共查询到20条相似文献，搜索用时 31 毫秒
1.
K. Chaouche P. Hubert G. Lang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(5):342-357
The purpose of this paper is to present a graphical method to characterise the nature of a distribution (exponential or algebraic).
In the algebraic case, this statistical tool provides an estimation procedure of the parameter characterising the decrease
of the survival function. The realizations of the random variable under study being available in the form of time series,
this method is based on the relationship between the duration of exceeding an intensity threshold and the accumulation of
the realizations of the random variable during this length of time. The behaviour of the duration-accumulation graphs (when
the threshold of reference increases indefinitely) results in a function, the limit of which only depends on the parameter
characterising the algebraic decrease of the probability distribution. The estimate of this parameter is biased but can be
corrected effectively by numerical methods. We applied this method to two rainfall series differing by their geographical
origin (Dédougou in Burkina Faso and a station on the Island of La Réunion) and their time step (respectively 1 day and 76
seconds). For both of them, the behaviour of tail distributions is shown to be algebraic and the values of the parameter characterizing
the algebraic decrease of the probability distribution of the two series are very close. This would tend to justify the assumption
of a multifractal nature for these series.
This work was achieved as part of the National Programme of Research in Hydrology of the INSU (project 99 PNRH 27). The authors
are grateful to A. Barcello for providing them the data of the Island of La Réunion Island. 相似文献
2.
Estimating the probability of river channel adjustment 总被引：1，自引：0，他引：1
Peter W. Downs 《地球表面变化过程与地形》1995,20(7):687-705
River channels respond not only to natural external controls, and natural controls internal to individual drainage basins, but also to the influence of human activity. Although many site-specific instances of change have been documented, the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment, or their relative sensitivity to drainage basin controls. Data obtained from the Thames Basin, southeast England, are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics. Adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment. This approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty. Four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey. In comparison, it is shown that laterally migrating river channels are the most common ‘natural’ channel type in the Thames Basin, and their probability of occurrence rises to 71 per cent in sand/gravel environments. In channels regulated by low weirs, deposition is the most likely channel activity where gradients are lower than 0·0040, whilst above this threshold the majority of channels are morphologically inactive. In urban channels, many of which are also lined by concrete, the likelihood of obtaining a stable channel is mostly in excess of 80 per cent. In channels straightened during this century, deposition is most likely in gradients below 0·0050, whereas erosional enlargement is most probable above this value. In channels which were initially channelized prior to this century, deposition gives way to stability at a threshold gradient of 0·0080. 相似文献
3.
The probability distributions of field differences x()=x(t+)-x(t), where the variable x(t) may denote any solar wind scalar field or vector field component at time t, have been calculated from time series of Helios data obtained in 1976 at heliocentric distances near 0.3 AU. It is found that for comparatively long time lag , ranging from a few hours to 1 day, the differences are normally distributed according to a Gaussian. For shorter time lags, of less than ten minutes, significant changes in shape are observed. The distributions are often spikier and narrower than the equivalent Gaussian distribution with the same standard deviation, and they are enhanced for large, reduced for intermediate and enhanced for very small values of x. This result is in accordance with fluid observations and numerical simulations. Hence statistical properties are dominated at small scale by large fluctuation amplitudes that are sparsely distributed, which is direct evidence for spatial intermittency of the fluctuations. This is in agreement with results from earlier analyses of the structure functions of x. The non-Gaussian features are differently developed for the various types of fluctuations. The relevance of these observations to the interpretation and understanding of the nature of solar wind magnetohydrodynamic (MHD) turbulence is pointed out, and contact is made with existing theoretical concepts of intermittency in fluid turbulence. 相似文献
4.
Influence of weak trends on exceedance probability 总被引：1，自引：0，他引：1
Studying the hypothetical case of a trend superimposed on a random stationary variable, we highlight the strong influence
of possible non-stationarities on exceedance probability. After a general outline, the subject is analytically developed using
the Gumbel distribution, emphasizing the quick increase of the exceedance probability over time in the presence of weak rising
trends, and its sensitive underestimation where the non-stationarity goes unnoticed or is considered negligible. Finally the
work is applied to hydrological series of rainfall and river flow.
Received: March 27, 1997 相似文献
5.
Yung-Chia Hsu Yeou-Koung Tung Jan-Tai Kuo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(1):35-49
This study develops a probability-based methodology to evaluate dam overtopping probability that accounts for the uncertainties
arising from wind speed and peak flood. A wind speed frequency model and flood frequency analysis, including various distribution
types and uncertainties in their parameters, are presented. Furthermore, dam overtopping probabilities based on monthly maximum
(MMax) series models are compared with those of the annual maximum (AMax) series models. An efficient sampling scheme, which
is a combination of importance sampling (IS) and Latin Hypercube sampling (LHS) methods, is proposed to generate samples of
peak flow rate and wind speed especially for rare events. Reservoir routing, which incorporates operation rules, wind setup,
and run-up, is used to evaluate dam overtopping probability. 相似文献
6.
A. Porporato L. Ridolfi 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(1):1-14
Studying the hypothetical case of a trend superimposed on a random stationary variable, we highlight the strong influence
of possible non-stationarities on exceedance probability. After a general outline, the subject is analytically developed using
the Gumbel distribution, emphasizing the quick increase of the exceedance probability over time in the presence of weak rising
trends, and its sensitive underestimation where the non-stationarity goes unnoticed or is considered negligible. Finally the
work is applied to hydrological series of rainfall and river flow.
Received: March 27, 1997 相似文献
7.
Q.J. Wang 《Journal of Hydrology》1990,120(1-4):115-124
Unbiased estimators of probability weighted moments (PWM) and partial probability weighted moments (PPWM) from systematic and historical flood information are derived. Applications are made to estimating parameters and quantiles of the generalized extreme value (GEV) distribution. The effect of lower bound censoring, which might be deliberately introduced in practice, is also considered. 相似文献
8.
9.
Because of the ubiquitous nature of anthropogenic nitrate (NO3(-)) in many parts of the world, determining background concentrations of NO3(-) in shallow ground water from natural sources is probably impossible in most environments. Present-day background must now include diffuse sources of NO3(-) such as disruption of soils and oxidation of organic matter, and atmospheric inputs from products of combustion and evaporation of ammonia from fertilizer and livestock waste. Anomalies can be defined as NO3(-) derived from nitrogen (N) inputs to the environment from anthropogenic activities, including synthetic fertilizers, livestock waste, and septic effluent. Cumulative probability graphs were used to identify threshold concentrations separating background and anomalous NO(3)-N concentrations and to assist in the determination of sources of N contamination for 232 spring water samples and 200 well water samples from karst aquifers. Thresholds were 0.4, 2.5, and 6.7 mg/L for spring water samples, and 0.1, 2.1, and 17 mg/L for well water samples. The 0.4 and 0.1 mg/L values are assumed to represent thresholds for present-day precipitation. Thresholds at 2.5 and 2.1 mg/L are interpreted to represent present-day background concentrations of NO(3)-N. The population of spring water samples with concentrations between 2.5 and 6.7 mg/L represents an amalgam of all sources of NO3(-) in the ground water basins that feed each spring; concentrations > 6.7 mg/L were typically samples collected soon after springtime application of synthetic fertilizer. The 17 mg/L threshold (adjusted to 15 mg/L) for well water samples is interpreted as the level above which livestock wastes dominate the N sources. 相似文献
10.
Resistivity anomaly imaging by probability tomography 总被引：10，自引：0，他引：10
Probability tomography is a new concept reflecting the inherently uncertain nature of any geophysical interpretation. The rationale of the new procedure is based on the fact that a measurable anomalous field, representing the response of a buried feature to a physical stimulation, can be approximated by a set of partial anomaly source contributions. These may be given a multiplicity of configurations to generate cumulative responses, which are all compatible with the observed data within the accuracy of measurement. The purpose of the new imaging procedure is the design of an occurrence probability space of elementary anomaly sources, located anywhere inside an explored underground volume. In geoelectrics, the decomposition is made within a regular resistivity lattice, using the Frechet derivatives of the electric potential weighted by resistivity difference coefficients. The typical tomography is a diffuse image of the resistivity difference probability pattern, that is quite different from the usual modelled geometry derived from standard inversion. 相似文献
11.
12.
Jeen-Shang Lin 《地震工程与结构动力学》1990,19(6):911-923
A method for constructing seismic slope failure probability matrices is presented. The core of the method is a probabilistic sliding block model which allows for systematic incorporation of the uncertainties associated with both the ground excitation and the strength of the slope materials. The extent of damage to a slope is defined in terms of the magnitude of the earthquake-induced permanent displacement. The intensity of the ground shaking is characterized by a peak ground acceleration as well as an earthquake magnitude, and the possible scatter in the ground motion details is included through the use of an equivalent stationary motion model. After the effects of essential contributing factors are discussed, regional seismic slope failure probability matrices are presented for general applications. 相似文献
13.
太湖水体的后向散射概率 总被引：1，自引：0，他引：1
假设2004年10月太湖水体的吸收系数和遥感反射比的测量误差为0,利用生物光学模型,通过优化算法,在光学深水区模拟获得水体的后向散射系数,然后通过后向散射概率和颗粒物后向散射系数之间的定量关系,获得水体中可能真实的颗粒物后向散射概率结果表明,太湖水体的颗粒物后向散射概率不是一个定值,可以表示为波长的二次函数,在442、488、532、589、676和852nm处分别为0.017、0.017、0.027、0.033、0.054和0.094,均值为0.041,标准偏差为0.030。 相似文献
14.
应用金学申、王晓青等推广的以时空概率增益模型为基础的综合预测模型,选取东南沿海地震带区域,分别计算了地震活动的时间和空间上的地震概率增益,并对其中的概率增益等参数进行分析,结果表明本区域的未来控震构造是北东向活动断裂带,未来3年本区域发生5级以上的地震概率较小。 相似文献
15.
Wout M. van Dijk Dick R. Mastbergen Geeralt A. van den Ham Jasper R. F. W. Leuven Maarten G. Kleinhans 《地球表面变化过程与地形》2018,43(11):2342-2357
Channel bank failure, and collapses of shoal margins and beaches due to flow slides, have been recorded in Dutch estuaries for the past 200 years but have hardly been recognized elsewhere. Current predictions lack forecasting capabilities, because they were validated and calibrated for historic data of cross‐sections in specific systems, allowing local hindcast rather than location and probability forecasting. The objectives of this study were to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are, such that we can predict their occurrence. We identified shoal margin collapses, generally completely submerged, from bathymetry data by analyzing digital elevation models of difference of the Western Scheldt for the period 1959–2015. We used the bathymetry data to determine the conditions for occurrence, specifically to obtain slope height and angle, and applied these variables in a shoal margin collapse predictor. We found 299 collapses along 300 km of shoal margin boundaries over 56 years, meaning that more than five collapses occur on average per year. The average shoal margin collapse body is well approximated by a 1/3 ellipsoid shape, covers on average an area of 34 000 m2 and has an average volume of 100 000 m3. Shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross‐section of the entire estuary, and occur most frequently where lateral shoal margin displacement is low. A receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well. We conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the Western Scheldt, and likely locations are at laterally relatively stable shoal margins. This provides hypotheses aiding the recognition of these features in sandy estuaries worldwide. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
16.
通过对测震学各单项指标的预测效能调研，为进一步提取前兆信息，选择了7项测震学指标：频次、地震蠕变、6值、缺震、η值、GL值和调制比，进行综合概率分析。7项指标对关注地区的全时空扫描并考虑了空间单元异常与中强震地点对应的模糊关系，得到指标在各空间单元异常后发生中强震的条件概率。根据历史上每个单项指标的预报效能求计算综合概率时的指标权重，按贝叶斯定律得到相应不同指标在不同时间窗和不同空间单元时中强震发生的加权综合概率。计算结果（1970年以来）表明，对华北地区和川滇地区这一综合概率方法预测效能的R值评估超过0.5。 相似文献
17.
工程结构地震破坏概率矩阵分析 总被引：3，自引：0，他引：3
本文提出了一种计算工程结构地震坡坏概率矩阵的方法，建立了地震地面运动模型和结构分析模型，对结构进行了随机地震反应分析，并获得了结构随机分应的统计量，进而采用双参数的结构破坏模型，给出了教育处结构地震破坏概率的表达式，利用此方法计算了一座按8度要求设计的钢筋混凝土框架型，给出了计算结构地震坡坏概率的表达式，利用此方法计算了一座按8度要求的钢筋混凝土框架结构的地震破坏概率矩阵，本文提出了方法可以在确定抗震设防标准和进行震害预测时采用。 相似文献
18.
概率地震危险性分析是对相关区域地震活动水平的估计,是量化地震危险性的有效手段。基于泊松分布模型获得山西地区背景地震概率,结合每个单项方法预测效能获取的指标权重,采用综合概率法得到山西地区基于多种单项预测方法的地震综合概率模型。对 1985年以来山西地区 MS ≥ 5.0地震进行回溯性检验,结果表明：异常点受控于统一应力场,震前各类（包括测震、形变、电磁以及流体学科）预测指标均存在且表现出准同步性;震级大小与异常数量呈一定正相关性,震级越大,异常指标越多,综合概率值越大。 相似文献
19.
Steve W. Lyon Arthur J. Lembo Jr. M. Todd Walter Tammo S. Steenhuis 《Advances in water resources》2006
In humid, well-vegetated areas, such as in the northeastern US, runoff is most commonly generated from relatively small portions of the landscape becoming completely saturated, however, little is known about the spatial and temporal behavior of these saturated regions. Indicator kriging provides a way to use traditional water table data to quantify probability of saturation to evaluate predicted spatial distributions of runoff generation risk, especially for the new generation of water quality models incorporating saturation excess runoff theory. When spatial measurements of a variable are transformed to binary indicators (i.e., 1 if above a given threshold value and 0 if below) and the resulting indicator semivariogram is modeled, indicator kriging produces the probability of the measured variable to exceed the threshold value. Indicator kriging gives quantified probability of saturation or, consistent with saturation excess runoff theory, runoff generation risk with depth to water table as the variable and the threshold set near the soil surface. The probability of saturation for a 120 m × 180 m hillslope based upon 43 measurements of depth to water table is investigated with indicator semivariograms for six storm events. The indicator semivariograms show high spatial structure in saturated regions with large antecedent rainfall conditions. The temporal structure of the data is used to generate interpolated (soft) data to supplement measured (hard) data. This improved the spatial structure of the indicator semivariograms for lower antecedent rainfall conditions. Probability of saturation was evaluated through indicator kriging incorporating soft data showing, based on this preliminary study, highly connected regions of saturation as expected for the wet season (April through May) in the Catskill Mountain region of New York State. Supplementation of hard data with soft data incorporates physical hydrology of the hillslope to capture significant patterns not available when using hard data alone for indicator kriging. With the need for water quality models incorporating appropriate runoff generation risk estimates on the rise, this manner of data will lay the groundwork for future model evaluation and development. 相似文献
20.
At sites where a dense nonaqueous phase liquid (DNAPL) was spilled or released into the subsurface, estimates of the mass of DNAPL contained in the subsurface from core or monitoring well data, either in the nonaqueous or aqueous phase, can be highly uncertain because of the erratic distribution of the DNAPL due to geologic heterogeneity. In this paper, a multiphase compositional model is applied to simulate, in detail, the DNAPL saturations and aqueous-phase plume migration in a highly characterized, heterogeneous glaciofluvial aquifer, the permeability and porosity data of which were collected by researchers at the University of Tübingen, Germany. The DNAPL saturation distribution and the aqueous-phase contaminant mole fractions are then reconstructed by sampling the data from the forward simulation results using two alternate approaches, each with different degrees of sampling conditioning. To reconstruct the DNAPL source zone architecture, the aqueous-phase plume configuration, and the contaminant mass in each phase, one method employs the novel transition probability/Markov chain approach (TP/MC), while the other involves a traditional variogram analysis of the sampled data followed by ordinary kriging. The TP/MC method is typically used for facies and/or hydraulic conductivity reconstruction, but here we explore the applicability of the TP/MC method for the reconstruction of DNAPL source zones and aqueous-phase plumes. The reconstructed geometry of the DNAPL source zone, the dissolved contaminant plume, and the estimated mass in each phase are compared using the two different geostatistical modeling approaches and for various degrees of data sampling from the results of the forward simulation. It is demonstrated that the TP/MC modeling technique is robust and accurate and is a preferable alternative compared to ordinary kriging for the reconstruction of DNAPL saturation patterns and dissolved-phase contaminant plumes. 相似文献