协方差函数的抗差拟合     

刘念 《测绘科学》2002,(3)

如果最小二乘拟合推估法被应用在重力异常、高程异常等的内插中 ,当观测值中含有粗差时 ,由此拟合的协方差函数就不能精确表征其统计性质。本文先从协方差函数的拟合过程入手 ,通过分析传统的协方差函数拟合法的无抗差性 ,提出了协方差函数的抗差拟合法  相似文献   

On Visualization for Assessing Kriging Outcomes   总被引：7，自引：0，他引：7  

James R. Carr 《Mathematical Geology》2002,34(4):421-433

Extant opinion about kriging is that all weights should be positive. Visualizations rendered by converting kriged grids to digital images are presented to show that negative weights may be beneficial to some spatial problems. In particular, variogram models with zero-valued nuggets, already well known to minimize smoothing through kriging, result in a visual resolution substantially superior to that from kriging with a variogram model having a nonzero nugget value in application to satellite acquired data. Negative weights are more likely when using variogram models with zero-valued nuggets, but resultant visualizations often show a smoother transition between extreme data values. This is true even when a variogram model having a nugget value of zero is not optimum with respect to mean square error, as is demonstrated using a nitrate data set. An analogy to digital image processing is used to suggest that the influence of negative weights in kriging is similar to a high-boost kernel.  相似文献   

Sensitivity of PSHA results to ground motion prediction relations and logic-tree weights   总被引：7，自引：0，他引：7  

Fabio Sabetta  Antonio Lucantoni  Hilmar Bungum  Julian J. Bommer 《Soil Dynamics and Earthquake Engineering》2005,25(4):317-329

Epistemic uncertainty in ground motion prediction relations is recognized as an important factor to be considered in probabilistic seismic hazard analysis (PSHA), together with the aleatory variability that is incorporated directly into the hazard calculations through integration across the log-normal scatter in the ground motion relations. The epistemic uncertainty, which is revealed by the differences in median values of ground motion parameters obtained from relations derived for different regions, is accounted for by the inclusion of two or more ground motion prediction relations in a logic-tree formalism. The sensitivity of the hazard results to the relative weights assigned to the branches of the logic-tree, is explored through hazard analyses for two sites in Europe, in areas of high and moderate seismicity, respectively. The analyses reveal a strong influence of the ground motion models on the results of PSHA, particularly for low annual exceedance frequencies (long return periods) and higher confidence levels. The results also show, however, that as soon as four or more relations are included in the logic-tree, the relative weights, unless strongly biased towards one or two relations, do not significantly affect the hazard. The selection of appropriate prediction relations to include in the analysis, therefore, has a greater impact than the expert judgment applied in assigning relative weights to the branches of the logic-tree.  相似文献   

虚拟权平差在矿山大型贯通近井网设计中的应用   总被引：1，自引：0，他引：1  

覃辉  张启苏 《四川测绘》1994,17(2):70-74,53

本文将虚拟权平差法引入矿山大型贯通近井网的设计中，解决了相距甚远的两井口近井网精度基准不统一的问题，通过对一矿山大到贯通近井网的重新设计证明：该法具有良好的应用前景．  相似文献   

扩建网统一函数模型的虚拟权平差公式   总被引：1，自引：0，他引：1  

覃辉 《四川测绘》1995,18(4):147-150

本文从混合平差的函数模型出发，推证了矿区扩建网统一函数模型的虚拟权平差公式，完善了虚拟权平差理论。  相似文献   

三维空间下的证据权建模方法与资源预测应用     

潘诗辰  毛先成 《江苏地质》2015,39(3):373-382

为了探索证据权法在三维空间下成矿预测的实际应用,在传统证据权的基础上,探讨了适用于三维空间下成矿预测的证据权建模思路和方法。并以Visual Studio 2010为开发平台,在Access 2003中建立多元地学空间数据库,开发可进行证据因子选择、因子权重计算及后验概率计算的证据权软件WofE3DSys,其输出结果可在Voxler中进行三维可视化呈现。经分析,WofE3DSys计算结果与Arc WofE输出结果在异常圈定方面基本一致,验证了WofE3DSys的准确性。最后,以招平断裂带大尹格庄金矿为实例,选取成矿信息作为证据图层,进行成矿预测。该研究是对三维空间下证据权法的一次探索,为将来该证据权法在其他矿区的成矿预测提供了现实依据  相似文献   

细胞神经网络在重力异常分异中的研究及应用   总被引：1，自引：0，他引：1  

李超  江玉乐  胡明科  蒋亚东  郑成 《物探化探计算技术》2015,(1)

介绍采用细胞神经网络CNN(cellular neural network)方法,对铬铁矿区内的矿体和围岩的重力异常进行分异。首先阐述了CNN方法的原理和算法,采用拟BP学习算法训练网络的权值,用全局误差函数求导方法推导权值的修正公式,讨论了如何根据目标异常训练适合该地质条件的网络的连接权值;其次将重力异常数据预处理,以达到适合CNN方法处理的数据格式和要求;最后由于该矿区内没有已知的重力数据作为网络训练的目标输出,根据相关地质图设置相应的地下构造模型。利用"点元"法分别正演出叠加异常和矿体异常,进而训练出适合全区的网络连接权值,实现了对全区重力异常的分异。应用结果表明,细胞神经网络方法较好地突出该矿区高异常和矿体的边界,只要选择了合适的网络连接权值,就能将横向叠加异常区分开,故CNN方法可以实现矿体和围岩的重力异常分异。  相似文献   

加权证据权模型和逐步证据权模型及其在个旧锡铜矿产资源预测中的应用   总被引：7，自引：2，他引：5  

张生元  成秋明  张素萍  夏庆霖 《地球科学》2009,34(2):281-286

为了消除和减弱当证据层不满足条件独立性假设时对预测结果产生的影响, 提出了逐步证据权模型和加权证据权模型.加权证据权模型通过对logit模型进行修改, 对各个证据层给予一定的权重, 以调整由于证据层与其他证据层的条件相关性对模型的影响; 逐步证据权模型是将证据层按照一定的顺序逐步加入到模型中, 在加入到模型的过程中依次用已经获得的后验概率作为模糊训练层的方法.以个旧锡铜多金属矿产资源预测为例, 应用4种证据权模型的后验概率进行异常圈定, 结果表明两种新的模型对减弱证据层不满足条件独立性假设所产生的影响是有效的.   相似文献   

岩体不连续面迹长与直径间的概率关系模型分析   总被引：2，自引：0，他引：2  

钱海涛  马平  秦四清 《岩土力学》2007,28(9):1828-1832

由于“随机”概念的模糊性,在假定不连续面为薄圆盘及弦长作为迹长的前提下,基于迹线端点在圆周上均匀分布、迹线中点在直径上均匀分布、迹线中点在圆面域内均匀分布这3种明确而又不同的“随机”含义,可以得到3种合理的迹长 与直径 间的概率关系模型。通过对这3种模型进行分析认为：其在各自的“随机”含义下都是正确的,只是适用条件各异;野外实际可行的条件是介于模型2 和模型3之间的,合理地分析应该同时考虑这两种模型。在实际应用中,应该首先对所有取样面产状之间的关系进行分析,根据其结果来分配给模型2和模型3以某种权重,这样得到的迹长与不连续面直径之间概率关系更具合理性,其结果弥补了目前国内外进行的相关研究仅仅考虑到第2类模型的不足。  相似文献   

A Comparison of the Weights-of-Evidence Method and Probabilistic Neural Networks   总被引：1，自引：0，他引：1  

Singer  Donald A.  Kouda  Ryoichi 《Natural Resources Research》1999,8(4):287-298

The need to integrate large quantities of digital geoscience information to classify locations as mineral deposits or nondeposits has been met by the weights-of-evidence method in many situations. Widespread selection of this method may be more the result of its ease of use and interpretation rather than comparisons with alternative methods. A comparison of the weights-of-evidence method to probabilistic neural networks is performed here with data from Chisel Lake-Andeson Lake, Manitoba, Canada. Each method is designed to estimate the probability of belonging to learned classes where the estimated probabilities are used to classify the unknowns. Using these data, significantly lower classification error rates were observed for the neural network, not only when test and training data were the same (0.02 versus 23%), but also when validation data, not used in any training, were used to test the efficiency of classification (0.7 versus 17%). Despite these data containing too few deposits, these tests of this set of data demonstrate the neural network's ability at making unbiased probability estimates and lower error rates when measured by number of polygons or by the area of land misclassified. For both methods, independent validation tests are required to ensure that estimates are representative of real-world results. Results from the weights-of-evidence method demonstrate a strong bias where most errors are barren areas misclassified as deposits. The weights-of-evidence method is based on Bayes rule, which requires independent variables in order to make unbiased estimates. The chi-square test for independence indicates no significant correlations among the variables in the Chisel Lake–Andeson Lake data. However, the expected number of deposits test clearly demonstrates that these data violate the independence assumption. Other, independent simulations with three variables show that using variables with correlations of 1.0 can double the expected number of deposits as can correlations of –1.0. Studies done in the 1970s on methods that use Bayes rule show that moderate correlations among attributes seriously affect estimates and even small correlations lead to increases in misclassifications. Adverse effects have been observed with small to moderate correlations when only six to eight variables were used. Consistent evidence of upward biased probability estimates from multivariate methods founded on Bayes rule must be of considerable concern to institutions and governmental agencies where unbiased estimates are required. In addition to increasing the misclassification rate, biased probability estimates make classification into deposit and nondeposit classes an arbitrary subjective decision. The probabilistic neural network has no problem dealing with correlated variables—its performance depends strongly on having a thoroughly representative training set. Probabilistic neural networks or logistic regression should receive serious consideration where unbiased estimates are required. The weights-of-evidence method would serve to estimate thresholds between anomalies and background and for exploratory data analysis.  相似文献