Non‐linear prestack seismic inversion with global optimization using an edge‐preserving smoothing filter

Estimating elastic parameters from prestack seismic data remains a subject of interest for the exploration and development of hydrocarbon reservoirs. In geophysical inverse problems, data and models are in general non‐linearly related. Linearized inversion methods often have the disadvantage of strong dependence on the initial model. When the initial model is far from the global minimum, inversion iteration is likely to converge to the local minimum. This problem can be avoided by using global optimization methods. In this paper, we implemented and tested a prestack seismic inversion scheme based on a quantum‐behaved particle swarm optimization (QPSO) algorithm aided by an edge‐preserving smoothing ( EPS) operator. We applied the algorithm to estimate elastic parameters from prestack seismic data. Its performance on both synthetic data and real seismic data indicates that QPSO optimization with the EPS operator yields an accurate solution.     

Near‐optimal piecewise linear fits of static pushover capacity curves for equivalent SDOF analysis

The piecewise linear (‘multilinear’) approximation of realistic force‐deformation capacity curves is investigated for structural systems incorporating generalized plastic, hardening, and negative stiffness behaviors. This fitting process factually links capacity and demand and lies at the core of nonlinear static assessment procedures. Despite codification, the various fitting rules used can produce highly heterogeneous results for the same capacity curve, especially for the highly‐curved backbones resulting from the gradual plasticization or the progressive failures of structural elements. To achieve an improved fit, the error introduced by the approximation is quantified by studying it at the single‐degree‐of‐freedom level, thus avoiding any issues related to multi‐degree‐of‐freedom versus single‐degree‐of‐freedom realizations. Incremental dynamic analysis is employed to enable a direct comparison of the actual backbones versus their candidate piecewise linear approximations in terms of the spectral acceleration capacity for a continuum of limit‐states. In all cases, current code‐based procedures are found to be highly biased wherever widespread significant stiffness changes occur, generally leading to very conservative estimates of performance. The practical rules determined allow, instead, the definition of standardized low‐bias bilinear, trilinear, or quadrilinear approximations, regardless of the details of the capacity curve shape. Copyright © 2012 John Wiley & Sons, Ltd.     

Ground motion scaling methods for linear‐elastic structures: an integrated experimental and analytical investigation

The task of selecting and scaling an appropriate set of ground motion records is one of the most important challenges facing practitioners in conducting dynamic response history analyses for seismic design and risk assessment. This paper describes an integrated experimental and analytical evaluation of selected ground motion scaling methods for linear‐elastic building frame structures. The experimental study is based on the shake table testing of small‐scale frame models with four different fundamental periods under ground motion sets that have been scaled using different methods. The test results are then analytically extended to a wider range of structural properties to assess the effectiveness of the scaling methods in reducing the dispersion and increasing the accuracy in the seismic displacement demands of linear‐elastic structures, also considering biased selection of ground motion subsets. For scaling methods that are based on a design estimate of the fundamental period of the structure, effects of possible errors in the estimated period are investigated. The results show that a significant reduction in the effectiveness of these scaling methods can occur if the fundamental period is not estimated with reasonable certainty. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural pounding between adjacent buildings subjected to strong ground motions. Part II: The effect of multiple earthquakes

The effect of collision between adjacent reinforced concrete building frames under multiple earthquakes is investigated in this paper. The four planar frames and the nine different pairs of adjacent reinforced concrete structures of the first companion paper are also examined here, under five real seismic sequences. Such a sequence of earthquakes results in a significant damage accumulation in a structure because any rehabilitation action between any two successive seismic motions cannot be practically materialised because of lack of time. Various parameters are investigated, such as the maximum horizontal displacement of top floor, ductility of columns, permanent displacements and so on. Furthermore, four different separation gaps between the building frames are considered to determine their influence on the behaviour of these frames. It is concluded that in most of the cases, the seismic sequences appear to be detrimental in comparison with the single seismic events. Copyright © 2013 John Wiley & Sons, Ltd.     

利用时间分裂的错格伪谱法模拟地震波在基于改进BISQ模型的双相介质中的传播

改进的BISQ(Biot-Squirt)模型中各参数具有明确的物理意义和可实现性,在不引入特征喷流长度的情况下可将Biot流动和喷射流动两种力学机制有机地结合起来;而高精度的地震波场数值模拟技术是研究双相介质地震波传播规律的重要手段。本文从本构方程、动力学方程和动力学达西定律出发,推导了基于改进BISQ模型的双相各向同性介质的一阶速度--应力方程组;采用时间分裂错格伪谱法求该方程组的数值解,模拟半空间及层状双相介质中的地震波场。数值模拟结果表明:①与传统方法相比,时间分裂错格伪谱法波场数值模拟的精度更高,压制网格频散效果更好;②在非黏滞相界情况下,慢纵波呈传播性,而在黏滞相界情况下,慢纵波呈扩散性,以静态模式出现在震源位置;③双相介质分界面处,各类波型复杂的反射透射规律可由数值模拟结果清晰展现。     

黑土区土壤有机质和全氮含量遥感反演研究

以东北典型黑土区耕地为研究区,以Sentinel-2A（全球环境与安全监测计划的第二颗卫星,于2015年6月23日发射）影像作为数据源,构建光谱指数,分别采用多元逐步线性回归（Multiple Stepwise Linear Regression, MSLR）和随机森林（Random Forest, RF）算法建立土壤有机质（SOM）和土壤全氮（STN）预测模型,并采用十折交叉验证方法评估模型的性能。研究对比分析了不同气候、土壤类型和地形下土壤有机质和全氮的空间分布差异。研究表明：① 海伦示范区的SOM和STN含量最高,其年均温最低,高程最高,年降水量多,SOM含量升高,其年均温最低,年降水量多,STN含量升高;② 与基于多元逐步线性回归算法建立的SOM和STN预测模型相比,随机森林算法建立的SOM和STN预测模型,有着更高的精度和稳定性;③ 运用RF算法建立的SOM反演模型的R²为0.96,均方根误差为5.49 g/kg,STN反演模型的R²为0.95,均方根误差为0.27 g/kg; ④ 不同示范区统一建立SOM和STN预测模型,有助于提高预测精度,实现跨区域建模与制图。     

中国城市流动人口社会融合的空间格局与影响机制

城市流动人口的社会融合是新型城镇化建设的重点任务。针对现有研究在社会融合的空间特征及流入地作用方面的研究不足,本文基于2017年全国流动人口动态监测调查数据,引入空间分析和分层线性模型,揭示了中国地级以上城市流动人口社会融合的空间格局与影响机制。研究发现：① 中国城市流动人口的总体社会融合指数为0.43,存在行为融合（0.71）>心理融合（0.61）>经济融合（0.33）的维度特征。② 流动人口的社会融合存在空间自相关性和集聚性,高水平社会融合区主要分布在东北地区、山东半岛和川渝地区,低水平社会融合区主要分布在东南沿海、关中平原和华北平原地区。在这些地区中,总体上存在人口50万以下的小城市的流动人口社会融合水平高于大城市的基本特征。③ 流入地因素和个体因素共同影响和形塑了流动人口社会融合的水平和空间格局,且流入地的人口规模、住房支出（房价水平）和公共服务等因素对个体因素的影响具有调节作用,包含正向极化、负向极化、正向均化、负向均化等4种调节机制。本文呼吁从流入地—个体因素关联的人地关系视角开展流动人口社会融合研究,重视流入地因素对个体因素的影响,为基于流入地的政策调控来推进新型城镇化建设提供科学依据。     

双线偏振雷达差分反射率因子系统误差订正

差分反射率因子ZDR易受雷达系统自身的影响而产生明显偏差,这种偏差是不随空间积累而改变的.为了保证雷达资料及其产品的质量,根据中国气象科学研究院灾害天气国家重点实验室车载C波段双线偏振多普勒雷达(C-band Polarimetric Doppler Radar on Wheel,CPDRW)的外场试验,对观测的ZDR进行了分析,并以垂直扫描数据的订正结果为参考,重点讨论了以体扫模式最高仰角下的小雨和干雪这两种自然目标物为订正对象得到的订正结果.结果表明,高仰角体扫资料的这两种自然目标物都能较好地订正ZDR的系统误差.但相较于小雨,干雪的订正效果更加稳定,是进行ZDR系统误差订正的最优气象目标物,而利用高仰角体扫资料的干雪粒子进行ZDR系统误差订正也就成为垂直扫描订正法的最佳替代方法.     

非量测数码相机内方位元素测量研究

阐述了非量测数码相机内方位元素的概念、测定的原理和方法,以及在成像过程中产生误差的来源。使用共线条件方程的基本原理,选取合适的模型,利用澳大利亚墨尔本大学的Australis软件解算得到内方位元素,并分析结果的可靠性。     

Three-image matching. For 3-D linear object tracking

This paper will discuss strategies for trinocular image rectification and matching for linear object tracking. It is well known that a pair of stereo images generates two epipolar images. Three overlapped images can yield six epipolar images in situations where any two are required to be rectified for the purpose of image matching. In this case, the search for feature correspondences is computationally intensive and matching complexity increases. A special epipolar image rectification for three stereo images, which simplifies the image matching process, is therefore proposed. This method generates only three rectified images, with the result that the search for matching features becomes more straightforward. With the three rectified images, a particular line-segment-based correspondence strategy is suggested. The primary characteristics of the feature correspondence strategy include application of specific epipolar geometric constraints and reference to three-ray triangulation residuals in object space.