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61.
Conditioning temperature‐index model parameters on synoptic weather types for glacier melt simulations 下载免费PDF全文
T. Matthews R. Hodgkins R. L. Wilby S. Guðmundsson F. Pálsson H. Björnsson S. Carr 《水文研究》2015,29(6):1027-1045
Temperature‐index models are widely favoured as a pragmatic means of simulating glacier melt because of their generally good performance, computational simplicity and limited demands for in situ data. However, their coefficients are normally treated as temporally stationary, unrealistically assuming a constancy of the prevailing weather. We address this simplification by prescribing model coefficients as a function of synoptic weather type, in a procedure that utilizes reanalysis data and preserves the minimal data requirements of temperature‐index models. Using a cross‐validation procedure at Vestari Hagafellsjökull, Iceland, and Storglaciären, Sweden, we demonstrate that applying transient model coefficients, for three temperature‐index models, results in statistically significant increases in the skill with which melt is modelled: Median simulation improvements in the Nash–Sutcliffe efficiency coefficient of 7.3 and 23.6% are achieved when hourly and daily melt totals are evaluated respectively. Our weather‐type modelling approach also yields insight to processes driving parameter variability, revealing dependence that is consistent with a priori considerations of the surface energy balance. We conclude that incorporating weather types into temperature‐index models holds promise for improving their performance, as well as enhancing understanding variability in coefficient values. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
62.
The Markov chain random field (MCRF) model is a spatial statistical approach for modeling categorical spatial variables in multiple dimensions. However, this approach tends to be computationally costly when dealing with large data sets because of its sequential simulation processes. Therefore, improving its computational efficiency is necessary in order to run this model on larger sizes of spatial data. In this study, we suggested four parallel computing solutions by using both central processing unit (CPU) and graphics processing unit (GPU) for executing the sequential simulation algorithm of the MCRF model, and compared them with the nonparallel computing solution on computation time spent for a land cover post-classification. The four parallel computing solutions are: (1) multicore processor parallel computing (MP), (2) parallel computing by GPU-accelerated nearest neighbor searching (GNNS), (3) MP with GPU-accelerated nearest neighbor searching (MP-GNNS), and (4) parallel computing by GPU-accelerated approximation and GPU-accelerated nearest neighbor searching (GA-GNNS). Experimental results indicated that all of the four parallel computing solutions are at least 1.8× faster than the nonparallel solution. Particularly, the GA-GNNS solution with 512 threads per block is around 83× faster than the nonparallel solution when conducting a land cover post-classification with a remotely sensed image of 1000?×?1000 pixels. 相似文献
63.
One of the common sources of error in triaxial tests is the penetration of the latex membrane into the peripheral voids of the specimen as confining pressure is applied. Existing analytical solutions developed to predict the magnitude of this membrane penetration have all assumed that the peripheral sand particles in contact with the surrounding membrane are arranged so that the centroids of the sand–membrane contact areas form a square pattern of side length D50 on a plane parallel to the undeflected membrane. Measurements made on digital images of sand–membrane contact patterns for triaxial specimens of varying characteristics have shown this assumption to be inadequate. The analysis presented herein shows how actual contact pattern can be reasonably replicated by simulated patterns. These simulated patterns are generated by adding randomly selected distances to the centroid co‐ordinates of contact areas initially placed in a systematic grid pattern. The results indicate that it is possible to systematically model sand–membrane contact patterns as a function of triaxial specimen characteristics such as relative density and preparation method. The ability to simulate the real patterns eliminates the reliance of existing analytical solutions on a single assumed square contact pattern and hence can serve as the basis for improving the accuracy of future solutions to account for the effects of membrane penetration. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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65.
空间最近目标查找算法分析及其高性能Web实现 总被引:1,自引:1,他引:0
讨论了空间最近目标查找的基本算法和相关的空间索引机制,简单地比较了几种算法和索引机制的优缺点.详细地介绍了在Windows IIS和.Net下,建立多级空间格网索引,实现空间最近目标查找的实现方法. 相似文献
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Because of the need for computational efficiency, bivariate interpolation methods applied to scattered observations often involve two stages. Initially the variable is estimated at regular grid nodes using a running subset of data (usually of fixed number). This, however, will produce discontinuities in the interpolated surface. Thus a second stage, curvilinear interpolation technique, is applied to estimated values to smooth out the effect of discontinuities. Such problems can be overcome efficiently in processing large data sets by interpolating over natural neighbor subsets. Interpolation procedures that generate discontinuities in the interpolated surface are inappropriate for geological applications, where dislocations due to structural complications may be present. 相似文献
68.
《水文科学杂志》2013,58(6)
Abstract Abstract An approach was developed for combining streamflow drought information from synthetic (generated) data with data reconstructed based on palaeoclimatic information (tree ring widths). The tree ring data were used to reconstruct streamflow in periods when no streamflow data were collected. The reconstructed data were then used as a source of historical data for estimating drought severity quantiles. The generated data were obtained using a nearest neighbour resampling method while the tree ring reconstruction was accomplished using a regression model. The application of the approach was to data from the Athabasca River in Alberta, Canada. The results demonstrate the feasibility and the utility of the approach for obtaining more accurate and precise estimates of extreme drought severity quantiles. 相似文献
69.
为提高新安江模型的汇流计算精度并减少经验因素对参数率定的影响,将新安江产流模型与改进的BP汇流模型相耦合,建立XBK(XAJ-BP-KNN)模型。该模型以前期模拟流量和新安江产流模型计算的产流量作为BP网络的输入,出口断面流量作为网络输出,拟合汇流的非线性关系,代替新安江模型的分水源、线性水库及河道马斯京根法的汇流计算;采用相似原理和K-最近邻算法,基于历史样本的模拟误差及相应影响要素对网络输出进行误差修正,实现了无前期实测流量的连续模拟;模型使用SCE-UA算法与遗传早停止LM算法相结合的全局优化方法进行参数优选。在呈村流域的验证表明XBK模型的模拟精度高于新安江模型,全局优化方法能找到最优参数,降低了模型的使用难度。 相似文献
70.
格网单元的编码计算是全球离散网格系统的核心,支撑着网格快速索引及应用分析的高效计算。Hilbert曲线具有聚簇性高、连续性强的特点,是研究设计全球离散网格编码的重要工具。利用Hilbert曲线进行格元编码实现了坐标等效降维表达,但是对Hilbert曲线不同层级之间的变换关系、一维Hilbert码如何刻画格元多维空间结构与关系等网格编码基础理论问题的研究尚不完备。本文以八叉树立体网格中三维Hilbert曲线层级演进关系为突破口,使用状态矩阵与演进矩阵构建层级演进模型,进而分别设计笛卡儿坐标至Hilbert码计算以及邻近格元Hilbert码计算方法。与现有算法对比,本文算法以层级演进模型为理论基础,避免了烦琐迭代步骤以及转换步骤,算法流程简明直接。试验结果表明,本文笛卡儿坐标至Hilbert码计算效率较迭代算法提高为7%~23%,邻近格元Hilbert码计算效率较转换算法提高4.0~4.5倍。 相似文献