Global surface wave inversion with model constraints‡

Practical applications of surface wave inversion demand reliable inverted shear‐wave profiles and a rigorous assessment of the uncertainty associated to the inverted parameters. As a matter of fact, the surface wave inverse problem is severely affected by solution non‐uniqueness: the degree of non‐uniqueness is closely related to the complexity of the observed dispersion pattern and to the experimental inaccuracies in dispersion measurements. Moreover, inversion pitfalls may be connected to specific problems such as inadequate model parametrization and incorrect identification of the surface wave modes. Consequently, it is essential to tune the inversion problem to the specific dataset under examination to avoid unnecessary computations and possible misinterpretations. In the heuristic inversion algorithm presented in this paper, different types of model constraints can be easily introduced to bias constructively the solution towards realistic estimates of the 1D shear‐wave profile. This approach merges the advantages of global inversion, like the extended exploration of the parameter space and a theoretically rigorous assessment of the uncertainties on the inverted parameters, with the practical approach of Lagrange multipliers, which is often used in deterministic inversion, which helps inversion to converge towards models with desired properties (e.g., ‘smooth’ or ‘minimum norm' models). In addition, two different forward kernels can be alternatively selected for direct‐problem computations: either the conventional modal inversion or, instead, the direct minimization of the secular function, which allows the interpreter to avoid mode identification. A rigorous uncertainty assessment of the model parameters is performed by posterior covariance analysis on the accepted solutions and the modal superposition associated to the inverted models is investigated by full‐waveform modelling. This way, the interpreter has several tools to address the more probable sources of inversion pitfalls within the framework of a rigorous and well‐tested global inversion algorithm. The effectiveness and the versatility of this approach, as well as the impact of the interpreter's choices on the final solution and on its posterior uncertainty, are illustrated using both synthetic and real data. In the latter case, the inverted shear velocity profiles are blind compared with borehole data.     

机载LiDAR点云数据中电力线的提取方法研究

提出了一种基于机载LiDAR点云数据的电力线提取方法。首先在进行LiDAR数据滤波的基础上,分离地面点与非地面点;然后针对非地面点采取一种基于角度的滤波方法,分离非地面点中的植被点与电力线点,对电力线点,采用二维Hough变换进一步分离各条电力线点;最后使用双曲余弦函数模型,对单条电力线进行曲线拟合。实验结果表明,该方法能够从LiDAR点云数据中较完整地提取出电力线点,电力线点提取正确率达96.2%,并能够对电力线走廊进行三维重建。     

基于不同拟合方法的圆曲线综合不确定性模型

分别利用直线、圆曲线与多项式曲线的拟合空间曲线实体,估计出拟合曲线与真实曲线之间的模型误差,建立包含模型误差与法线方向位置误差的曲线综合误差带模型。并通过算例证明了含有模型误差的综合误差带模型能更好地反应圆曲线的位置不确定性。     

Effects of entrapped residual air bubbles on tracer transport in heterogeneous soil: Magnetic resonance imaging study

Magnetic resonance imaging (MRI) was used to study the process of infiltration and solute transport in an undisturbed soil sample of coarse sandy loam. The sample was subjected to the recurrent ponded infiltration (RPI) experiment, which was carried out in order to assess the changes in the entrapped air volume and its impact on steady state flow rates and solute breakthrough. The main stages of the first and second experimental RPI runs were monitored using an MRI sequence that follows both water density and magnetic relaxation. In a steady state stage of each experimental run a nickel nitrate pulse was injected in order to visualize the solute breakthrough. Effluent from the sample was collected for chemical analysis and a breakthrough curve of the nickel was constructed. To obtain information about the soil structure and to reveal potential preferential pathways, the soil sample was scanned using computed tomography. The local nickel ion transport breakthrough was evaluated from MR images in a series of local observation points distributed along the selected preferential pathways.The preferential flow instability phenomenon with the emphasis on air bubble formation was shown by detecting a 60% decrease of the steady state infiltration rate. The detailed analyses of MRI measurements at observation points revealed air bubble formation, producing a flow rate decrease accompanied by redirection of nickel ion transport trajectories. By analyzing M0 maps it was found that the volumetric water content decrease was 2.2%.     

GROWTH, REPRODUCTION & POPULATION STRUCTURE OF THE FRESHWATER CRAB SINOPOTAMON YANG TSEKIENSE BOTT, 1967, FROM ZHEJIANG, CHINA

Monthly investigatiom were made on the population of Chinese freshwater crab, Sinopotamon yangteskiense Bott, 1967 from April, 1984 to Match, 1985. The data on 4413 specimens show that the growth was affected mainly by temperature. During the April to November growth period, the crabs' major development occured from June through October. One year was required for a fine white oocyte to develop into a mature egg. The reproduction period was June-October. Females bearing eggs were taken from June-August, and crabs with young were found from July-October. The females reproduced once a year but could for more than one year. The number of eggs carried by a female varied greatly according to the size of the crab, ranging from 30 to 100 eggs. New-bom crabs become mature after 1-2 yeats. The sex ratio was approximately 1:1 in the overall population. However, the larger crabs are predominantly male. The age distribution of S. yangtsekinese was estimated from size frequency histograms. There were more adult crabs     

大地电磁测深数据TE与TM极化模式的对比

在大地电磁测深工作中,由于实际地下介质的非均匀性,所得到实测资料的TE、TM极化模式视电阻率曲线有很大差异,给正确认识和判断实际地质结构带来困难。通过建立简单地堑、地垒及断层模型,并进行正反演,总结了这些模型条件下TE、TM极化模式的响应规律,为大地电磁测深数据的定性分析和解释提供了依据。     

JGS-1B智能测井仪应用中遇到的问题及解决方法

JGS-1B智能测井仪广泛应用于煤田、水文、金属矿、非金属矿及工程地质勘探.本文对该仪器在测井过程产生的深度误差、测井曲线出现跳点、测井曲线异常等问题提出了解决方法,具有示范意义.     

全吸力范围南阳膨胀土的土-水特征曲线

膨胀土的失水收缩、吸水膨胀过程分别对应着土-水特征曲线的脱湿和吸湿阶段。土-水特征曲线对于研究非饱和土的水力与力学特性有着重要作用。用压力板法（吸力范围0～1.5 MPa）、滤纸法（吸力范围0～40 MPa）和蒸汽平衡法（吸力范围3～368 MPa）,分别对南阳膨胀土进行了土-水特性试验,得到全吸力范围内的土-水特征曲线。试验结果表明：初始孔隙比大致相同土样的土-水特征曲线,在低吸力范围内脱湿曲线与吸湿曲线具有明显的滞回现象。当吸力大于300 MPa时,土-水特征曲线的滞回效应基本消失,即脱湿曲线与吸湿曲线基本重合。滤纸法所测出的土-水特性落在主脱湿和主吸湿曲线的滞回圈内。当吸力等于367.54 MPa时,含水率仅为0.325%,几乎近于0。孔隙比随着吸力的变化规律中,不仅受到吸力大小的影响,还受到吸力历史和吸力路径影响;孔隙比与吸力关系中,相同吸力时吸湿路径的孔隙比要比脱湿路径的大;在吸力低范围,吸湿路径与脱湿路径的孔隙比相近。孔隙比与饱和度关系因吸力路径的不同也存在着明显的滞回效应,接近饱和时趋近一致。变吸力情况条件下,饱和度随着孔隙比的增加而增加,蒸汽平衡法得出的孔隙比与饱和度的关系具有明显的线性关系,而压力板法做出来的低吸力范围内的线性关系不明显。     

国产矿井瞬变电磁仪的性能试验研究——与进口Terratem仪器对比

为评价国产本安型矿井瞬变电磁仪YCS40(A)的稳定性及对异常体的分辨能力,特将其同井下使用较频繁的进口仪器TERRATEM做了试验对比.试验中,进行了二款仪器使用各自的常规装置展开单点背景值实验对比、对异常体的分辨能力实验对比和抗干扰能力等模拟实验对比.并在同一感应电动势-衰减时间(V-T)的坐标下考察二者的关断时间、感应电动势的幅值、光滑程度及衰减速率和尾期信号的抗干扰度等衡量仪器性能的硬性指标.最后通过井下实际工程实例剖面测量对比,表明国产YCS40(A)矿井瞬变电磁仪具有稳定性较好、抗干扰能力强、对异常体具有较强的分辨能力等优点,同时也感到该仪器探测窗口较少、感应时间短,当井下异常体埋深超过120 m时其分辨力的不足.