Changes in Correlation Coefficients with Spatial Scale and Implications for Water Resources and Vulnerability Data     

Shama Perveen  L. Allan James 《The Professional geographer》2013,65(3):389-400

Previous studies of correlation coefficients between paired observations using census, hydrologic, and remote sensing data abound. It is well established that bivariate relationships at coarser spatial resolutions are often stronger than at finer resolutions. No assessment as yet, however, corroborates this tendency with water resources variables. In this study, multiscale correlations between water use or water availability and population are presented in three river basins—the Missouri (United States), Danube (Europe), and Ganges (South Asia). High-resolution gridded data sets were obtained at 0.5° and resampled to fourteen different geographic scales to examine the effects of scale on the strength and trends of correlations. Correlation coefficients between most variable pairs increased at coarser scales. Smoothing fine-scale spatial patterns in the data at coarser scales is posited as a possible explanation. The increase was not often linear, however, nor was there always an increase. The Missouri Basin did not show a significant increase in correlations between water use and population with grid-cell size and nonlinear increases are evident in the Ganges Basin.  相似文献   

Monitoring Growth in Rapidly Urbanizing Areas Using Remotely Sensed Data     

《The Professional geographer》2013,65(3):371-386

Urbanization and the ability to manage for a sustainable future present numerous challenges for geographers and planners in metropolitan regions. Remotely sensed data are inherently suited to provide information on urban land cover characteristics, and their change over time, at various spatial and temporal scales. Data models for establishing the range of urban land cover types and their biophysical composition (vegetation, soil, and impervious surfaces) are integrated to provide a hierarchical approach to classifying land cover within urban environments. These data also provide an essential component for current simulation models of urban growth patterns, as both calibration and validation data. The first stages of the approach have been applied to examine urban growth between 1988 and 1995 for a rapidly developing area in southeast Queensland, Australia. Landsat Thematic Mapper image data provided accurate (83% adjusted overall accuracy) classification of broad land cover types and their change over time. The combination of commonly available remotely sensed data, image processing methods, and emerging urban growth models highlights an important application for current and next generation moderate spatial resolution image data in studies of urban environments.  相似文献   

Roughness scale dependence of the relationship between tracer longitudinal dispersion and Peclet number in variable‐aperture fractures          下载免费PDF全文

Zhi Dou  Zhifang Zhou  Jinguo Wang  Yong Huang 《水文研究》2018,32(10):1461-1475

The relationship between the longitudinal dispersion (D_L) and Peclet number (Pe) is crucial for predicting and simulating tracer through the variable‐aperture fracture. In this study, the roughness of the self‐affine fracture wall was decomposed into primary roughness (relatively large‐scale waviness) and secondary roughness (relatively small‐scale waviness) by a multiscaled wavelet analysis technique. Based on the complete dispersion mechanism (diffusion, macrodispersion, and Taylor dispersion) in the variable‐aperture fracture, three relationships (second‐order, power‐law, and linear relationships) between the D_L and Pe were investigated at large and small scales, respectively. Our results showed that the primary roughness mostly controlled the Taylor dispersion mechanism, whereas the secondary roughness was a dominant factor for the macrodispersion mechanism. Increasing the Hurst exponent and removing the secondary roughness led to the decreasing range of Pe where macrodispersion mechanism dominated the solute transport. It was found that estimating the D_L from the power‐law relationship based on Taylor dispersion theory resulted in considerable errors, even in the range of Pe where the Taylor dispersion mechanism dominated. The exponent of the power‐law relationship increased as the secondary roughness was removed. Analysing the linear relationship between the D_L and Pe revealed that the longitudinal dispersivity α_L increased linearly. However, this linear increase became weak as the Taylor dispersion mechanism dominated. In the range of Pe where the macrodispersion mechanism dominated, increasing the Hurst exponent caused the increase of α_L and the secondary roughness played a significant role in enhancing the α_L. As the Taylor dispersion mechanism dominated, the α_L was insensitive to the influence of multiscale roughness in variable‐aperture fractures.  相似文献   

Penetration modeling of ultra-high performance concrete using multiscale meshfree methods     

Paul A. Sparks  Jesse A. Sherburn  William F. Heard  Brett A. Williams 《国际地质力学数值与分析法杂志》2019,43(14):2328-2351

Terminal ballistics of concrete is of extreme importance to the military and civil communities. Over the past few decades, ultra-high performance concrete (UHPC) has been developed for various applications in the design of protective structures because UHPC has an enhanced ballistic resistance over conventional strength concrete. Developing predictive numerical models of UHPC subjected to penetration is critical in understanding the material's enhanced performance. This study employs the advanced fundamental concrete (AFC) model, and it will run inside the reproducing kernel particle method (RKPM)-based code known as the nonlinear meshfree analysis program (NMAP). NMAP is advantageous for modeling impact and penetration problems that exhibit extreme deformation and material fragmentation. A comprehensive experimental study was conducted to characterize the UHPC. The investigation consisted of fracture toughness testing, the utilization of nondestructive microcomputed tomography analysis, and lastly projectile penetration shots on the UHPC targets. To improve the accuracy of the model, a new scaled damage evolution law (SDEL) is employed within the microcrack informed damage model. During the homogenized macroscopic calculation, the corresponding microscopic cell needs to be dimensionally equivalent to the mesh dimension when the partial differential equation becomes ill posed and strain softening ensues. To ensure arbitrary mesh geometry for which the homogenized stress-strain curves are derived, a size scaling law is incorporated into the homogenized tensile damage evolution law. This ensures energy-bridging equivalence of the microscopic cell to the homogenized medium irrespective of arbitrary mesh geometry. Results of numerical investigations will be compared with results of penetration experiments.  相似文献   

Analysing the influences of ENSO and PDO on water discharge from the Yangtze River into the sea          下载免费PDF全文

Jun Peng  Xiangxin Luo  Feng Liu  Zihao Zhang 《水文研究》2018,32(8):1090-1103

The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are two important climate oscillations that affect hydrological processes at global and regional scales. However, few studies have attempted to identify their single and combined influences on water discharge variability at multiple timescales. In this study, we examine temporal variation in water discharge from the Yangtze River into the sea and explore the influence of the ENSO and the PDO on multiscale variations in water discharge over the last century. The results of the wavelet transform analysis of the water discharge series show significant periodic variations at the interannual timescale of 2 to 8 years and the decadal timescale of 15 to 17 years. Water discharge tended to be higher during the La Niña–PDO cold phase and lower during the El Niño–PDO warm phase. The results of the cross wavelet spectrum and wavelet coherence analyses confirm the relationship between the interannual (i.e., 2 to 8 years) and decadal (i.e., 15 to 17 years) periodicities in water discharge with the ENSO and the PDO, respectively. As an important large‐scale climate background, the PDO can modulate the influence of the ENSO on water discharge variability. In general, the warm PDO enhances the influence of El Niño events, and the cold PDO enhances the influence of La Niña events. Our study is helpful in understanding the influencing mechanism of climate change on hydrological processes and provides an important scientific guideline for water resource prediction and management.  相似文献   

基于第二代Curvelet变换的面波压制(英文)   总被引：3，自引：2，他引：1  

郑静静  印兴耀  张广智  武国虎  张作胜 《应用地球物理》2010,7(4):325-335

针对面波能量强、频率低、视速度低等特点,本文提出了基于第二代Curvelet变换的多尺度、多方向分解的面波压制方法,充分利用Curvelet变换的多尺度、多方向功能,分离出含有面波的尺度和方向然后利用面波与有效波在Curvelet域基本不重叠的特性,进行信噪分离处理。这种方法在实际叠前地震数据的处理中,能够有效压制面波,同时较好地保护有效反射波,特别是反射波的低频分量。文中提出的基于第二代Curvelet变换的去面波方法是一种较好的保幅去噪方法。  相似文献   

基于多尺度的老采空区上方建筑物变形分析及预报   总被引：2，自引：0，他引：2  

张安兵  高井祥  张兆江 《岩土力学》2011,32(8):2423-2428

老采空区上方地表变形是一个具有复杂性、突然性和长期性等显著特点的非线性过程。在老采空区上方建设生活或服务设施时,必须对老采空区上方地基稳定性和残余变形情况进行评价和预测。基于多尺度经验模态分解（EMD）,提出了老采空区上方地表建筑物稳定性分析及预测新方法。通过实例研究,证实采用多尺度经验模态分解可获得老采空区上方地表建筑物的动态变形细部信号。对各分解尺度进行分析能更准确有效地评价原始数据所反映的建筑物变形特征和进行变形机制研究。同时,实例计算也证实,采用考虑多尺度特征的预测模型可获得比传统方法更优的变形预报精度,为更科学地评价老采空区建筑物稳定性提供理论依据。  相似文献   

1950-2008年黄河入海水沙变化(英文)   总被引：1，自引：0，他引：1  

刘锋  陈沈良  彭俊  陈广泉 《地理学报(英文版)》2011,21(6):1047-1061

Based on hydrological data observed at Lijin gauging station from 1950 to 2008, the temporal changes of water discharge and sediment load of the Yellow River into the sea were analyzed by the wavelet analysis, and their impacts on the estuary were investigated in different periods based on the measured coastline and bathymetry data. The results show that: (1) there were three significant periodicities, i.e. annual (0.5-1.0-year), internnual (3.0-6.5-year) and decadal (10.1-14.2-year), in the variations of w...  相似文献   

An efficient numerical model for hydrodynamic parameterization in 2D fractured dual-porosity media     

《Advances in water resources》2014

This paper presents a robust and efficient numerical model for the parameterization of the hydrodynamic in fractured porous media. The developed model is based upon the refinement indicators algorithm for adaptive multi-scale parameterization. For each level of refinement, the Levenberg–Marquardt method is used to minimize the difference between the measured and predicted data that are obtained by solving the direct problem with the mixed finite element method. Sensitivities of state variables with respect to the parameters are calculated by the sensitivity method. The adjoint-state method is used to calculate the local gradients of the objective function necessary for the computation of the refinement indicators. Validity and efficiency of the proposed model are demonstrated by means of several numerical experiments. The developed numerical model provides encouraging results, even for noisy data and/or with a reduced number of measured heads.  相似文献   

地震资料波阻抗多尺度融合反演   总被引：10，自引：10，他引：0       下载免费PDF全文

杨光大  陈湛文 《地球物理学进展》2005,20(3):718-723

本文依据最佳约束反演策略,应用波动方程多尺度反演方法反演中频段波阻抗.利用神经网络技术实现对中频段波阻抗的标定及高、中、低频波阻抗的融合,避免了因高、中、低频波阻抗频段重叠及中频段波阻抗精度低所造成的反演结果的误差.这种方法具有对初始模型依赖性低、收敛速度快、反演结果稳定、抗噪能力强等特点.  相似文献