CT图像三维重建

本文对由二维断面序列图像重建人体器官三维结构实现进行了研究。通过ＣＴ磁带媒介实现断面图像的获取，保障了输入数据的精度；基于形状的目标内插产生二值体数据，避免了线性灰度插值造成的物体表面边界模糊，并减少了分割的工作量；采用一种改进的扫描线编码对二值体数据进行压缩，在ＰＣ机有限的资源下实现了三维物体的快速旋转和多种方式显示。     

《CT理论与应用研究》约稿函

<正>尊敬的先生/女士:CT(Computerized Tomography-计算机断层成像,是一种在不破坏物体结构的前提下,根据物体周边所获取的某种物理量(如地震波、X射线等)的投影数据,运用一定的数学方法,通过计算机处理,重建物体特定层面上的二维图像,以及依据一系列上述二维图像构成三维图像的技术。随着CT技术和各专业学科的发展,CT在物质探测方面所具有巨大的优势,在医学、工业、地球物理、工程、农业、安全检测等领域得到了广泛的应用。     

《CT理论与应用研究》约稿函

正尊敬的先生/女士:CT(Computerized Tomography)——计算机断层成像,是一种在不破坏物体结构的前提下,根据物体周边所获取的某种物理量(如地震波、X射线等)的投影数据,运用一定的数学方法,通过计算机处理,重建物体特定层面上的二维图像,以及依据一系列上述二维图像构成三维图像的技术。     

《CT理论与应用研究》约稿函

正尊敬的先生/女士:CT(Computerized Tomography)——计算机断层成像,是一种在不破坏物体结构的前提下,根据物体周边所获取的某种物理量(如地震波、X射线等)的投影数据,运用一定的数学方法,通过计算机处理,重建物体特定层面上的二维图像,以及依据一系列上述二维图像构成三维图像的技术。     

医学图像三维表面模型重建

三维表面模型重建是医学图像处理的重要内容,是将CT和MRI等医疗影像设备获得的二维图像重建成三维立体表面显示图像的过程.本文重点研究了其重建算法的具体实现:(1)在建模上采用了基于体素的三维物体体积重建;(2)在显示上提出了基于Ray-Casting的三维物体二维直接显示技术.所以,和传统采用三角面拟合的方法相比,具有图像重建过程无需生成中间数据、无需进行3D物体的边界检测等优点,同时该算法并行性好,易于采用硬件方法实现加速.因此,本研究为医学图像三维表面模型重建应用软件的开发打下了理论基础.     

一种工业CT图像的分割算法

由于工业CT图像结构复杂,存在各种伪影,并且灰度分布呈现区域性质等特点,难以准确找出分割阈值,为此提出了一种适用于工业CT图像的分割算法。首先利用最大类间方差法和图像处理方法处理了外层伪影,然后利用聚类迭代的方法处理中心空气,得到感兴趣的区域。实验结果表明,此算法能够对具有先验知识的工业断层图像准确地提取感兴趣的区域。     

径向基函数方法在南泥湾油田勘探中的应用

为明确利用奇特开发井网数据拟合地质曲面拟合的合理性和可靠性，选用多二次曲面函数进行插值计算.该方法具有数学算法简单、计算灵活、易于实现及结果比较准确等诸多优点，适合用于散乱数据的插值.通过实例的分析验证，证明了该方法在建立散乱数据点地质曲面时具有良好的逼近效果，可以反映比较真实的地质现象.     

曲率属性计算方法研究及效果分析

曲率属性近年来在地震资料解释上得到了迅速的发展和应用,而曲率属性的计算通常使用3×3网格单元对二次曲面进行拟合,由Roberts推导并给出了具体的计算公式.本文以Roberts推导的思路为基础,应用中心差分方法计算空间导数,引入微分算子的形式来表示,并且在3×3网格拟合的基础上,推导了5×5网格单元对二次曲面进行拟合得到的各种曲率属性的计算公式,并对3×3网格、5×5网格求取曲率的结果进行了对比分析.结果表明,5×5网格拟合结果在断层和构造特征的识别方面有着良好的实际结果.     

煤岩CT图像二值化阀值选取及三维重构技术研究

运用工业cT实验系统（简称为DT-3）对煤样完成单轴加载实验,并对煤样进行一系列断层扫描,获取到不同截面处的破坏cT图像。基于图像分割技术,对图像的灰度级别设定不同的二值化阀值,得出不同阀值下的孔隙面积变化曲线图;并提出以拐点处对应的阀值作为裂隙图像二值化阀值时效果最佳。由上述研究结果结合灰度线性加权平均插值方法,编程实现了煤岩CT图像的三维重构,为后续研究煤岩裂隙三维表征提供了科学依据。     

局部断层精确计算定理的证明

本文给出了局部断层图像重建精确计算定理的简单证明。局部断层图像重建是一类仅需较少的扫面数据的断层成像技术,可以有效降低扫面物体的辐射剂量,提高图像重建速度。文献[6]针对局部断层成像的概念提出了一种扇形束的一般扫描轨道的局部断层的精确图像重建方法。本文为文献[6]的定理提供了一个简捷的证明。     

Numerical modelling of stratified flow: a spectral approach

A numerical formulation is developed to solve the three-dimensional hydrodynamic equations which describe flow in a stratified sea.Arbitrary continuous physically realistic variations of density and eddy viscosity can be included in the model, which is sufficiently flexible to be applicable to sea areas of any horizontal extent and depth. A continuous current profile from sea surface to sea bed, is computed with the model. A method for expanding computed current profiles in terms of vertical modes is proposed and the contribution of these modes to the current profiles is considered.The time variation of the wind-induced circulation of a stratified lake in response to a suddenly imposed and maintained wind stress is examined. Calculations show that the wind-driven surface current is modulated by the internal seiche motion of the lake.     

基于微焦点CT与数据约束模型的古代家猪牙齿显微结构研究

本文对一例考古发掘出土的古代家猪下颌骨及牙齿进行了微焦点CT成像,通过加置滤波片有效减弱了线束硬化对CT图像的影响。基于数据约束模型（DCM）对样品三维结构进行了定量计算,获取了包含小于CT图像体元尺寸在内的样品跨尺度结构信息。对样品中孔隙及高吸收组分的联通特性进行了跨尺度计算,得到这两种组分的三维团簇分布。与常见的图像阈值分割法相比,DCM模型有效减弱了部分体积效应对图像分析的影响。本文研究结果为考古样品的内部形态测量、结构分析提供了数据基础,为考古样品的数字建模存档提供一种新的方法。      

多尺度分割和深度学习相结合的倾斜摄影三维影像建筑物震害信息提取

采用多尺度分割和深度学习相结合的方法对震后倾斜摄影三维影像建筑物震害信息进行提取,获取建筑物的屋顶和墙体多种破坏信息。以2017年九寨沟M_S7.0地震后倾斜摄影三维影像为例,依据三维影像建筑物顶面和墙体等进行样本的多尺度分割,样本分为完好建筑物面、破坏建筑物面、其它地物和背景等三类,选取211个100×100像素的样本集对卷积神经网络模型进行训练,采用训练后的模型提取灾区千古情风景区和漳扎镇小学的建筑物震害信息,并将提取结果与目视解译结果进行精度对比,结果显示:破坏建筑物面提取精度分别为65.5%和71.1%,总体分类精度分别为82.1%和84.1%,卡帕（Kappa）系数分别为68.7%和64.9%,表明该方法在倾斜摄影三维影像建筑物震害提取方面具有一定的优势。      

大气-水耦合模式下三维太湖湖流场研究

利用太湖区域的大气边界层三维数值模式和三维水动力学数值模式,采用气-水耦合方法,对太湖的风生流特征进行了深入研究。结果表明,太湖区域大气边界层风场具有明显的时空变化特征,与均匀定常风作用下的太湖流场相比,大气-水耦合模式下太湖流场变化较大,形成稳定湖流场所需的时间也较长。三维模式计算出的流速值明显比二维模式大(表层约大一倍,整层平均约大50％),且与实际观测值符合较好。故即使对于像太湖这样的浅水湖泊,三维水动力学模式的应用仍然是很必要的。模拟结果中还发现湖流的上下流矢有时出现非常大的切变,甚至达到了180°。由于浅水湖中仍存在两个边界层(水-气和水-土),故浅水湖中存在流矢的巨大切变是可能的。     

Connectivity constrained segmentation of geologic features

Segmentation of geologic features plays a significant role in seismic interpretation. Based on the segmentation results, interpreters can readily recognize the shape and distribution of geologic features in three-dimensional space and conduct further quantitative analysis. Usually, there are mainly two steps for the segmentation of geologic features: the first step is to extract seismic attributes that can highlight the occurrence of geologic features, and the second step is to apply the segmentation algorithm on the seismic attribute volumes. However, the occurrence of geologic features is not always corresponding to the anomaly value on the seismic attribute volumes and vice versa because of several factors, such as noise in the seismic data, the limited resolution of seismic images and the limited effectiveness of the seismic attribute. Therefore, the segmentation results, which are generated solely based on seismic attributes, are not sufficient to give an accurate depiction of geologic features. Aiming at this problem, we introduce the connectivity constraint into the process of segmentation based the assumption that for one single geologic feature all of its components should be connected to each other. Benefiting from this global constraint, the segmentation results can precisely exclude the interference by false negatives on seismic attribute volumes. However, directly introducing the connectivity constraint into segmentation would face the risk that the segmentation results would deteriorate significantly because of false positives with relatively large area when the connectivity constraints are enforced. Therefore, based on the seismic attribute that highlights the boundary of geologic feature, we further propose a post-processing technique, called pruning, to refine the segmentation results. By taking the segmentation of the channel as an example, we demonstrate that the proposed method is able to preserve the connectivity in the process of segmentation and generate better segmentation results on the field data.     

三维可视化在CSAMT勘探中的应用

CSAMT法是一种强有力的地球物理勘探手段,具有测量迅速、探测深度大、信噪比高等优点,已被广泛应用于金属矿、油气田、地下水、以及地热田的勘探中.在CSAMT勘探资料解释方面,传统的二维电阻率断面很难清晰、直观地揭示3D(三维)地电结构的分布特征,为此应加强3D可视化应用技术的研究.本文详细的介绍了3D可视化的建模过程,将3D构造的建模分为空间曲面剖分、空间曲面拟合插值、空间曲面拓扑关系生成、3D结构网格剖分、属性建模等过程.并以一个CSAMT勘探实例,展现出3D可视化方法技术的突出优势.三维可视化可以多角度、多层面展现地下3D电性结构的分布特征,使我们更加清晰、直观地了解3D地质体的空间范围与几何形态.     

基于重力卫星数据监测地表质量变化的三维点质量模型法

利用卫星重力测量手段监测全球质量变化取得了巨大成功,本文基于牛顿万有引力定律在三维空间直角坐标系中导出利用重力卫星观测数据监测全球质量变化的三维点质量模型法,该方法可直接利用重力卫星的轨道和星间观测数据或时变重力场模型计算全球质量变化,由于利用卫星观测数据计算地表质量变化的向下延拓过程以及观测数据噪声的影响,需要采用合适的空间约束方程或正则化技术对解算结果进行约束或平滑处理.利用合成全球质量变化模型模拟一个月的GRACE双星轨道和星间距离变率数据计算全球质量变化,对三维点质量模型法进行分析验证,采用零阶Tikhonov正则化技术处理病态问题.结果表明,三维点质量模型法可有效用于重力卫星观测数据监测全球质量变化,为利用重力卫星观测数据监测全球质量变化提供一种可选的途径.     

Multilayer analytic element modeling of radial collector wells

A new multilayer approach is presented for the modeling of ground water flow to radial collector wells. The approach allows for the inclusion of all aspects of the unique boundary condition along the lateral arms of a collector well, including skin effect and internal friction losses due to flow in the arms. The hydraulic conductivity may differ between horizontal layers within the aquifer, and vertical anisotropy can be taken into account. The approach is based on the multilayer analytic element method, such that regional flow and local three-dimensional detail may be simulated simultaneously and accurately within one regional model. Horizontal flow inside a layer is computed analytically, while vertical flow is approximated with a standard finite-difference scheme. Results obtained with the proposed approach compare well to results obtained with three-dimensional analytic element solutions for flow in unconfined aquifers. The presented approach may be applied to predict the yield of a collector well in a regional setting and to compute the origin and residence time, and thus the quality, of water pumped by the collector well. As an example, the addition of three lateral arms to a collector well that already has three laterals is investigated. The new arms are added at an elevation of 2 m above the existing laterals. The yield increase of the collector well is computed as a function of the lengths of the three new arms.     

基于L1范数正则化的强震动加速度记录基线漂移识别方法

本文提出了一种基于L₁范数正则化的基线校正新方法,即以拟合速度时程误差最小为目标,以基线漂移本身尽可能小为约束条件,经过凸优化多次迭代自动求解出满足条件的基线漂移,避免了人为选取基线漂移分段次数和基线漂移起止时刻的主观干扰;随后利用该方法对多组加入了基线漂移噪声模型的强震动加速度记录进行验证。结果表明:本文方法对于识别和处理单段式、两段式和多段式的基线漂移噪声具有普适性,能敏锐地捕捉到速度时程发生漂移的趋势（斜率变化）,无需预先设定加速度基线漂移模型也可有效地识别出多种基线漂移噪声的起止位置和漂移程度;地震记录事前部分对本文方法处理结果影响较大,当记录事前部分足够长时（如20 s）,识别基线漂移噪声的准确性较高,位移时程可以较好地与原始位移匹配;而对于发生漂移的速度时程,本文方法可以不受地震事前部分长短的干扰,甚至在加速度记录出现明显丢头现象时,也能很好地实现峰值速度和整个速度时程的恢复。      

Three-dimensional semi-idealized model for tidal motion in tidal estuaries

In this paper, a three-dimensional semi-idealized model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This model aims at bridging the gap between idealized and complex models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-idealized model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed idealized models. The new model also retains the flexibility and computational efficiency of previous idealized models, essential for sensitivity analysis. As a first step, the accuracy of the semi-idealized model is investigated. To this end, an extensive comparison is made between the model results of the semi-idealized model and two other idealized models: a width-averaged model and a three-dimensional idealized model. Finally, the semi-idealized model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the model is applied to the Ems estuary. The model results agree well with observations and results from a complex numerical model.