点状地名信息的加权泰森多边形检索法

鉴于地名库中多数地名仅以中心点坐标形式记录其空间位置信息,缺乏其空间范围的具体描述,造成地名检索中的片面性和局限性,本文在深入分析地名及其空间属性、空间关系的基础上,考虑同类型地名的不同性质在检索中的重要作用,利用泰森多边形在地名边界近似中的优势,提出了针对点状地名信息的加权泰森多边形检索法,依据同类型地名的面积属性作为权重指标构建泰森多边形,以近似表达地名的空间范围,进而描述地名间的各类空间关系;并从拓扑关系、方位关系与距离关系3个方面给出了具体公式以计算地名间的空间相似性;最后以行政区划边界近似与检索为例验证该方法。试验结果表明,该方法可较好地近似表达地名空间范围及空间关系,增强了检索词与地理信息资源在空间位置上的相似性度量,检索结果优于传统方法。     

A New Parameterization of Canopy Radiative Transfer for Land Surface Radiation Models

A new parameterization of canopy asymmetry factor on phase function,which is dependent on the leaf normal distribution and leaf reflection/transmission,is derived. This new parameterization is much more accurate than the existing scheme. In addition,the new solutions for both the diffuse and direct radiation can be obtained using the Eddington approximation. It is found that the direct radiation can be described as a function of the diffuse radiation. This new approach offers a substantial improvement in accuracy,as compared with the hemispheric constant method,for both isotropic and anisotropic cases. Given the analytical nature of the solution and its high accuracy,we recommend the new parameterization for application in land surface radiation modeling.     

基于拟线性Born近似的叠前深度偏移方法

在频率波数域和频率空间域实现了一种基于拟线性Born近似的叠前深度偏移方法，并在2-D空间进行了Marmousi模型炮集数据的处理.通过与Split-StepFourier、Phase-Screen和稳定的Born近似叠前深度偏移等方法比较，认为基于拟线性Born近似的叠前深度偏移方法不仅在效果上要优于前三者，而且还能更好地处理速度横向变化.在散射波场计算中，使用了一个更稳定的散射波场计算公式，扩大了拟线性Born近似的应用范围，使基于拟线性Born近似的叠前深度偏移方法能够适应更强的横向速度变化.     

太平洋大尺度环流数值模拟 I:数学模式及其性能

本工作基于曾庆存的海洋环流模式设计思想和大气物理研究所海洋环流模式(IAPOGCM)基本动力框架,设计并实现了四层太平洋环流模式;同时引进稳定有效的时间积分方案和海表热通量参数化方法,对太平洋大尺度环流进行了较为系统的数值模拟. 本文首先导出消除“刚盖”近似、扣除海洋标准层结、保持总有效能量守恒的OGCM基本方程组;给出空间差分格式和时间积分方案,引入海表热通量计算方法;然后,在太平洋区域对所设计的四层OGCM的一些模式性能进行了分析、表明,时间积分方案采用基于“灵活性系数”技术的加速收敛方法和适应过程中流场正压斜压进一步分解算法,同时采取一些技术处理,可确保模式稳定而有效地进行长时间数值积分、有效能量分析表明,与海面起伏相联系的有效表面位能是总有效能量的重要组成部分,它与动能同量级甚至更大些,因此在OGCM中须考虑有效表面位能与其它能量间的转换机制,这在物理上更加合理,而采用“刚盖”近似则是不合理的;同时,扣除海洋标准层结,缩小了位能与动能之间的量级差别,有利于长期数值积分的稳定进行.此外,这个模式能直接计算海面起伏和分析有效能量,使得表面流场和上层海洋热储率的模拟比已有文献的结果有明显的改进.除模式设计外,本部分只给出模式的基本性能,系统的模拟结果将在第Ⅱ,Ⅲ两部分发表.     

Fresnel zone inversion for lateral heterogeneities in the earth

We propose a different kind of seismic inversion from travel-time or waveform inversion for lateral heterogeneities in the earth: Fresnel zone inversion. Amplitude and phase delay of data in several frequency ranges are inverted for model space around ray paths with a width corresponding to the considered frequency so that primary effect of finiteness of wavelength be included. For vertically heterogeneous media, Fréchet derivatives for inversion are obtained very efficiently using the paraxial ray approximation, with nearly similar amounts of computation compared to travel-time inversion. As an example, Fréchet derivatives are computed for a teleseismic observation system for a three-dimensional structure in the lithosphere beneath an array of seismic stations. Even if the used frequency is around 2 Hz, the width of Fréchet derivatives cannot be neglected, particularly near the bottom of the lithosphere. Sensitivity of model parameters to observations is, moreover, different in our approach from conventional travel-time inversion: it is zero along ray paths but large slightly away from them. Some model calculations show that travel-time inversion, particularly with models divided into very fine meshes or blocks, might give misleading results. An example of inversion for a simple Camembert model, in the event that travel-time inversion gives no reliable results, shows how this technique works with much smaller data sets and computation than waveform inversions.     

Bayes estimate of the probability of exceedance of annual floods

In this paper Lindley's Bayesian approximation procedure is used to obtain the Bayes estimate of the probability of exceedence of a flood discharge. The Bayes estimates of the probability of exceedence has been shown by S.K. Sinha to be equivalent to the estimate of the probability of exceedence from the predictive or Bayesian disribution, of a future flood discharge. The evaluation of complex ratios of multiple integrals common in a Bayesian analysis is not necessary using Lindley's procedure. The Bayes estimates are compared to those obtained by the method of maximum likelihood and the method of moments. The results show that Bayes estimates of the probability of exceedence are larger as expected, but have smaller posterior standard deviations.     

Magnetics in geoexploration

The magnetic method is the oldest and one of the most widely used geophysical techniques for exploring the earth’s subsurface. It is a relatively easy and inexpensive tool to employ, being applicable to a wide variety of subsurface exploration problems involving horizontal magnetic property variations occurring from near the base of the crust to within the uppermost meter of soil. Successful applications of the magnetic method require an in-depth understanding of its basic principles and careful field work, data reduction, and interpretation. Commonly, interpretations are limited to qualitative approaches which simply map the spatial location of anomalous subsurface conditions, but under favourable circumstances the technological status of the method will permit more quantitative interpretations involving specification of the nature of the anomalous sources. No other geophysical method provides critical input to such a wide variety of problems. However, seldom does the magnetic method provide the complete answer to an investigation problem. As a result, it is generally used in concert with other geophysical and geological data to limit its interpretational ambiguities.     

Latent spatio-temporal activity structures: a new approach to inferring intra-urban functional regions via social media check-in data

Abstract

This article introduces a novel low rank approximation (LRA)-based model to detect the functional regions with the data from about 15 million social media check-in records during a year-long period in Shanghai, China. We identified a series of latent structures, named latent spatio-temporal activity structures. While interpreting these structures, we can obtain a series of underlying associations between the spatial and temporal activity patterns. Moreover, we can not only reproduce the observed data with a lower dimensional representative, but also project spatio-temporal activity patterns in the same coordinate system. With the K-means clustering algorithm, five significant types of clusters that are directly annotated with a combination of temporal activities can be obtained, providing a clear picture of the correlation between the groups of regions and different activities at different times during a day. Besides the commercial and transportation dominant areas, we also detected two kinds of residential areas, the developed residential areas and the developing residential areas. We further interpret the spatial distribution of these clusters using urban form analytics. The results are highly consistent with the government planning in the same periods, indicating that our model is applicable to infer the functional regions from social media check-in data and can benefit a wide range of fields, such as urban planning, public services, and location-based recommender systems.     

Dynamic analysis of vessel/riser/equipment system for deep-sea mining with RBF neural network approximations

Abstract

Deep-sea mining (DSM) is an advanced technology. This article is focused on the dynamic analysis of a coupled vessel/riser/equipment system of a DSM based on radial basis function (RBF) neural network approximations while considering vessel dynamic positioning (DP) and active heave compensation (AHC). A coupled model including the production support vessel (PSV), lifting riser, and slurry pump is established containing simulated DP and AHC models. Furthermore, dynamic simulations are implemented to obtain the results of the vessel motions, thruster forces, pump motions and riser tensions. Using optimal Latin hypercube sampling, an RBF neural network approximation model is established, the input includes environmental factors and the output includes the dynamic responses of the pump motion and riser tension. Calculations are performed using RBF network approximations instead of a coupled model. The obtained results show that the PSV wave frequency (WF) motions have significant influence on the dynamic responses of the subsea system. Moreover, the current load affects the compensation effect. The RBF network approximation model can be used to reduce the required calculation time.     

Bottom friction and its effects on periodic long wave propagation

A new set of Boussinesq-type equations describing the free surface evolution and the corresponding depth-integrated horizontal velocity is derived with the bottom boundary layer effects included. Inside the boundary layer the eddy viscosity gradient model is employed to characterize Reynolds stresses and the eddy viscosity is further approximated as a linear function of the distance measured from the seafloor. Boundary-layer velocities are coupled with the irrotational velocity in the core region through boundary conditions. The leading order boundary layer effects on wave propagation appear in the depth-integrated continuity equation to account for the velocity deficit inside the boundary layer. This formulation is different from the conventional approach in which a bottom stress term is inserted in the momentum equation. An iterative scheme is developed to solve the new model equations for the free surface elevation, depth-integrated velocity, the bottom stress, the boundary layer thickness and the magnitude of the turbulent eddy viscosity. A numerical example for the evolution of periodic waves propagating in one-dimensional channel is discussed to illustrate the numerical procedure and physics involved. The differences between the conventional approach and the present formulation are discussed in terms of the bottom frictional stress and the free surface profiles.