Operator error in petrographic point-count analysis: A theoretical approach     

F. Demirmen 《Mathematical Geology》1972,4(1):35-43

Operator error in petrographic point-count analysis introduces bias into the estimates of proportion in a thin section. A correction for this bias, leading to an unbiased estimator of the true proportion in that thin section, is here proposed. Operator error also affects the confidence interval, and in this situation, too, an adjustment is possible. The approach proposed requires that the probabilities associated with operator error, categorized into A-type and B-type errors, are known or assumed. The A-type operator error tends to underestimate the true proportion in a thin section, whereas the B-type operator error tends to overestimate it.  相似文献   

The role of some regional factors in the assessment of well yields from hard-rock aquifers of Fennoscandia     

Helge?HenriksenEmail author 《Hydrogeology Journal》2003,11(6):628-645

The attributes of about 13,600 hard-rock water wells were arranged in three profiles parallel to gradients of typical regional factors. These factors are thought to be of importance to groundwater yield from wells in the Fennoscandian crust and were subjected to a statistical analysis. The regional factors comprise annual rate of postglacial crustal uplift and annual average precipitation, whereas soil type, soil depth, and bedrock type are considered sub-regional and local factors. There is no clear trend in well yield along the regional gradients. The results of the statistical analysis indicate that for the typical regional variables, the rate of postglacial uplift and average annual precipitation explain not more than 11% of the observed variation in well yields. Some of these factors, and other factors not included in this study, work in opposite directions and may cancel each other out. It is concluded that other, more local factors, such as well depth, proximity to fracture-related lineaments and topography, have a greater influence on well yields in this area.

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Resumen Se ha recogido los atributos de aguas subterráneas con 13.600 años de antigüedad en tres perfiles perpendiculares a los gradientes de los factores regionales típicos, las cuales son captadas por pozos perforados en rocas duras. Se cree que estos factores tienen importancia en el rendimiento de los pozos realizados en la corteza de Fenoscandia, y han sido analizados estadísticamente. Los factores regionales comprenden la tasa anual de alzamiento postglacial y la precipitación media anual, mientras que el tipo y la profundidad del suelo, y el tipo de roca madre, son tratados como factores sub-regionales y locales. No se aprecia una tendencia clara en el rendimiento de los pozos a lo largo de los gradientes regionales. Los resultados del análisis estadístico indican que, para las variables regionales típicas, la tasa de alzamiento postglacial y la precipitación media anual explican como mucho el 11,2% de las variaciones observadas en el rendimiento de los pozos. Algunos de estos factores, así como otros no incluidos en el estudio, son de signo opuesto y pueden llegar a compensarse. Se concluye que factores diferentes, de escala más local, tales como la proximidad a lineamientos correlacionados con fracturas o la topografía, pueden afectar de forma más importante al rendimiento de los pozos en esta zona.

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Résumé Les propriétés d'environ 13,600 puits d'extraction d'eau souterraine dans le socle ont été réparties selon trois profils disposés perpendiculairement aux gradients de facteurs régionaux typiques. Ces facteurs sont considérés comme étant importants pour les rendements des puits dans le bouclier fenno-scandien et ont été soumis à une analyse statistique. Les facteurs régionaux sont le taux de soulèvement postglaciaire et les précipitations moyennes annuelles, alors que le type et l'épaisseur de sol, le type de substratum sont des facteurs sub-régionaux et locaux. Il n'existe pas de tendance dans le rendement des puits selon les gradients régionaux. Les résultats de l'analyse statistique indiquent que pour les variables régionales typiques, le taux de soulèvement postglaciaire et les précipitations moyennes annuelles n'expliquent pas plus de 11,2% de la variation observée du rendement des puits. Certains de ces facteurs, ainsi que d'autres non pris en compte dans cette étude, jouent dans des directions opposées et peuvent s'annuler l'un l'autre. En conclusion, d'autres facteurs, plus locaux, tels que la proximité de linéaments corrélés aux fractures et la topographie peuvent avoir une grande importance pour le rendement des puits dans cette région.

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Developing local measures of spatial association for categorical data   总被引：2，自引：0，他引：2  

Barry?BootsEmail author 《Journal of Geographical Systems》2003,5(2):139-160

This paper describes a procedure for extending local statistics to categorical spatial data. The approach is based on the notion that there are two fundamental characteristics of categorical spatial data; composition and configuration. Further, it is argued that, when considered locally, the latter should be measured conditionally with respect to the former. These ideas are developed for binary, gridded data. Local composition is measured by counting the numbers of cells of a particular type, while local configuration is measured by join counts. The approach is illustrated using a small, empirical data set and an ad hoc procedure is developed to deal with the impact of global spatial autocorrelation on the local statistics.The author gratefully acknowledges financial support from the GEOIDE Network of Centres of Excellence (ENV #4) and the helpful comments of three anonymous reviewers.  相似文献   

Turbulence Statistics Measurements in a Northern Hardwood Forest   总被引：3，自引：0，他引：3  

M. G. Villani  H. P. Schmid  H.-B. Su  J. L. Hutton  C. S. Vogel 《Boundary-Layer Meteorology》2003,108(3):343-364

Tower-based turbulence measurements were collected in and over a mixed hardwood forest at the University of Michigan BiologicalStation (UMBS) UMBSflux site in the northern summerof 2000. Velocity and temperature fluctuations were measured at five levels within the canopy (up to the canopy height, H = 21.4 m), using one- and three-dimensional sonic anemometers and fine-wire thermocouples. Six additional thermocouples were distributed over the canopy-layer depth. Three-dimensional velocities and sonic temperatures were also measured above the canopy at 1.6H and at 2.15H on the AmeriFlux tower located at the UMBSflux site. Vertical profiles of buoyancy flux, mean horizontal velocity, Reynolds stress, and standard deviation and skewness of velocity components were calculated. The analysis of these measurements aims at a multi-layer parameterization framework of turbulence statistics forimplementation in Lagrangian stochastic models. Turbulence profiles and power spectra above the canopy were analyzed in the context of Monin-Obukhov similarity theory (MOST) and Kolmogorov theory, as determined by stability at the top level (2.15H), to assess the extent to which surface scaling is valid as the canopy top is approached. Velocity spectra were computed to explore the potential of estimating the viscous dissipation rate, and results show that the high frequency range of the spectra above the canopy exhibits the roll-off predicted by Kolmogorov theory. Similarly, velocity standard deviations above the canopy converge to MOST predicted values toward the top level, and spectral peaks shift with stability, as expected. Within the canopy, both turbulence statistics profiles and spectral distributions follow the general known characteristics inside forests.  相似文献   

Differences in paleomagnetic interpretations due to the choice of statistical, demagnetization and correction techniques: Kapuskasing Structural Zone, northern Ontario, Canada     

Graham J. Borradaile  Tomasz Werner  France Lagroix   《Tectonophysics》2003,363(1-2):103-125

The Kapuskasing Structural Zone (KSZ) reveals a section through the Archean lower crustal granoblastic gneisses. Our new paleomagnetic data largely agree with previous work but we show that interpretations vary according to the choices of statistical, demagnetization and field-correction techniques. First, where the orientation distribution of characteristic remanence directions on the sphere is not symmetrically circular, the commonly used statistical model is invalid [Fisher, R.A., Proc. R. Soc. A217 (1953) 295]. Any tendency to form an elliptical distribution indicates that the sample is drawn from a Bingham-type population [Bingham, C., 1964. Distributions on the sphere and on the projective plane. PhD thesis, Yale University]. Fisher and Bingham statistics produce different confidence estimates from the same data and the traditionally defined mean vector may differ from the maximum eigenvector of an orthorhombic Bingham distribution. It seems prudent to apply both models wherever a non-Fisher population is suspected and that may be appropriate in any tectonized rocks. Non-Fisher populations require larger sample sizes so that focussing on individual sites may not be the most effective policy in tectonized rocks. More dispersed sampling across tectonic structures may be more productive. Second, from the same specimens, mean vectors isolated by thermal and alternating field (AF) demagnetization differ. Which treatment gives more meaningful results is difficult to decipher, especially in metamorphic rocks where the history of the magnetic minerals is not easily related to the ages of tectonic and petrological events. In this study, thermal demagnetization gave lower inclinations for paleomagnetic vectors and thus more distant paleopoles. Third, of more parochial significance, tilt corrections may be unnecessary in the KSZ because magnetic fabrics and thrust ramp are constant in orientation to the depth at which they level off, at approximately 15-km depth. With Archean geothermal gradients, primary remanences were blocked after the foliation was tilted to rise on the thrust ramp. Therefore, the rocks were probably magnetized in their present orientation; tilting largely or entirely predates magnetization.  相似文献   

A preliminary secular variation reference curve for archaeomagnetic dating in Austria     

Elisabeth Schnepp  Philippe Lanos 《Geophysical Journal International》2006,166(1):91-96

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PP/PS Wavefield separation by independent component analysis   总被引：1，自引：0，他引：1  

Mirko van der Baan 《Geophysical Journal International》2006,166(1):339-348

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Sensitivity of goodness-of-fit statistics to rainfall data rounding off     

Roberto Deidda  Michelangelo Puliga 《Physics and Chemistry of the Earth》2006,31(18):1240-1251

An analysis based on the L-moments theory suggests of adopting the generalized Pareto distribution to interpret daily rainfall depths recorded by the rain-gauge network of the Hydrological Survey of the Sardinia Region. Nevertheless, a big problem, not yet completely resolved, arises in the estimation of a left-censoring threshold able to assure a good fitting of rainfall data with the generalized Pareto distribution. In order to detect an optimal threshold, keeping the largest possible number of data, we chose to apply a “failure-to-reject” method based on goodness-of-fit tests, as it was proposed by Choulakian and Stephens [Choulakian, V., Stephens, M.A., 2001. Goodness-of-fit tests for the generalized Pareto distribution. Technometrics 43, 478-484]. Unfortunately, the application of the test, using percentage points provided by Choulakian and Stephens (2001), did not succeed in detecting a useful threshold value in most analyzed time series. A deeper analysis revealed that these failures are mainly due to the presence of large quantities of rounding off values among sample data, affecting the distribution of goodness-of-fit statistics and leading to significant departures from percentage points expected for continuous random variables. A procedure based on Monte Carlo simulations is thus proposed to overcome these problems.  相似文献   

Impacts of permafrost changes on alpine ecosystem in Qinghai-Tibet Plateau   总被引：9，自引：0，他引：9  

WANG Genxu  LI Yuanshou  WU Qingbai  WANG Yibo 《中国科学D辑(英文版)》2006,49(11):1156-1169

Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the per- mafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.11% under the permafrost environment degradation during recent 15 years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively serious degradation. Furthermore, from the angles of grassland coverage and biological production the variation characteristics of high-cold eco- systems in different representative regions and different geomorphologic units under different climatic conditions were quantitatively assessed. In the future, adopting effective measures to protect permafrost is of vital importance to maintaining the stability of permafrost engineering and alpine cold eco- systems in the plateau.  相似文献   

Recurrence Interval Statistics of Cellular Automaton Seismicity Models     

Dion Weatherley 《Pure and Applied Geophysics》2006,163(9):1933-1947

The recurrence interval statistics for regional seismicity follows a universal distribution function, independent of the tectonic setting or average rate of activity (Corral, 2004). The universal function is a modified gamma distribution with power-law scaling of recurrence intervals shorter than the average rate of activity and exponential decay for larger intervals. We employ the method of Corral (2004) to examine the recurrence statistics of a range of cellular automaton earthquake models. The majority of models has an exponential distribution of recurrence intervals, the same as that of a Poisson process. One model, the Olami-Feder-Christensen automaton, has recurrence statistics consistent with regional seismicity for a certain range of the conservation parameter of that model. For conservation parameters in this range, the event size statistics are also consistent with regional seismicity. Models whose dynamics are dominated by characteristic earthquakes do not appear to display universality of recurrence statistics.  相似文献