基于粒子群算法的瑞雷波频散曲线反演研究

瑞雷波频散曲线反演的本质是对目标函数求极值的过程.传统的线性局部反演算法容易陷入局部极小值,增加了反演结果的不确定性.粒子群算法作为一种全局非线性优化手段,能够保证各搜索空间内局部寻优的同时,逼近全局最优,保证迭代反演的收敛性.建立含软夹层型地层模型,正演计算得到理论频散曲线,采用粒子群算法反演得到的横波速度与模型高度吻合.同时,在理论频散曲线中加入10%的高斯白噪声,粒子群算法的反演结果仍然具有很好的可靠程度.通过对实测频散曲线的反演表明:粒子群算法在含软夹层型地层的横波速度探测中相对于最小二乘法优势明显,具有很高的应用价值.     

基于混沌-粒子群优化的磁法数据非线性反演方法

磁法反演属于非线性最优化问题,具有多变量、目标函数多极值、反演多解性等特点,因此,需要稳定的和高效的优化反演算法.粒子群优化已开始被用于地球物理反演计算,但是对于高维数、多峰值函数,粒子群的收敛精度不高,容易陷入局部极值.如果将混沌局部搜索和粒子群优化的优势相结合,通过将种群搜索过程对应为混沌轨道的遍历过程,可使标准粒子群优化的搜索过程具有避免陷入局部极小的能力.本文利用混沌-粒子群优化用于磁法反演计算.数据试验结果表明,该方法可以用于磁法数据的地球物理非线性反演,并且在一定程度上优于标准粒子群优化方法.     

含激电效应的航空瞬变电磁数据横向约束反演

受激电效应影响,航空瞬变电磁响应曲线经常出现异常快速衰减和符号反转现象,使用Cole-Cole模型的等效电阻率代替原模型实电阻率能很好的解释该现象,但由于激电多个参数的引入,使得反演多解性问题更加严重.本文基于Cole-Cole模型实现了航空瞬变电磁一维正演,采用横向约束反演同时计算激电参数及层厚,增加约束条件改善多解...     

基于交叉梯度耦合的大地电磁与地震走时资料三维联合反演

为了有效解决目前大地电磁和地震走时资料单方法反演结果一致性不好的问题,同时克服基于岩石不同物性参数间关系耦合约束联合反演的局限性,本文研究了基于交叉梯度耦合约束的大地电磁与地震走时资料的三维联合反演算法.以较为成熟的天然地震走时资料三维正反演和大地电磁三维正反演算法为基础,实现了具有共同的反演网格,以交叉梯度结构耦合约束,并能同时获得电阻率和速度模型的三维联合反演算法.分别利用单棱柱体模型和双棱柱体模型合成数据进行了联合反演试算.结果表明:无论是单棱柱体模型还是双棱柱体模型,联合反演结果比单独反演对异常体的空间形态都有更好的恢复,其中单棱柱体模型反演的异常体电阻率更接近于真实电阻率,双棱柱体模型的联合反演结果不仅消除了围岩的部分电阻率假异常,而且增强了对异常体深部速度结构特征的恢复程度.联合反演还能同时改善电阻率和速度反向变化异常体的单独反演结果,进一步证明交叉梯度耦合不依赖于岩石物性关系,而强调地下结构的相似性,具有更普遍的适用性.     

全空间条件下矿井瞬变电磁法粒子群优化反演研究

煤矿井下矿井瞬变电磁法(MTEM)探测中,电磁场呈全空间分布,全空间瞬变电磁反演是复杂的非线性问题,目前反演计算中全空间响应主要由半空间响应乘以全空间响应系数来得到,导致反演结果中顶板和底板异常(或前方和后方异常)叠加在一起难以分离,造成分辨率下降.论文提出采用粒子群优化算法(PSO)进行全空间MTEM反演,通过理论分析,在常规的粒子群算法基础上提出了一种新的进化公式改进策略,提高了粒子群算法的寻优能力.基于全空间瞬变电磁场理论,编写了粒子群算法反演程序,进行全空间条件下五层含巷道的复杂模型的反演计算.结合某矿井巷道顶板、底板岩层及断层含水性的探测实例,对实测数据进行反演计算和解释,探测结果得到钻探证实.研究表明,改进的粒子群优化算法对理论模型和实际资料的反演拟合程度较高,实现了矿井顶板、底板视电阻率异常的分离,提高了全空间瞬变电磁勘探资料的解释精度和分辨率.     

基于交叉梯度约束的电阻率法和背景噪声法三维联合反演研究

电阻率法和背景噪声法是通过获得地下介质的电阻率和速度参数的分布来探究地球内部物质分布的非均匀性特征,联合反演可以有效地发挥两种方法的优势,减小反演多解性.本文采用有限内存拟牛顿（L-BFGS）算法实现了电阻率法和背景噪声法的单方法三维反演,然后基于电阻率和速度模型结构耦合约束,采用交替迭代方式实现了电阻率法和背景噪声法的三维联合反演.通过设计规则体组合模型和不规则体组合模型进行理论模型合成数据三维反演试算,结果表明：联合反演可以获得同时满足数据拟合差和结构更为相似的速度-电阻率模型;联合反演可以压制背景噪声单方法反演出现的假异常,获得更精细的速度结构;联合反演获得的电阻率模型对倾斜异常体、高阻覆层下方异常体、圈闭的高/低阻体等边界信息有明显的提升,有效克服电阻率法单方法反演的局限,提高深部电阻率的分辨率.     

基于交叉梯度约束的电阻率法和背景噪声法三维联合反演研究

电阻率法和背景噪声法是通过获得地下介质的电阻率和速度参数的分布来探究地球内部物质分布的非均匀性特征,联合反演可以有效地发挥两种方法的优势,减小反演多解性.本文采用有限内存拟牛顿(L-BFGS)算法实现了电阻率法和背景噪声法的单方法三维反演,然后基于电阻率和速度模型结构耦合约束,采用交替迭代方式实现了电阻率法和背景噪声法的三维联合反演.通过设计规则体组合模型和不规则体组合模型进行理论模型合成数据三维反演试算,结果表明:联合反演可以获得同时满足数据拟合差和结构更为相似的速度-电阻率模型;联合反演可以压制背景噪声单方法反演出现的假异常,获得更精细的速度结构;联合反演获得的电阻率模型对倾斜异常体、高阻覆层下方异常体、圈闭的高/低阻体等边界信息有明显的提升,有效克服电阻率法单方法反演的局限,提高深部电阻率的分辨率.     

基于有限内存拟牛顿法的电阻率法三维主轴各向异性反演研究

基于各向同性假设的电阻率法三维正反演方法成熟并得到广泛应用.由于地下介质普遍存在电阻率各向异性,为提高反演精度,各向异性介质的三维正反演问题有待深入研究.本文将三维正演中总场分为一次场和二次场计算,二次场使用非结构网格有限单元法求解,基于有限内存拟牛顿法,系统研究了电阻率法三维主轴各向异性反演.通过设计低阻异常体与双异常体模型,利用地表、地井、井地与井间多种观测方式的合成数据进行了反演试算.反演结果表明：三维主轴各向异性反演能够可靠恢复异常体的位置与形状.与仅在地表采集数据的反演结果对比,地井、井地与井间多种观测数据的加入,反演结果能更好地恢复异常体的各向异性特征.证明了本文基于有限内存拟牛顿法电阻率三维反演方法的可行性与有效性.     

利用Cole-Cole模型组合得到SIP真参数的联合频谱最优化反演

利用Cole-Cole模型组合和稀释系数理论，可以描述测量得到的视复电阻率频谱与地下多个电性体SIP真参数之间的正演关系。本利用此正演关系进行反演试算，并比较了几种Cole-Cole模型反演方案的效果；提出固定极化目标体和围岩体的极化率同时反演其它各SIP真参数的反演方案。结果表明在固定极化率为真值时，利用此反演方案可以稳定、准确、快速地得出地下电性体SIP真参数。     

基于交叉梯度约束的重力、磁法和大地电磁三维联合反演

为了降低单一地球物理方法反演的多解性及受噪声的影响程度,本文围绕重力、磁法和大地电磁法开展了三维联合反演的研究.重、磁采用基于对数障碍法的正则化反演算法,大地电磁使用limited-memory BroydenFletcher-Goldfarb-Shanno(L-BFGS)反演算法,引入交叉梯度函数实现了三种物性结构的相互耦合,最终开发出一套重磁电三维联合反演算法,并实现MPI并行加速计算.通过理论模型算例验证了算法的准确性,结果表明:不论是单棱柱体模型还是组合棱柱体模型,联合反演结果相较单独反演对于异常体的空间形态刻画以及物性数值恢复具有较好的提升;单棱柱体模型算例使得异常体的物性参数(密度、磁化率和电阻率)更加接近于真实的物性参数;组合棱柱体模型的联合反演结果不仅仅消除了围岩物性参数的假异常,而且还增强了异常体边界结构的恢复程度.     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Earthquake Engineering and Engineering Vibration Aims And Scope

正This journal is established by the Institute of Engineering Mechanics(IEM),China Earthquake Administration,to promote scientific exchange between Chinese and foreign scientists and engineers so as to improve the theory and practice of earthquake hazards mitigation,preparedness,and recovery.To accomplish this purpose,the journal aims to attract a balanced number of papers between Chinese and     

Foreword

Destructive earthquakes have caused great damage in China and the United States and collapsing buildings havecaused many deaths and injuries. The field of earthquake engineering studies earthquake hazards, the occurrence ofearthquakes of various magnitudes, the nature of the ground shaking during an earthquake, the vibration of structuresduring earthquakes, the strengthening of existing structures and the design of new structures to be earthquake resistant,and finally, how to cope with earthquake damage and restore a city to normal functioning. Such efforts are in progressin both countries, but unfortunately, the language barrier interferes with the free flow of information between China andthe Untied States. It would be mutually beneficial if some means could be developed to promote the exchangeof information across the Pacific Ocean. This new journal has been established for this purpose and its success willbe an important step in promoting earthquake engineering in China and the United States.     

WORLD ASSOCIATION FOR SEDIMENTATION AND EROSION RESEARCH(WASER)

正President:Giampaolo Di Silvio,Italy Vice Presidents:Ulrich C.E.Zanke,Germany Zhao-yin Wang,China The World Association for Sedimentation and Erosion Research(WASER),inaugurated on Oct.19,2004,is an independent non-governmental,non-profit organization.The mission of WASER is to promote international co-operation on the study     

Enhancing remote sensing research on global change to improve our understanding on Earth system processes

正Global Change includes climate change and other environmental changes caused by the joint interaction among various layers of Earth. From the positive side, global change provides new opportunities to human and other living forms on Earth. In the meantime, it creates tremendous challenges and negative impact. At present, the negative impacts have reached all primary processes of the global ecosystem and every aspect of human society, especially causing degradation of the ecosystem. For instance, intensive deforestation causes decline of biodiversity; global warming causes sea level rise and increases     

Solute concentrations in the lower niger river and the source rock contribution

Water quality analyses for the Niger River for the 1980/81 hydrological year are presented. The samples were collected from the main river at Lokoja, and from two main tributaries, the Kaduna and the Benue Rivers. Different water types were distinguished by the concentrations of major ions. The type Ca > Na > Mg > K - HCO₃ > SO₄ > Cl was represented at all stations during at least part of the year. Chloride was found to dominate the sulphate ion in the Kaduna and Niger, while the Benue maintained a higher concentration of sulphate relative to chloride all year round. Distinct patterns of seasonal variation in the ion concentrations were observed, particularly for the samples collected at Lokoja. Low ion concentrations were prominent during periods of high discharge, while low flow periods coincided with high dissolved ion concentrations. The contribution of rainwater to the total dissolved solids in the river waters was assessed indirectly using rainwater chemistry data from the Gulf of Guinea. The estimated rainwater contribution to the Lower Niger amounts to 5.15 mg 1^?1. Geochemical weathering calculations involving reactions of the four major minerals of granitic rocks - anorthite, biotite, albite, and K-feldspar - with carbon dioxide and water, can account for the average water composition of the Lower Niger. The proportion of the ionic components was also related to the occurrence of the respective element in the minerals.