Forward model nonlinearity versus inverse model nonlinearity

The issue of concern is the impact of forward model nonlinearity on the nonlinearity of the inverse model. The question posed is, “Does increased nonlinearity in the head solution (forward model) always result in increased nonlinearity in the inverse solution (estimation of hydraulic conductivity)?” It is shown that the two nonlinearities are separate, and it is not universally true that increased forward model nonlinearity increases inverse model nonlinearity.     

Combining climate model output via model correlations

In climate science, collections of climate model output, usually referred to as ensembles, are commonly used devices to study uncertainty in climate model experiments. The ensemble members may reflect variation in initial conditions, different physics implementations, or even entirely different climate models. However, there is a need to deliver a unified product based on the ensemble members that reflects the information contained in whole of the ensemble. We propose a technique for creating linear combinations of ensemble members where the weights are constructed from estimates of variation and correlation both within and between ensemble members. At the heart of this approach is a Bayesian hierarchical model that allows for estimation of the correlation between ensemble members as well as the study of the impact of uncertainty in the parameter estimates of the hierarchical model on the weights. The approach is demonstrated on an ensemble of regional climate model (RCM) output.     

基于褶积模型的地球物理反演模型增强

地球物理数据在采集和处理过程中,由于存在噪声、模型误差、以及数据离散化误差等系统误差,导致了异常体边界模糊和模型分辨率降低等一些不可避免的不良系统退化效应的产生.本文提出了一种新的地球物理反演模型增强方法,通过消除反演估计模型中的系统误差,压制模型中的不良系统退化效应,增强反演模型的分辨率.文章从理论上分析了数据中存在的系统误差对模型求解的影响,提出了一个新的系统误差褶积退化模型,并根据该模型提出了一种基于混合范数总变分正则化的盲反褶积模型增强算法.最后,文章通过1D线性反演增强试验和2D大地电磁反演增强试验,验证了所提出的地球物理系统退化模型的正确性,以及盲反褶积增强算法的有效性.试验结果表明,方法可以有效地提高反演参数模型的分辨率.     

Patuxent landscape model: 1. Hydrological model development

We developed a spatially explicit, process-based model of the 2352 km² Patuxent river watershed in Maryland, and its subwatersheds to integrate data and knowledge over several spatial, temporal and complexity scales, and to serve as an aid to regional management. The model was developed using the Library of Hydro-Ecological Modules (LHEM, http://giee.uvm.edu/LHEM), which was designed to create flexible landscape model structures that can be easily modified and extended to suit the requirements of a variety of goals and case studies. The LHEM includes modules that simulate various aspects of ecosystem dynamics. In this paper we consider modules that represent the physical conditions in the environment (climatic factors, geoporphology), and hydrologic processes, both locally and spatially. Where possible the modules are formulated as Stella(R) models, spatial transport processes are presented as C++ code.     

Developing land use scenario dynamics model by the integration of system dynamics model and cellular automata model

Models of land use change are useful tools for un-derstanding the analysis of the cause and conse-quences of land use changes, assessing the impacts of land use system on ecological system and supporting land use planning and policy[1,2]. Modeling land use scenario changes and its potential impacts on the structure and function of the ecosystem in the typical regions are regarded as one of the good ways to un-derstand the interactive mechanism between land use system and ecological system[3―10…     

基于Park三参数模型的剪切滞变模型

针对深梁、短柱和剪力墙等剪跨比较小的构件在结构非线性分析中需要考虑剪切效应的情况,在Park三参数滞变模型的基础上,参考大量文献后,建议了短柱、剪力墙和核心筒三种构件的剪力-剪切变形曲线本构关系特征点的参数取值,给出了剪跨比较小构件的剪切滞变模型。采用该模型分别对短柱、剪力墙和核心筒三个试验模型进行了模拟和分析,分析结果与试验结果的对比表明,所给模型可较好地模拟试件的剪切效应及实际抗剪承载力水平。该模型的建立可为结构非线性分析中有效考虑剪切效应提供参考。     

A complementary relationship evaporation model referring to the Granger model and the advection–aridity model

A complementary relationship evaporation model has been proposed and verified based on evaluations of the advection–aridity model and the Granger's complementary relationship model (Granger model) in dimensionless forms. Normalized by Penman potential evaporation, the Granger model and the advection–aridity model have been transformed into similar dimensionless forms. Evaporation ratio (ratio of actual evaporation to Penman potential evaporation) has been expressed as a function of dimensionless variable based on radiation and atmospheric conditions. Similar dimensionless variables for the different functions have been used in the two models. By referring to the dimensionless variable from the advection–aridity model and the function from the Granger model, a new model to estimate actual evaporation was proposed. The performance of the new model has been validated by the observed data from four sites under different land covers. The new model is an enhanced Granger model with better evaporation prediction over the aforementioned different land covers. It also offers more stable optimized parameters in a grassland site than the Granger model. The new model somewhat approximates the advection–aridity model under neither too wet nor too dry conditions, but without its system bias. Copyright © 2011 John Wiley & Sons, Ltd.     

A synthetic Earth gravity model based on a topographic-isostatic model

The Earth??s gravity field is related to the topographic potential in medium and higher degrees, which is isostatically compensated. Hence, the topographic-isostatic (TI) data are indispensable for extending an available Earth Gravitational Model (EGM) to higher degrees. Here we use TI harmonic coefficients to construct a Synthetic Earth Gravitational Model (SEGM) to extend the EGMs to higher degrees. To achieve a high-quality SEGM, a global geopotential model (EGM96) is used to describe the low degrees, whereas the medium and high degrees are obtained from the TI or topographic potential. This study differes from others in that it uses a new gravimetric-isostatic model for determining the TI potential. We test different alternatives based on TI or only topographic data to determine the SEGM. Although the topography is isostatically compensated only to about degree 40?C60, our study shows that using a compensation model improves the SEGM in comparison with using only topographic data for higher degree harmonics. This is because the TI data better adjust the applied Butterworth filter, which bridges the known EGM and the new high-degree potential field than the topographic data alone.     

动力UH模型

针对砂土在动力荷载作用下所表现出的应力诱导各向异性,以改进后的UH超固结土模型为基础,采用旋转硬化规则将其扩展为可考虑与砂土应力应变关系的动本构模型。主要改进有3方面:(1)将形状固定的椭圆屈服面改变为可变屈服面,椭圆的形状由β来刻画,而β本身是椭圆旋转轴的大小,表示应力诱导各向异性程度的大小;(2)引入旋转硬化规则,使椭圆屈服面可围绕原点旋转以反映反向加载条件下的本构响应;(3)对统一硬化参数进行了修正,首先对潜在强度公式增加了一个参数α用来调节超固结应力比参数R对于潜在强度值的影响,其次针对应力诱导各向异性建立起能反映旋转硬化与等向硬化相协调的扩展统一硬化参数。模型预测与试验结果的对比以及有限元模拟表明:提出的动力统一硬化(DUH)模型能够简单、合理的描述与砂土在动力载荷下的本构关系,验证了所提模型的合理性。     

A newF-layer model

Summary The model originally constructed for theF1-layer is adapted to enable an investigation of both theF-layers. Essential premises are: The ionization of a single constituent of atmosphere by monochromatic radiation. A positive temperature gradient in theFl-region, a temperature—independent from height—in theF2-region and a negative temperature gradient above the height of theF2-electron-peak; furthermore during the daytime strong heating in theF2-region. It is further assumed that the rate of electron loss in theF1-layer is proportional to the square of the density of the electrons, and in theF2-layer is in simple proportion to this density. It is also assumed that this electron loss stands in proportion to the powerk of the pressurep, and to the powern of the absolute temperatureT, as assumed in the originalF1-layer model.The above mentioned assumption as to temperature conditions are essential to an understanding of the transition from static to dynamic conditions observed in theF2-layer. During the night and in the morning theF2-layer can be treated as a static problem, movement of air-masses being of no great importance. Later in the day however an labile stratification of air-masses gives rise to such movement that theF2-layer can only be handled as a dynamic problem, particular attention being paid to the movement of the air.Numerous observational data are referred to in order to prove the practicability of the new model and, with the help of this model, to justify new assertions. It has been possible for example, to calculate the yearly temperature variation at a constant level in theF1-layer.A critical report upon the models published recently by other authors concludes this paper.

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Zusammenfassung Das seinerzeit nur für dieF1-Schicht aufgestellte Modell wird so erweitert, daß eine Deutung beiderF-Schichten möglich wird. Wesentliche Voraussetzungen sind: Ionisierung eines einzigen Bestandteiles der Luft durch eine monochromatische Strahlung. Ein positiver Temperaturgradient im Bereich derF1-Schicht, eine höhen-unabhängige Temperatur im Bereich derF2-Schicht und ein negativer Temperaturgradient oberhalb des Ionisationsmaximum, derF2-Schicht. Weiters wird vorausgesetzt, daß der Elektronenvernichtungsprozeß in derF1-Schicht dem Quadrat der Elektronendichte proportional sei, in derF2-Schicht soll er dagegen der Elektronendichte einfach proportional sein. Eine Abhängigkeit dieses Prozesses von derk-ten Potenz des Druckes,p und von dern-ten Potenz der absoluten TemperaturT wird hier vom ursprünglichenF1-Schicht-Modell übernommen.Erst die genannten Annahmen über die Temperaturverhältnisse machen den beobachteten Übergang von statischen zu dynamischen Verhältnissen in derF2-Schicht verständlich. Während der Nacht und am Morgen bis in die ersten Vormittagsstunden kann dieF2-Schicht als statisches Problem behandelt werden, die Bewegungsvorgänge der Luftmassen spielen eine nur untergeordnete Rolle. Darnach aber ruft eine labile Schichtung der Luftmassen kräftige Luftbewegungen hervor, sodaß dieF2-Schicht nur mehr als dynamisches Problem mit besonderer Berücksichtigung von Luftmassenverschiebungen behandelt werden kann.Zahlreiche Beobachtungsdaten werden herangezogen, um die Anwendbarkeit des neuen Modells zu beweisen und um mit Hilfe des Modells zu neuen Aussagen zu gelangen. Es gelingt so z. B., den Jahresgang der Temperatur in einem konstant gehaltenen Druckniveau derF1-Schicht anzugeben.Eine kritische Betrachtung der Modelle, die in letzterer Zeit von anderen Autoren veröffentlicht wurden, beschließt die Arbeit.

     

Blaney-Morin-Nigeria evapotranspiration model

An evapotranspiration model which parallels that proposed earlier by Blaney and Morin has been developed for application in Nigeria. The model, designated as the Blaney-Morin-Nigeria evapotranspiration model, predicts potential evapotranspiration with accuracy and consistency that are better than the Penman model, under Nigerian conditions. It is suggested that the Blaney-Morin evapotranspiration concept may have similar potential elsewhere when given specific form with appropriate constants derived to reflect climatic peculiarities.     

Bayesian model averaging assessment on groundwater management under model structure uncertainty

This study introduces Bayesian model averaging (BMA) to deal with model structure uncertainty in groundwater management decisions. A robust optimized policy should take into account model parameter uncertainty as well as uncertainty in imprecise model structure. Due to a limited amount of groundwater head data and hydraulic conductivity data, multiple simulation models are developed based on different head boundary condition values and semivariogram models of hydraulic conductivity. Instead of selecting the best simulation model, a variance-window-based BMA method is introduced to the management model to utilize all simulation models to predict chloride concentration. Given different semivariogram models, the spatially correlated hydraulic conductivity distributions are estimated by the generalized parameterization (GP) method that combines the Voronoi zones and the ordinary kriging (OK) estimates. The model weights of BMA are estimated by the Bayesian information criterion (BIC) and the variance window in the maximum likelihood estimation. The simulation models are then weighted to predict chloride concentrations within the constraints of the management model. The methodology is implemented to manage saltwater intrusion in the “1,500-foot” sand aquifer in the Baton Rouge area, Louisiana. The management model aims to obtain optimal joint operations of the hydraulic barrier system and the saltwater extraction system to mitigate saltwater intrusion. A genetic algorithm (GA) is used to obtain the optimal injection and extraction policies. Using the BMA predictions, higher injection rates and pumping rates are needed to cover more constraint violations, which do not occur if a single best model is used.     

An analytical study on turbulence with mixed-flow model and two-phase model

Suspended sediment is carried by turbulent water flows in rivers.Traditional sediment-laden flow analysis treats the suspension as a mixed liquid,and recent two-phase flow model enables separate velocity measurement of the two coupling phases.A simplified theoretical analysis was presented to discuss the differences between the two models in reporting turbulence intensity in experimental research.The turbulence intensity of the mixture is lower than the weighted average of those of the two phases in mixed-flow experiments.The mixture’s turbulence intensity becomes higher than the average of the two phases in two-phase experiments due to the presence of velocity lag.The same set of data may lead to either an underestimation or an overestimation of actual turbulence levels when different models are used.     

基于多植物生长模式的SWAT模型的修正与有效性初探

以农林系统的非点源污染模拟为目标,通过研究建立变化密度及多种类混杂的森林生长模型,修正了SWAT模型采用平均森林植被密度和单一植物生长模式估算生物累积量的问题,并建立了与之相适应的森林优势组份丰度遥感反演模型、叶面积指数和消光系数遥感反演模型以获取森林生长模型的相关参数.同时,根据间作套种下的辐射能利用Keating方程,引入间作套种指数变量,修正SWAT原有的单一生物量日积累模型,探讨了作物复种指数、间作套种指数遥感反演方法和以此为基础的作物间作套种生长模型.以亚热带季风湿润区红壤背景下的鄱阳湖流域子流域梅江流域为试验区,以野外实测数据为基础,探讨修正SWAT模型的有效性.结果表明:修正后的SWAT模型与原始SWAT模型相比,在模拟流量和营养盐负荷方面,得到了较好的改善.在模拟流量方面,有效性提高了7.8%,流量峰值的模拟也得到了改善,能更好地反映地表蓄流方面的实际情况;在模拟营养盐负荷方面,有效性提高了6.4%(总磷)和6.1%(总氮).     

顾及次优噪声模型的GNSS坐标时间序列噪声模型选择

在全球导航卫星系统（Global Navigation Satellite System,GNSS）坐标时间序列噪声建模领域,选择合适的噪声模型对GNSS坐标时间序列的速度信号提取具有重要价值.长期以来,研究者专注于建立最优噪声模型来描述GNSS坐标时间序列中的噪声成分,却往往直接忽略与最优噪声模型性能接近的次优噪声模型.本文选用8种常见的噪声模型,使用极大似然估计法（Maximum Likelihood Estimate,MLE）估计模型参数,以赤池信息量准则（Akaike information criterion,AIC）作为评价准则来选取噪声模型.实验数据采用中国区域12个国际GNSS服务（International GNSS Service,IGS）基准站36个坐标分量及全球范围内50个IGS基准站150个坐标分量的坐标时间序列.结果表明,超过半数的测站坐标分量上存在与最优噪声模型性能接近的次优噪声模型.在此基础上中国区域的IGS站,在东方向有14%的次优噪声模型拥有比最优噪声模型数值更大的速度不确定度,在北方向和垂直方向,这一值分别为33%和63%.而对于全球范围的IGS站,这一值分别为31%、39%和48%.因此在GNSS坐标时间序列噪声模型选择过程中,充分考虑与最优噪声模型性能接近的次优噪声模型有助于获得到更保守的估计结果.

     

Infiltration model in sloping layered soils and guidelines for model parameter estimation

A Green-Ampt type model for sloping layered soils (GASLS) was developed to investigate infiltration processes. We introduced a factor c, which is the same for all layers and represents the ratio of effective hydraulic conductivity over saturated hydraulic conductivity. Guidelines to estimate the factor c were established based on 234 scenarios under various conditions. The model with the estimated factor c can describe infiltration processes better than that with c = 1. For fine soils, or layered formations with finer soils on the top, c is smaller than 1. The factor c for coarse soils, or layer formations with coarse soils on the top is close to 1. Comparison with laboratory experiments on a sloping surface indicated that the GASLS model with a slope factor that is adjusted by the sine of the slope angle can represent the sloping surface effects. The GASLS model can incorporate any slope factor.     

Sensitivity analyses of a distributed catchment model to verify the model structure

Sensitivity analyses are valuable tools for identifying important model parameters, testing the model conceptualization, and improving the model structure. They help to apply the model efficiently and to enable a focussed planning of future research and field measurement. Two different methods were used for sensitivity analyses of the complex process-oriented model TAC^D (tracer aided catchment model, distributed) that was applied to the meso-scale Brugga basin (40 km²) and the sub-basin St Wilhelmer Talbach (15.2 km²). Five simulations periods were investigated: two summer events, two snow melt induced events and one summer low flow period. The model was applied using 400 different parameter sets, which were generated by Monte Carlo simulations using latin hypercube sampling. The regional sensitivity analysis (RSA) allowed determining the most significant parameters for the complete simulation periods using a graphical method. The results of the regression-based sensitivity analysis were more detailed and complex. The temporal variability of the simulation sensitivity could be observed continuously and the significance of the parameters could be determined in a quantitative way. A dependency of the simulation sensitivity on initial- and boundary conditions and the temporal and spatial variability of the sensitivity to some model parameters was revealed by the regression-based sensitivity analysis. Thus, the difficulty of transferring the results to different time periods or model applications in other catchments became obvious. The analysis of the temporal course of the simulation sensitivity to parameter values in conjunction with simulated and measured additional data sets (precipitation, temperature, reservoir volumes etc.) gave further insight into the internal model behaviour and demonstrated the plausibility of the model structure and process conceptionalizations.     

Preliminary reference Earth model

A large data set consisting of about 1000 normal mode periods, 500 summary travel time observations, 100 normal mode Q values, mass and moment of inertia have been inverted to obtain the radial distribution of elastic properties, Q values and density in the Earth's interior. The data set was supplemented with a special study of 12 years of ISC phase data which yielded an additional 1.75 × 10⁶ travel time observations for P and S waves. In order to obtain satisfactory agreement with the entire data set we were required to take into account anelastic dispersion. The introduction of transverse isotropy into the outer 220 km of the mantle was required in order to satisfy the shorter period fundamental toroidal and spheroidal modes. This anisotropy also improved the fit of the larger data set. The horizontal and vertical velocities in the upper mantle differ by 2–4%, both for P and S waves. The mantle below 220 km is not required to be anisotropic. Mantle Rayleigh waves are surprisingly sensitive to compressional velocity in the upper mantle. High S_n velocities, low P_n velocities and a pronounced low-velocity zone are features of most global inversion models that are suppressed when anisotropy is allowed for in the inversion.The Preliminary Reference Earth Model, PREM, and auxiliary tables showing fits to the data are presented.     

Ray path-length-dependent slowness model

By introducing a new parameter, slowness deviation, a ray-path-length-dependent slowness model has been previously developed. Synthetic tests indicate that for a horizontal layered slowness structure, the new model gives a good estimate of the weighted average slowness of a ray when the rays considered cover a small range of take-off angles. When the rays considered cover a large range of take-off angles, the new model gives good estimates of the weighted average slowness for the long rays, but large errors still remain for the short rays.