Surface gravitational field and topography changes induced by the Earth’s fluid core motions

Using a Love number formalism, the elastic deformations of the mantle and the mass redistribution gravitational potential within the Earth induced by the fluid pressure acting at the core–mantle boundary (CMB) are computed. This pressure field changes at a decadal time scale and may be estimated from observations of the surface magnetic field and its secular variation. First, using a spherical harmonic expansion, the poloidal and toroidal part of the fluid velocity field at the CMB for the last 40 years is computed, under the hypothesis of tangential geostrophy. Then the associated geostrophic pressure, whose order of magnitude is about 1000 Pa, is computed. The surface topography induced by this pressure field is computed using Love numbers, and is a few millimetres. The mass redistribution gravitational potential induced by these deformations and, in particular, the zonal components of the related surface gravitational potential perturbation (J₂, J₃ and J₄ coefficients), are calculated. Overall perturbations for the J₂ coefficient of about 10^–10, for J₃ of about 10^–11 and for J₄ are found of about 0.3×10^–11. Finally, these theoretical results are compared with recent observations of the decadal variation of J₂ from satellite laser ranging. Results concerning J₂ can be described as follows: first, they are one order of magnitude too small to explain the observed decadal variation of J₂ and, second, they show a significant linear trend over the last 40 years, whose rate of decrease amounts to 7% of the observed value.     

Détermination indirecte des limites d'Atterberg par gravimétrie dynamique

This study presents a new method for Atterberg limits measurements using dynamic drying. Indeed, for some polluted clays, or clay mixtures, classical methods cannot be used. The principle of liquid $(W_{\mathrm{L}})$ and plasticity $(W_{\mathrm{P}})$ limits determination by this method is presented. Experimental values for classical clays are close to those obtained with Casagrande's methods, allowing for larger physical mud characterisation. To cite this article: C. Proust et al., C. R. Geoscience 336 (2004).     

基于模糊故障树的GIS产品的可靠性分析

本文首次把模糊故障树方法引入到GIS产品的可靠性分析,并就模糊故障树的基本理论作了简单的介绍,阐述了模糊故障树的建造和基于三角模糊数和梯形模糊数运算规则,结合GIS产品的特性论述了模糊故障树用于GIS产品可靠性分析的步骤,然后用实例进行了分析,最后就全文进行总结并指出了需要解决的问题。     

A Case Study of Cloud-to-Ground Lightning Activities in Hailstorms under Cold Eddy Synoptic Situation

There were three hailstorms in Shandong Province,caused by a same northeast cold eddy situation on 1 June 2002.Cloud-to-ground (CG) flashes occurring in the weather event were observed by Shandong Lightning Detection Network (SLDN),which consists of 10 sensors covering all over Shandong Province.The temporal and spatial distributions of CG lightning are investigated for the three hailstorms by using the data from SLDN,Doppler radar and satellite.The results show that different thunderstorms present different lightning features even if under the same synoptic situation.The percentage of positive CG lightning is very high during the period of hail falling.CG flashes mainly occurred in the region with a cloud top brightness temperature lower than -50°C.Negative CG flashes usually clustered in the lower temperature region and tended to occur in the region with maximum temperature gradient,while the positive ones usually spread discretely.Negative CG flashes usually occurred in intense echo regions with reflectivity greater than 50 dBz,while the positive CG flashes often occurred in weak and stable echo regions (10-30 dBz) or cloud anvils,although they can be observed in strong convective regions sometimes.Almost all hail falling took place in the stage with active positive flashes,and the peak positive flash rate is a little prior to the hail events.The thunderstorm could lead to disastrous weather when positive CG lightning activities occur in cluster.Severe thunderstorms sometimes present a low flash rate at its vigorous stage,which is probably caused by the"mechanism of chargeregion lift"through investigating the reflectivity evolution.Combined with the total lightning (intracloud and CG) data obtained by LIS onboard TRMM,the phenomenon of high ratio of intracloud flash to CG flash in severe hailstorm has been discussed.The competition of the same charge sources between different lightning types can also be helpful for explaining the cause of low CG lightning activities in severe storms.     

GridGIS若干关键技术研究

分析了当前地理信息系统运用和功能现状,提出了网格地理信息系统的4点技术特征,并在此基础上提出了一种以服务为中心的体系结构.针对面向对象空间数据模型无法描述许多广泛存在却无法用属性、方法和事件来描述的地理逻辑,以及空间数据语意不一致带来的数据集成和综合应用问题,提出了一种基于规则的空间数据组织模式.针对网格环境下空间信息的深度共享问题,提出了一种结合Multi-Agents和Web Services这两种分布式计算技术的空间信息服务模式.     

利用物理方法确定外方位元素的卫星立体摄影测量的精度分析

本文在分析用物理方法确定外方位元素的情况下卫星立体摄影测量的精度影响因素,推导了卫星立体摄影测量的理论精度计算公式,并以SPOT5 HRS立体像对为例,计算了SPOT5 HRS立体测量的理论精度,进行了利用少量地面控制点的立体测量试验。结果证明卫星立体摄影测量的理论精度估算公式是正确的,同时SPOT5 HRS立体测量精度能够满足1∶50000测图的要求。     

Mental maps and travel behaviour: meanings and models

In this paper, the “mental map” concept is positioned with regard to individual travel behaviour to start with. Based on Ogden and Richards’ triangle of meaning (The meaning of meaning: a study of the influence of language upon thought and of the science of symbolism. International library of psychology, philosophy and scientific method. Routledge and Kegan Paul, London, 1966) distinct thoughts, referents and symbols originating from different scientific disciplines are identified and explained in order to clear up the notion’s fuzziness. Next, the use of this concept in two major areas of research relevant to travel demand modelling is indicated and discussed in detail: spatial cognition and decision-making. The relevance of these constructs to understand and model individual travel behaviour is explained and current research efforts to implement these concepts in travel demand models are addressed. Furthermore, these mental map notions are specified in two types of computational models, i.e. a Bayesian Inference Network (BIN) and a Fuzzy Cognitive Map (FCM). Both models are explained, and a numerical and a real-life example are provided. Both approaches yield a detailed quantitative representation of the mental map of decision-making problems in travel behaviour.     

一种有效的航拍图像中直线提取算法

首先对航拍图像进行小尺度高斯滤波;然后进行边缘检测,得到边缘检测幅度图像;再在边缘检测幅度图像中进行启发式搜索连接,提取出符合直线模型的直线搜索轨迹;最后根据直线搜索轨迹的判别获取直线。实验结果表明,该算法可以在航拍图像中提取出真实的直线,是一种有效的直线提取算法。     

城市地质灾害应急管理平台的设计与研究

我国地质灾害多发,严重威胁到山地城市安全.城市地质灾害应急管理的首要环节是应急部门对信息的及时沟通和决策部门对信息的高效管理.因此,设计具有完善的数据共享模式,并具备良好服务架构的信息平台是科学应急管理的必要手段.本文研究了城市地质灾害应急管理平台设计中的关键技术,提出了基于地理网络和元数据管理的数据共享模式;建立了基于SOA的平台架构,并描述了分布式环境下的平台配置结构.通过引入先进的软件技术和GIS技术,可以为城市地质灾害救援指挥提供必要的信息和技术支撑,最终实现减轻城市突发性地质灾害损失的目的.     

GPS/BD静态相对定位解算研究与实现

BD系统的投入使用改变了传统的单星座静态相对定位解算方法,使GPS/BD双星座相对定位解算成为可能,本文论述了GPS/BD静态相对定位解算的数学模型,对载波相位频率不同的双星座整周模糊度固定方法进行了阐述;利用中海达新版后处理软件HGO软件来实现相关算法,并用通过实测数据进行了多项试验,证明了GPS/BD静态相对定位解算的正确性和可靠性。