Geo-scape,a granularity depended spatialization tool for visualizing multidimensional data sets     

Kontaxaki Sofia  Kokla Margarita  Kavouras Marinos 《地球空间信息科学学报》2010,13(4):275-284

Recently,the expertise accumulated in the field of geovisualization has found application in the visualization of abstract multidimensional data,on the basis of methods called spatialization methods.Spatialization methods aim at visualizing multidimensional data into low-dimensional representational spaces by making use of spatial metaphors and applying dimension reduction techniques.Spatial metaphors are able to provide a metaphoric framework for the visualization of information at different levels of gran...  相似文献   

Sensitivity of soil parameters in unsaturated zone modelling and the relation between effective,laboratory and in situ estimates     

J. Mertens  H. Madsen  M. Kristensen  D. Jacques  J. Feyen 《水文研究》2005,19(8):1611-1633

Simulation of soil moisture content requires effective soil hydraulic parameters that are valid at the modelling scale. This study investigates how these parameters can be estimated by inverse modelling using soil moisture measurements at 25 locations at three different depths (at the surface, at 30 and 60 cm depth) on an 80 by 20 m hillslope. The study presents two global sensitivity analyses to investigate the sensitivity in simulated soil moisture content of the different hydraulic parameters used in a one‐dimensional unsaturated zone model based on Richards' equation. For estimation of the effective parameters the shuffled complex evolution algorithm is applied. These estimated parameters are compared to their measured laboratory and in situ equivalents. Soil hydraulic functions were estimated in the laboratory on 100 cm³ undisturbed soil cores collected at 115 locations situated in two horizons in three profile pits along the hillslope. Furthermore, in situ field saturated hydraulic conductivity was estimated at 120 locations using single‐ring pressure infiltrometer measurements. The sensitivity analysis of 13 soil physical parameters (saturated hydraulic conductivity (K_s), saturated moisture content (θ_s), residual moisture content (θ_r), inverse of the air‐entry value (α), van Genuchten shape parameter (n), Averjanov shape parameter (N) for both horizons, and depth (d) from surface to B horizon) in a two‐layer single column model showed that the parameter N is the least sensitive parameter. K_s of both horizons, θ_s of the A horizon and d were found to be the most sensitive parameters. Distributions over all locations of the effective parameters and the distributions of the estimated soil physical parameters from the undisturbed soil samples and the single‐ring pressure infiltrometer estimates were found significantly different at a 5% level for all parameters except for α of the A horizon and K_s and θ_s of the B horizon. Different reasons are discussed to explain these large differences. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

轨道线性拟合在星载InSAR基线估计中的应用分析          下载免费PDF全文

郑浩  秦显平 《海洋测绘》2010,30(1):32-34

轨道线性拟合法具有模型严密、求解精度高等优点。对轨道线性拟合在星载InSAR基线估计中的可行性进行了分析,证明轨道线性拟合可以满足星载InSAR干涉测量的精度要求。  相似文献   

Towards a comprehensive approach to parameter estimation in land surface parameterization schemes     

Rafael Rosolem  Hoshin V. Gupta  W. James Shuttleworth  Luis Gustavo Gonçalves de Gonçalves  Xubin Zeng 《水文研究》2013,27(14):2075-2097

In climate models, the land–atmosphere interactions are described numerically by land surface parameterization (LSP) schemes. The continuing improvement in realism in these schemes comes at the expense of the need to specify a large number of parameters that are either directly measured or estimated. Also, an emerging problem is whether the relationships used in LSPs are universal and globally applicable. One plausible approach to evaluate this is to first minimize uncertainty in model parameters by calibration. In this paper, we conduct a comprehensive analysis of some model diagnostics using a slightly modified version of the Simple Biosphere 3 model for a variety of biomes located mainly in the Amazon. First, the degree of influence of each individual parameter in simulating surface fluxes is identified. Next, we estimate parameters using a multi‐operator genetic algorithm applied in a multi‐objective context and evaluate simulations of energy and carbon fluxes against observations. Compared with the default parameter sets, these parameter estimates improve the partitioning of energy fluxes in forest and cropland sites and provide better simulations of daytime increases in assimilation of net carbon during the dry season at forest sites. Finally, a detailed assessment of the parameter estimation problem was performed by accounting for the decomposition of the mean squared error to the total model uncertainty. Analysis of the total prediction uncertainty reveals that the parameter adjustments significantly improve reproduction of the mean and variability of the flux time series at all sites and generally remove seasonality of the errors but do not improve dynamical properties. Our results demonstrate that error decomposition provides a meaningful and intuitive way to understand differences in model performance. To make further advancements in the knowledge of these models, we encourage the LSP community to adopt similar approaches in the future. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Assessing uncertainties in a conceptual water balance model using Bayesian methodology / Estimation bayésienne des incertitudes au sein d’une modélisation conceptuelle de bilan hydrologique     

《水文科学杂志》2013,58(1)

Abstract

Abstract The aim of this study was to estimate the uncertainties in the streamflow simulated by a rainfall–runoff model. Two sources of uncertainties in hydrological modelling were considered: the uncertainties in model parameters and those in model structure. The uncertainties were calculated by Bayesian statistics, and the Metropolis-Hastings algorithm was used to simulate the posterior parameter distribution. The parameter uncertainty calculated by the Metropolis-Hastings algorithm was compared to maximum likelihood estimates which assume that both the parameters and model residuals are normally distributed. The study was performed using the model WASMOD on 25 basins in central Sweden. Confidence intervals in the simulated discharge due to the parameter uncertainty and the total uncertainty were calculated. The results indicate that (a) the Metropolis-Hastings algorithm and the maximum likelihood method give almost identical estimates concerning the parameter uncertainty, and (b) the uncertainties in the simulated streamflow due to the parameter uncertainty are less important than uncertainties originating from other sources for this simple model with fewer parameters.  相似文献   

统计检验抗差估计新方法研究   总被引：1，自引：0，他引：1  

郑勇波  周命端  文鸿雁 《测绘科学》2010,35(5):72-73

20世纪60年代数学家重新从广泛的意义上提出非最小二乘估计问题,并已在抗差估计中取得重要的进展。从1980年起,抗差估计理论开始被引入测量领域,并出现了许多方案。本文依据统计检验,结合IGG1区间划分的部分思想,提出了一种全新的定权思路,给出了一个简要数学模型。利用MATLAB编程,将本文提出的方法与经典的IGG1方法进行了比较,对它的抗差效果进行了总结分析,通过一个经典算例,表明新方法具有准确定位粗差的优点。  相似文献   

中国大地测量数据处理60年重要进展 第二部分:大地测量参数估计理论与方法的主要进展   总被引：4，自引：1，他引：3  

杨元喜  张丽萍 《地理空间信息》2010,8(1):1-6

大地测量参数估计原理是大地测量数据处理的重要基础。中国学者经过60年不懈努力,在自由网平差、拟稳平差、半参数估计、不适定问题解算方法、抗差估计、自适应滤波等领域做出了重要贡献,建立了许多新的理论、模型和方法,推进了大地测量数据处理理论的进展。这一部分重点介绍建国60年来中国学者在大地测量数据处理原理、方法方面取得的成就。  相似文献   

双步抗差估计及其应用     

刘兴春  仲健民  孙立军 《全球定位系统》2010,35(2):33-35

抗差估计是一种可以有效抵制粗差影响的平差方法。但权因子函数的临界值定值问题较为困难，若选取不当，会造成法方程系数阵秩亏或粗差观测值的影响未能完全消除，从而导致平差无法进行或抗差不彻底。针对上述问题提出了一种改进型抗差估计法一双步抗差估计法，并通过对一边角网和一实测GPS向量网进行的试算，验证了双步抗差估计的优越性。  相似文献   

预处理共轭梯度法解病态问题及在GPS中的应用     

张同兵  谢建  朱建军 《测绘工程》2010,19(4):60-63

介绍测量数据处理中病态问题的岭估计思想及确定岭参数的方法。引入预处理共轭梯度法求解病态法方程组,说明算法的基本原理和它能有效减弱病态性的原因。用一个GPS差分动态定位的实例,通过与不同岭估计方法的对比分析,验证该方法是一个有效的数值迭代算法。  相似文献   

On bandwidth selection for nonparametric estimation in flood frequency analysis     

A. Quintela‐del‐Río 《水文研究》2011,25(5):671-678

  相似文献