Sediment variability and bed material sampling in gravel-bed rivers     

M. P. Mosley  D. S. Tindale 《地球表面变化过程与地形》1985,10(5):465-482

In a 350 m wide reach of the braided, gravel-bed Ashley River, the surface layer of the bed material was sampled in 141 areas of homogeneous graded sediment along seven cross-sections, and 30 kg bulk samples were collected at 86 randomly selected locations along the cross-sections. At one location, a single 854 kg sample composed of 28 subsamples was also collected. Analysis of the single large sample indicate that accurate determination of mean grain size D at that site requires, desirably, a sample of ～ 100 kg, but that samples in which the weight of the largest stone is less than 5 per cent of the total weight have unbiased estimates of D. Spatial variability of bulk material is such that 228 and 50 samples are needed to estimate D to ± 10 and ± 20 per cent respectively of the true value; requirements for estimating inclusive graphic standard duration are only 11 and 3 respectively. The grain-size distribution of the surface layer is only weakly related to the bulk material beneath. The results of ‘Wolman sampling’ along 12 cross-sections at two pace intervals (average 120 stones per cross-section) indicate that estimation of overall surface D to ±10 and ±20 per cent would require sampling along 64 and 14 cross-sections respectively. It is concluded that accurate characterization of bed sediment in gravel-bed rivers is very demanding of labour and resources, and that careful planning is needed to ensure efficiency and meaningful results.  相似文献   

Sampling design optimization for spatial functions   总被引：4，自引：0，他引：4  

Ricardo A. Olea 《Mathematical Geology》1984,16(4):369-392

A new procedure is presented for minimizing the sampling requirements necessary to estimate a mappable spatial function at a specified level of accuracy. The technique is based on universal kriging, an estimation method within the theory of regionalized variables. Neither actual implementation of the sampling nor universal kriging estimations are necessary to make an optimal design. The average standard errorand maximum standard error of estimationover the sampling domain are used as global indices of sampling efficiency. The procedure optimally selects those parameters controlling the magnitude of the indices, including the density and spatial pattern of the sample elements and the number of nearest sample elements used in the estimation. As an illustration, the network of observation wells used to monitor the water table in the Equus Beds of Kansas is analyzed and an improved sampling pattern suggested. This example demonstrates the practical utility of the procedure, which can be applied equally well to other spatial sampling problems, as the procedure is not limited by the nature of the spatial function.  相似文献   

核物探X射线荧光技术在Pb、Zn矿勘查中的研究与应用     

葛良全  谢庭周 《现代地质》1994,8(3):335-341

本文论述了应用核物探Ｘ射线荧光技术勘查Ｐｂ、Ｚｎ矿的物理基础、地质－地球化学依据和方法技术。实践表明，本技术可以现场快速进行土壤次生晕测量、岩石地球化学测量、粉末样品测量和原位测定Ｐｂ、Ｚｎ品位．  相似文献   

贝叶斯网络支持的地表参数混合反演模式研究   总被引：5，自引：0，他引：5  

屈永华  王锦地  刘素红  万华伟  周红敏  林皓波 《遥感学报》2006,10(1):6-14

基于贝叶斯网络理论，建立用于植被地表参数估计的混合反演模式，结合遥感物理模型实现了冬小麦叶片叶绿素含量（Cab）和冠层叶面积指数（LAI）的反演。用模型模拟数据以及2001年顺义遥感实验数据验证结果表明，LAI和Cab均有较好的反演精度。针对含噪声模拟数据反演结果中约有10％的噪声数据反演失败的情况，用不确定知识的处理方法有效地降低了失败点的比例。混合反演模式本质上是一个融合先验知识与观测数据的知识推理方案，本文实现了对反演过程中参数后验概率更新算法并引入热力学中的信息熵概念实现了参数后验信息动态定量计算，同时简单探讨了现阶段定量评价遥感反演过程中信息流控制存在的难点问题。  相似文献   

Ambient air measurements of six bifunctional carbonyls in a suburban area     

Ricardo Ortiz  Hiroyuki Hagino  Kazuhiko Sekiguchi  Qingyue Wang  Kazuhiko Sakamoto   《Atmospheric Research》2006,82(3-4):709

Low-molecular-weight carbonyl compounds, generated by photochemical reactions in the atmosphere and found in the exhaust of motor vehicles, have recently come to the attention of researchers because some of them are suspected carcinogens or mutagens. Six bifunctional carbonyl compounds were detected and measured in a suburban site 30 km northwest of the Tokyo metropolitan area. Samples were taken on five sunny days between 2 August and 11 August 2003 with a low-volume denuder and three-filter tandem system using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) as a sorbent. Bifunctional carbonyls were measured by gas chromatography–mass spectrometry after two derivatization processes with PFBHA and N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA). The average total (gas plus particle) concentrations were 162.8 ng m^− 3 for pyruvic acid, 113.7 ng m^− 3 for methylglyoxal, 36.0 ng m^− 3 for glycolaldehyde and 58.6 ng m^− 3 for glyoxal.  相似文献   

Influence of Site and Source Dependent Ground Motion Scenarios on the Seismic Safety of Long-span Bridges in Cologne, Germany     

Sandra M. Richwalski  Andreas Fäcke  Stefano Parolai  Lothar Stempniewski 《Natural Hazards》2006,38(1-2):237-246

An overlap in frequency between the 1D resonance frequency of sediments and the vibrational frequencies of long-span bridges might lead to a strongly increased structural response of the latter. Interference of surface waves caused by reflections at dipping interfaces may introduce additional unfavourable amplifications. Therefore, the vulnerability of two bridges crossing the Rhine River in Cologne, Germany, was assessed using ground motion scenarios computed for four profiles crossing the Lower Rhine Embayment. Due to their vibrational frequencies being in the vicinity of resonant peaks in the response spectra, the Severinsbridge showed critical loading and the bridge Cologne-Deutz even exhibited grave failure according to the dynamic FE-simulations.  相似文献   

Geochemical sampling with special reference to environmental risk assessment     

Weidong YANG Baojin ZHAO William Pulle 《中国地球化学学报》2006,25(B08):25-26

We usually conduct environmental investigation through sample study. Therefore, it is essential that samples should be representative, at all time, and of the object be studied. However, the issues of sample representativeness and sampling errors are often neglected by investigators. Based on modem geo-statistics and sampling theory, this paper addresses these issues in more detail and presents a case study related to environmental risk assessment. The issue of sample representativeness can be measured in the following three aspects： （1） whether the sample numbers are large enough to reflect the characteristics of the initial object being studied）; （2） whether the sample mass （or sample volume） is large enough to represent the original site （the local segment being sampled）; （3） whether assay portion is prepared well enough to depict the initial sample. Sample numbers are dictated by the confidence level, the variance of population and the acceptable estimation error as well as the homogeneity and the spatial continuity of population.  相似文献   

Study on the mechanism of organic pollutant degradation in water by hybrid gas-liquid discharge     

《中国地球化学学报》2006,25(B08):131-131

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Statistics of Boulder Encounters during Shaft Excavation     

D. Veneziano  J. Van Dyck 《Rock Mechanics and Rock Engineering》2006,39(4):339-358

Summary. We study the problem of boulder encounter during shaft excavation and the bias that results from directly using statistics from borehole samples without correction for probe diameter. We specifically focus on two quantities, the rate of boulder encounters λ₁ and the total length of obstructed shaft drilling L ₁. Assuming that boulders have spherical shape or cylindrical shape of a particular type, we evaluate how λ₁ and the mean and variance of L ₁ depend on the shaft diameter, the distribution of the boulder diameter, and the minimum boulder diameter that constitutes an obstruction to drilling. The statistics on L ₁ assume that the boulder centers are distributed according to a homogeneous Poisson process in space. Finally, we briefly discuss the problem of inferring the spatial density of boulders and their diameter distribution from borehole data. Both λ₁ and L ₁ increase significantly with increasing shaft diameter; hence the uncorrected statistics from borehole samples severely under-predict these two quantities during large-shaft drilling. Moreover, for typical parameter values, the mean value of L ₁ may be a significant fraction of the total shaft length.  相似文献   

Theoretical Estimation of the Critical Sampling Size for Homogeneous Ore Bodies with Small Nugget Effect     

K. Modis  K. Papaodysseus 《Mathematical Geology》2006,38(4):489-501

The aim of this work is to investigate whether it is possible to determine a critical sampling grid density for a given ore body, above which further improvement in the accuracy of the estimated ore reserves would be small or negligible. The methodology employed is based on the theory of information. First, it is proven that the range of influence, when appears in the variogram function, is a measure of the maximum variability frequency observed in the ore body. Then, a simple application of the well-known sampling theorem shows that, under certain assumptions, it is possible to define a critical sampling density as mentioned before. An approximate rule of thumb can then be stated: that critical sampling grid size is half the range of influence observed in the variogram.  相似文献