Estimation of elevation-dependent satellite antenna phase center variations of GPS satellites

A method for the estimation of the phase center variations of GPS satellite antennas using global GPS data is presented. First estimations have shown an encouraging repeatability from day to day and between satellites of the same block. Thus, two different satellite antenna patterns for Block II/IIA and for Block IIR with a range of about 4 cm and an accuracy of less than 1 mm could be found. The present approach allows the creation of a consistent set of receiver and satellite antenna patterns and phase center offsets. Thereby, it is possible to switch from relative to absolute phase center variations without a scale problem in global networks. This changeover has an influence on troposphere parameters, reduces systematic effects due to uncorrect antenna modeling and should diminish the elevation dependence of GPS results. AcknowledgmentsThe authors thank Prof. G. Seeber (University of Hannover) and Dr. G. Wübbena (Geo++ GmbH) and their groups for their kindness in making available the absolute field calibration results derived from robot measurements.     

Interactive generalization on large-scale topographical map supported by a database platform

This paper makes a study on the interactive digital generalization, where map generalization can be divided into intellective reasoning procedure and operational procedure, which are done by human and computer, respectively. And an interactive map generalization environment for large scale topographic map is then designed and realized. This research focuses on: ① the significance of researching an interactive map generalization environment,② the features of large scale topographic map and interactive map generalization, ③ the construction of map generalization-oriented database platform.     

Objective Frontal Analysis Techniques Applied to Extreme/Non-Extreme Precipitation Events

A simple method of the objective frontal analysis (OFA) based on a thermal definition of atmospheric fronts is proposed for the area of Central Europe with the aid of gridded numerical weather prediction model (NWP model) outputs. The OFA includes both mathematical and graphical techniques that enable a computer to draw fronts entirely automatically in atmospheric cross-sections by means of one locating equation and four masking criteria. The OFA also enables to analyse the frontal wave position and the type, activity, and future development of fronts.The OFA is applied to two synoptically analogous cold-frontal situations, which occurred over the Czech Republic in summer season and were characterised by quite different precipitation amounts. The outputs (12h, 18h, and 24h forecasts) of the NWP model Europa Modell/Deutschland Modell are used in computations. The equivalent potential temperature is considered as an input thermal parameter of the OFA. The impact of applying and changing the OFA masking criteria is various and among others also depends on synoptic situation. The comparison between the objective and subjective analysed fronts subserves to evaluate the values of masking threshold constants. Some obtained results of the analysis of the extreme precipitation situation support the possibility of enhanced precipitation amounts. The analysis of the second non-extreme precipitation situation revealed a few different features that do not support the forecast of enhanced precipitation amounts. The results show the OFA could contribute to the improvement of the general short-range weather forecast.     

虚拟地形建模中地物与地形匹配的算法研究

对于大比例尺条件下的地形环境仿真而言，采用贴2维纹理的方式表示地物已远远不能满足定位精度和可视化效果的需要，因为每个地物都是一个清晰可辨的3维实体了。在这种情况下地物模型能否与地形模型相匹配(即虚拟场景中的地物既不悬于地表之上也不陷入地表之下)将直接关系到视觉感受的逼真程度，以及在虚拟场景中对目标实施打击的精确程度。文中就如何实现地物模型与地形模型在数据层次上的匹配提出了一个解决方案，并对具体算法进行了详细阐述。实验结果表明了算法的正确性和实用性，由此说明匹配方案较为行之有效。     

电子地图中居民地的多尺度显示

探讨了多尺度的含义，并将居民地多尺度表达的研究限定在详细程度的变化上；阐述了电子地图中居民地多尺度表达的基本原理，即在保持原图的分布特征和疏密对比的情况下按照居民地自身的分类分级和重要性程度进行一定数量的取舍；建立了居民地多尺度显示的模型，根据此模型提出了采用二级邻近点判别法结合Voronoi图进行居民地要素的显示等级设置的方法，并进行了相应的实验，结果表明该方法对居民地的分布特征、密度对比和延伸方向均能较好的保持。     

基于降水气候强迫的一种地表径流估计方法

文中从地表水分平衡的物理机制出发 ,引进降水概率统计分布理论 ,推导出一种由降水气候强迫形成的次网格尺度非均匀径流率计算方法。应用于mosaic方案 ,可进一步计算区域平均径流及产流和汇流。试验证明 ,对于不同物理性质的地表而言 ,由于其土壤入渗能力的差异 ,相同降水气候强迫所能生成的径流量及其相对比值是不同的 ,例如干旱区与湿润区就有很大差异。同时 ,不同空间分布概率的降水量 ,不同站点的地表性质、土壤水力学条件等物理因素的千变万化 ,可使径流特征的空间分布具有很大变异性。因上述各种因素的综合影响 ,由降水气候强迫所形成的地表径流具有特定的非均匀分布是必然的。文中用实测资料验证了其可靠性与可行性     

NUMERICAL SIMULATION OF EXTREMELY HEAVY RAIN AND MESO-β SCALE LOW VORTEX IN INVERTED TYPHOON TROUGH*

Large-scale and mesoscale analyses are made for extremely heavy rain(EHR) and meso-β scale low vortex(MSLV) in Jiading District of Shanghai Municipality during 6-7 July 2001.It is shown that the EHR forms in the situation of northern westerly trough linking together with southern inverted typhoon trough at northwest side of the West Pacific Ocean subtropical high. Numerical simulation is made using a 21-layer improved REM(regional η coordinate model) for this course.The results show that the precipitation forms earlier than MSLV.and the strong convergence in wind velocity mate(WVM) triggers the strong precipitation.The formative reasons of WVM.especially the weak wind velocity center are discussed,and the formative mechanisms of the MSLV and EHR are discussed using high spatial and temporal resolution modeloutput physical fields.The results show that the heavy rain releases latent heat and warms the air column,and enhances the low level positive vorticity that existed before.Then it causes the formation of MSLV.There is a positive feedback mechanism between low vortex and precipitation,so CISK must be an important mechanism.     

Landslide hazard and risk mapping at catchment scale in the Arno River basin

We present the methodologies adopted and the outcomes obtained in the analysis of landslide risk in the basin of the Arno River (Central Italy) in the framework of a project sponsored by the Basin Authority of the Arno River, started in the year 2002 and completed at the beginning of 2005. In particular, a complete set of methods and applications for the assessment of landslide susceptibility and risk are described and discussed. A new landslide inventory of the whole area was realized, using conventional (aerial-photo interpretation and field surveys) and non-conventional methods (e.g. remote sensing techniques such as DInSAR and PS-InSAR). The great majority of the mapped mass movements are rotational slides (75%), solifluctions and other shallow slow movements (17%) and flows (5%), while soil slips, and other rapid landslides, seem less frequent everywhere within the basin. The relationships between landslide characteristics and environmental factors have been assessed through statistical analysis. As expected, the results show a strong control of land cover, lithology and morphology on landslide occurrence. The landslide frequency-size distribution shows a typical scaling behaviour already underlined in other landslide inventories worldwide. The assessment of landslide hazard in terms of probability of occurrence in a given time, based for mapped landslides on direct and indirect observations of the state of activity and recurrence time, has been extended to landslide-free areas through the application of statistical methods implemented in an artificial neural network (ANN). Unique conditions units (UCU) were defined by the map overlay of landslide preparatory factors (lithology, land cover, slope gradient, slope curvature and upslope contributing area) and afterwards used to construct a series of model vectors for the training and test of the ANN. Various different ANNs were selected throughout the basin, until each UCU was assigned a degree of membership to a susceptibility and a hazard class. Model validation confirms that prediction results are very good, with an average percentage of correctly recognized mass movements of about 85%. The analysis also revealed the existence of a large number of unmapped mass movements, thus contributing to the completeness of the final inventory. Temporal hazard was estimated via the translation of state of activity in recurrence time and hence probability of occurrence. The following intersection of hazard values with vulnerability and exposure figures, obtained by reclassification of digital vector mapping at 1:10,000 scale, lead to the definition of risk values for each terrain unit for different periods of time into the future. The final results of the research are now undergoing a process of integration and implementation within land planning and risk prevention policies and practices at local and national level.     

大比例尺城乡一体化土地调查综合技术的研究

本研究项目根据国家法规、规程和规定,以江阴市”数字国土”工程为研究对象,依靠3S现代测绘高新技术手段,对江阴市城镇1∶500、农村1∶1000进行地籍、地形和土地利用现状调查技术研究,建立城乡一体化地籍管理信息系统和基础地理信息系统,探索城乡一体化建设和维护更新等管理模式。