X波段雷达图像反演风场光流方法的改进

风是一种重要的海洋环境动力学要素,海洋风场信息可以从X波段雷达海杂波图像中提取。本文从高阶次波的频散关系、贝叶斯方法和求解光流方程的全局平滑约束技术等方面对现有的X波段雷达反演风场的光流方法进行了改进,并利用实测数据对反演结果进行了验证。结果表明,改进方法反演的风向和风速较之原方法的反演结果都有了显著改善,与实测结果符合更好。此外,改进方法的反演结果能够很好地反映近岸风向和风速的整体变化趋势。     

改进约束D-TIN的等高线陡坡区域识别

针对高线图中陡坡区域特征的自动识别问题,在应用Delaunay三角网与线性插值法生成等高线图的基础上,改进了基于最大角原则生成约束Delaunay三角网的算法,对等高线图进行了三角剖分,根据等高线之间约束三角形的几何参数,计算了等高线图坡面单元坡度,识别出坡度较高区域。进一步地,给出了一种扩张算法对相连陡坡单元进行划分形成陡坡区域,计算了各个陡坡区域中心坐标、面积与平均坡度。通过对12组有256个坐标高程值的数据构建约束D-TIN并生成三维地形图对识别结果进行了评价,识别正确率达0.903,平均识别时间为33ms。实验表明,对于不同数据生成的不同等级等高线图的识别结果均有较高的效率与准确率。     

An analytic solution to the alibi query in the space–time prisms model for moving object data

Moving objects produce trajectories, which are stored in databases by means of finite samples of time-stamped locations. When speed limitations in these sample points are also known, space–time prisms (also called beads) (Pfoser and Jensen 1999 Pfoser, D. and Jensen, C.S. 1999. “Capturing the uncertainty of moving-object representations”. In Advances in spatial databases (SSD’99), Hong Kong, China, July 20–23, 1999, Vol. 1651, 111–132. Lecture notes in Computer Science.  [Google Scholar], Egenhofer 2003 Egenhofer, M. 2003. “Approximation of geopatial lifelines”. In SpadaGIS, workshop on spatial data and geographic information systsems, 4SpaDaGIS–Workshop on Spatial Data and Geographic Information Systems, Milano, Italy, March 2003. University of Genova.  [Google Scholar], Miller 2005 Miller, H. 2005. A measurement theory for time geography. Geographical Analysis, 37(1): 17–45. [Crossref], [Web of Science ®] , [Google Scholar]) can be used to model the uncertainty about an object's location in between sample points. In this setting, a query of particular interest that has been studied in the literature of geographic information systems (GIS) is the alibi query. This boolean query asks whether two moving objects could have physically met. This adds up to deciding whether the chains of space–time prisms (also called necklaces of beads) of these objects intersect. This problem can be reduced to deciding whether two space–time prisms intersect.

The alibi query can be seen as a constraint database query. In the constraint database model, spatial and spatiotemporal data are stored by boolean combinations of polynomial equalities and inequalities over the real numbers. The relational calculus augmented with polynomial constraints is the standard first-order query language for constraint databases and the alibi query can be expressed in it. The evaluation of the alibi query in the constraint database model relies on the elimination of a block of three exªistential quantifiers. Implementations of general purpose elimination algorithms, such as those provided by QEPCAD, Redlog, and Mathematica, are, for practical purposes, too slow in answering the alibi query for two specific space–time prisms. These software packages completely fail to answer the alibi query in the parametric case (i.e., when it is formulated in terms of parameters representing the sample points and speed constraints).

The main contribution of this article is an analytical solution to the parametric alibi query, which can be used to answer the alibi query on two specific space–time prisms in constant time (a matter of milliseconds in our implementation). It solves the alibi query for chains of space–time prisms in time proportional to the sum of the lengths of the chains. To back this claim up, we implemented our method in Mathematica alongside the traditional quantifier elimination method. The solutions we propose are based on the geometric argumentation and they illustrate the fact that some practical problems require creative solutions, where at least in theory, existing systems could provide a solution.     

音频大地电磁法对隐伏构造的识别与应用——以河南省郑州市老鸦陈周边为例

为探明郑州市及其周边地区隐伏构造的分布情况,在郑州北郊老鸦陈断层东侧布设了一条EW向音频大地电磁(AMT)测线,并对野外数据进行了去噪、主轴旋转、阻抗分析、静态校正等处理。用正则化反演理论方法——非线性共轭梯度法(NLCG)进行二维反演,利用与AMT测线接近平行的地震剖面分层结果对模型进行约束反演,降低了反演的多解性以及NLCG对初始模型的依赖性,最终取得了较好的电性结果。结果表明测线下方分为3层,并有一隐伏构造。结合地质、地球物理资料推断解释,此隐伏构造有可能是一条发育在晚新近系的正断层,亦或为第四系地层与新近系地层的不整合接触面。本文的研究工作为进一步探明城市隐伏构造提供了地球物理及技术手段依据。     

A Direct Inverse Model to Determine Permeability Fields from Pressure and Flow Rate Measurements

The determination of the permeability field from pressure and flow rate measurements in wells is a key problem in reservoir engineering. This paper presents a Double Constraint method for inverse modeling that is an example of direct inverse modeling. The method is used with a standard block-centered finite difference method. With an a priori grid block permeability field as input, two forward runs are made: the first is constrained with the measured pressures; the second is constrained with the measured flow rates. We calculate the pressures in the grid block centers from the first run, while from the second run we calculate the fluxes through the faces between the grid blocks. Substitution of these pressures and fluxes into Darcy’s law then yields the transmissibilities at the faces and hence the permeabilities in the grid blocks. In this way the “hard” data (measured pressures and flow rates) are always honored while the “soft”, geological data can be incorporated at the discretion of the geologist. Using a synthetic example, we demonstrate the method and compare the results with another method: Ensemble Kalman Filtering. The two methods agree within the scope of their applicability. The Double Constraint method focuses initially on determining spatial distributions of the permeability field for single-phase, steady state flow. For history matching an extension is required to non-steady state, two-phase flow conditions, which is already possible with EnKF. We are currently investigating the possibility of combining the two methods, whereby the strengths of the two methods could be fully exploited.     

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特征提取和特征匹配改进方法的研究

在分析了几种常用的特征提取和图像匹配算法的基础上,针对影像上纹理特征稀少、影像对比度不明显的问题,提出先用高斯差分方法突出图像特征,再用Harris特征点提取算法进行特征提取的方法;针对如同建筑物等相似特征较多的情况,利用双向特征匹配、经过斜率约束得到的结果计算视差,再进行图像匹配,可以将特征匹配限制在相关的小范围内,由此得到的同名点对比较可靠,并且提高了效率。实验证明该算法适合特征稀少不明显区域、建筑物等相似特征较多的图像匹配,具有一定的实际意义。     

Geodatabase模型的数据质量约束机制研究

为了控制和加强原始地理数据的应用质量,Geodatabase数据模型在引入地理要素的关系、行为和规则的同时定义了一系列约束机制对数据的属性域、关系以及拓扑几何关系方面进行约束,无需编码便可减少原始数据在输入、变更等过程中的错误。文章研究Geodatabase模型中的数据质量约束机制,并以道路网数据库的建立为例说明其在数据质量约束中的应用。     

测绘仪器设备状态监测数据实时压缩方法

提出基于约束点的测绘仪器设备状态监测数据实时压缩方法,通过特征序列重组,构建测绘仪器设备状态监测数据的共轭模型,输出监测数据的相关序列,结合自定义数据处理逻辑结构设计方法,检索监测数据库,采用全局稳态性的传感节点部署方法,采集测绘仪器设备状态监测数据。根据采集结果,利用最大扩充相容分布,结合内源融合控制,对监测数据融合聚类处理。在此基础上,采用二乘规划和线性特征拟合方法提取数据特征约束点,根据提取结果,构建数据实时压缩模型,实现了测绘仪器设备状态监测数据的实时压缩。仿真结果表明,采用该方法进行测绘仪器设备状态监测数据压缩率较高,提高了数据的存储空间,且具有较高的兼容度。     

高程约束法在GPS导航中的应用

介绍一种采用高程信息辅助GPS接收机定位的方法,提高了在信号受遮挡时GPS系统定位精度与导航成功率,并通过试验数据进行了验证。