Rainfall estimation using raingages and radar — A Bayesian approach: 1. Derivation of estimators

Procedures for estimating rainfall from radar and raingage observations are constructed in a Bayesian framework. Given that the number of raingage measurements is typically very small, mean and variance of gage rainfall are treated as uncertain parameters. Under the assumption that log gage rainfall and log radar rainfall are jointly multivariate normal, the estimation problem is equivalent to lognormal co-kriging with uncertain mean and variance of the gage rainfall field.The posterior distribution is obtained under the assumption that the prior for the mean and inverse of the variance of log gage rainfall is normal-gamma 2. Estimate and estimation variance do not have closed-form expressions, but can be easily evaluated by numerically integrating two single integrals. To reduce computational burden associated with evaluating sufficient statistics for the likelihood function, an approximate form of parameter updating is given. Also, as a further approximation, the parameters are updated using raingage measurements only, yielding closed-form expressions for estimate and estimation variance in the Gaussian domain.With a reduction in the number of radar rainfall data in constructing covariance matrices, computational requirements for the estimation procedures are not significantly greater than those for simple co-kriging. Given their generality, the estimation procedures constructed in this work are considered to be applicable in various estimation problems involving an undersampled main variable and a densely sampled auxiliary variable.     

Binomial model on seismic risk analysis

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Coastal slope terracing and relative sea-level changes: Deductions based on computer simulations

Although a traditional geological survey of terraced coastal slopes is an essential part of studies aimed to reconstruct relative sea-level changes, the stratigraphic and chronological data so obtained frequently prove inadequate to completely unravel the sometimes very complex history of sea-level fluctuation, especially where erosion has prevailed over deposition and/or deposits are difficult to date. On the basis of our experience we think that much additional information can be gained through geomorphological interpretation of the profiles of those slopes. In order to facilitate such interpretation, a computer simulation model is developed that is able to predict the morphogenic response to a variety of possible relative-sea-level histories. The results can be used to envisage some new interpretation keys for the analysis of real situations and, hopefully, as bases for the conception of general models of coastal slope evolution under the action of a variable sea level. Though preliminary, the results so far obtained permit identification of the geomorphological consequences (in terms of resulting slope profile) of ordered successions of transgressions and regressions of different amplitude, rate, order and style. Moreover they provide interesting insights into the role that different styles of tectonic uplift may play in the phenomenon of multiple terracing of coastal slopes.     

Probabilistic Assessment of Temperature in the Euganean Geothermal Area (Veneto Region, NE Italy)

In the geothermal Euganean area (Veneto region, NE Italy) water temperatures range from 60 to 86°C. The aquifer considered is rocky and the production wells in this study have a depth ranging from 300 to 500 m. For exploitation purposes, it is important to identify zones with a high probability that the temperature is more than 80°C and zones with a high probability that the temperature is less than 70°C. First, variographic analysis was conducted from 186 temperature data of thermal ground waters. This analysis gave results that are consistent with the main regional tectonic structure, the NW-SE trending Schio-Vicenza fault system. Then indicator variograms of the second, fifth, and eighth decile were compared to identify the spatial continuity at different thresholds. The unacceptability of a multigaussian hypothesis of the random function and the necessity to know the cumulative distribution function in any location, suggested the use of a nonparametric geostatistical procedure such as indicator kriging. Thus, indicator variograms at the cutoffs of 65, 70, 73, 75, 78, 80, 82, and 84°C were analyzed, fitted, and used during the indicator kriging procedure. Finally, probability maps were derived from postprocessing indicator kriging results. These maps identified scarcely exploited areas with a high probability of the temperature being higher than 80°C, between 70 and 80°C and areas with high probability of the temperature being below 70°C.     

火焰原子吸收光谱法测定铜精矿中银含量的测量不确定度评定

采用《测量不确定度评定与表示指南》，以火焰原子吸收光谱法测定铜精矿中的银含量为例，对测量结果进行不确定度评定。分析了不确定度的重要来源，包括称样质量、标准工作溶液、工作曲线拟合、试液定容体积及测量重复性等引入的不确定度分量组成。对各不确定度分量进行分析计算，求得标准不确定度为1．56，扩展不确定度为3．12。     

Solute and isotope constraint of groundwater recharge simulation in an arid environment,Abu Dhabi Emirate,United Arab Emirates

A simple, well-constrained simulation of solute increases in a downgradient direction was used in the shallow unconfined aquifer of eastern Abu Dhabi Emirate (United Arab Emirates). The simulation indicates that the observed exponential increase in solute concentrations results from a combination of upward transport of solutes from underlying mudstones and evaporites, and groundwater losses by evaporation. Groundwater recharge and discharge flux in unconfined regional aquifers in arid regions commonly are difficult to estimate because there are few constraints on the flux of water lost or gained from the system. Total dissolved solids (TDS) and deuterium isotopes (δ²H) in groundwater are used to constrain estimated fluxes to the shallow aquifer of eastern Abu Dhabi Emirate. Vertical upward transport of solutes from underlying mudstones and evaporites accounts for solute increases along approximately the first 80 km of the simulated flow path, but a combination of upward solute transport and evaporation is necessary to explain observed solute concentrations beyond 80 km. Mobilization and transport of solutes in the unsaturated zone by recharging precipitation is not a significant factor.

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Résumé Une simulation simple et bien contrainte de l’augmentation des solutés dans la direction de l’écoulement a été réalisée sur l’aquifère phréatique et libre de l’Est de l’émirat d’Abu Dhabi (émirats Arabes Unis). La simulation indique que l’augmentation observée de solutés, de forme exponentielle, est le produit de la combinaison du transport ascendant de solutés provenant des mudstones et des évaporites sous-jacents, et de l’évaporation des eaux souterraines. La recharge des eaux souterraines et les flux de vidange dans les aquifères régionaux libres des régions arides sont habituellement difficiles à estimer du fait du peu de contraintes agissant sur la perte ou le gain d’eau dans le système. La charge dissoute totale (TDS, en anglais) et les isotopes deutérium (δ²H) des eaux souterraines sont utilisés pour contraindre l’estimation des flux en direction de l’aquifère phréatique de l’Est de l’émirat d’Abu Dhabi. Le transport vertical ascendant des solutés à partir des mudstones et des évaporites fait parti des processus qui concentrent les solutés approximativement le long des 80 premiers kilomètres du trajet des écoulements simulés, mais une combinaison du transport ascendant des solutés et de l’évaporation est nécessaire pour expliquer les concentrations observées en soluté au delà des 80 km. La mobilisation et le transport des solutés par les précipitations efficaces dans la zone non saturée ne représentent pas des facteurs significatifs.

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Resumen Se utilizó una simulación simple y muy restringida, de incrementos de soluto en la dirección del flujo, en el acuífero libre poco profundo del Emirato oriental de Abu Dhabi, (Emiratos árabes Unidos). La simulación indica que el aumento exponencial observado en las concentraciones del soluto, resulta de una combinación de transporte ascendente de solutos desde las evaporitas y lodolitas subyacentes, y por pérdidas del agua subterránea por evaporación. Los flujos de recarga y descarga de agua subterránea, en los acuíferos libres regionales en regiones áridas, normalmente son difíciles estimar, porque hay algunas restricciones en el flujo de agua perdido o ganado por el sistema. Los sólidos disueltos totales (TDS) y los isótopos de deuterio (δ²H) en el agua subterránea, se usan para forzar los flujos estimados hacia el acuífero poco profundo del Emirato oriental de Abu Dhabi. El transporte ascendente vertical de solutos desde las lodolitas y evaporitas subyacentes, involucra los aumentos del soluto a lo largo de aproximadamente los primeros 80 Km. de la dirección de flujo simulada, pero es necesaria una combinación de transporte ascendente del soluto y la evaporación para explicar las concentraciones del soluto observadas más allá de 80 Km. La movilización y transporte de solutos en la zona no saturada, por recarga debida a precipitación, no es un factor significante.

     

Utility Efficient Frontier: An Application in the Oil and Gas Industry

Current practice shows that the use of portfolio and utility theory is very low among petroleum companies. This article advocates the use of both portfolio theory and utility theory as decision-making tools to improve performance of oil and gas companies. We introduce a model that can be practically used and applied in the oil and gas industry. This model generates an optimized, efficient portfolio and, at the same time, enables the decision maker to incorporate his risk attitude and policy. This can only be done by combining both the portfolio theory and utility theory through an approach called the utility mean-variance model. A typical oil portfolio optimization problem is investigated by applying both portfolio and utility theories. Through the utility mean-variance model, an efficient frontier that captures decision maker risk attitude is achieved.     

Logic-tree Approach for Probabilistic Tsunami Hazard Analysis and its Applications to the Japanese Coasts

For Probabilistic Tsunami Hazard Analysis (PTHA), we propose a logic-tree approach to construct tsunami hazard curves (relationship between tsunami height and probability of exceedance) and present some examples for Japan for the purpose of quantitative assessments of tsunami risk for important coastal facilities. A hazard curve is obtained by integration over the aleatory uncertainties, and numerous hazard curves are obtained for different branches of logic-tree representing epistemic uncertainty. A PTHA consists of a tsunami source model and coastal tsunami height estimation. We developed the logic-tree models for local tsunami sources around Japan and for distant tsunami sources along the South American subduction zones. Logic-trees were made for tsunami source zones, size and frequency of tsunamigenic earthquakes, fault models, and standard error of estimated tsunami heights. Numerical simulation rather than empirical relation was used for estimating the median tsunami heights. Weights of discrete branches that represent alternative hypotheses and interpretations were determined by the questionnaire survey for tsunami and earthquake experts, whereas those representing the error of estimated value were determined on the basis of historical data. Examples of tsunami hazard curves were illustrated for the coastal sites, and uncertainty in the tsunami hazard was displayed by 5-, 16-, 50-, 84- and 95-percentile and mean hazard curves.     

Conceptual examination of climate–soil controls upon rainfall partitioning in an open-fractured soil II: Response to a population of storms

A simple two-domain bucket model of fractured soil was coupled with a stochastic model of rainfall variability, in order to investigate the climate and soil controls upon the stochastic properties of the triggering of fracture flow and surface runoff, and the partitioning of rainfall between the matrix and fracture domains and surface runoff. Conventionally, soils are regarded as time domain filters between rainfall and hydrological response. This investigation highlights an additional type of threshold filtering especially important in understanding the infiltration behaviour of fractured soils, for which an event-based characterisation of rainfall in modelling is crucial. A priori-definable indices were derived which are capable of describing elements of this threshold filtering, by allowing the statistical properties of fracture flow- and surface runoff-triggering storms (i.e., mean and variance of storm duration, intensity and effective inter-storm period, as well as cumulative partitioning of rainfall), to be inferred directly from average storm and soil properties. Using these indices, the long-term response of fractured soils, including the long-term hydrological importance of fractures, can be estimated without simulation.