合湖泊高程和面积关系曲线,分析了不同增减下泄流量对洲滩湿地淹没出露的影响.结果表明,三峡水库汛末...     

山区县域可持续发展定量研究

在充分认识山区县域特征的基础上,依据可持续发展思想,建立了评价山区县域可持续发展的指标体系和定量评价模型。将其应用于交口县,获得了较满意的效果。     

利用自回归模型检测地球极移重力效应

同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数，研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度，结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近，叠积后实际重力观测与极移重力信号理论值之间的差异分别为0．4％和3．9％，说明超导重力仪可有效监测极移导致的重力变化。