WZD94中国重力大地水准面研究

利用我国实测重力值计算完成了全国５＇×５＇格网平均空间重力异常，并结合重力场模型ＷＤＭ９４，利用国内外最新发展起来的快速谱算法确定了我国高分辨率５＇×５＇重力大地水准面ＷＺＤ９４。     

Comment on Sjöberg (2006) “The topographic bias by analytical continuation in physical geodesy” J Geod 81(5):345–350

The analytical, or harmonic, downward continuation of the external gravity potential into the topographic masses gives rise to a bias, which is called the analytical (downward) continuation (ADC) bias (Ågren in J Geod 78:314–332, 2004a) or the topographic bias (Sjöberg in J Geod, 2006). In Sjöberg (J Geod, 2006), a proof is presented that this bias is exactly equal to a simple two-term expression, which depends only on the topographic height and density in the evaluation point P. The expression is simple and inexpensive to evaluate. In this paper, we wish to question the validity of the expression given in Sjöberg (J Geod, 2006) for realistic terrains. The topographic bias is commonly defined as the difference between the true (internal) and the analytically downward continued external geopotential, evaluated at sea level. Typically both are evaluated as external or internal spherical harmonic (SH) expansions, which may however not always converge. If they do converge, they have been well known in the literature (e.g., Ågren (J Geod 78:314–332, 2004a), Wang (J Geod 71:70–82, 1997)) to produce a bias that contains additional terms over and beyond the simple expression. Below we analyze the additional terms that arise when applying the method to realistic terrains. Also, for realistic terrains, analytical downward continuation may not even be strictly possible. In practice, for discrete data sets, it is always possible, but then, an implicit smoothing of the terrain, or terrain potential, always takes place.     

Ripe for the picking? Dataset maturity assessment based on temporal dynamics of feature definitions

Map databases traditionally capture snapshot representations of the world following strict data collection and representation guidelines. The content of these map databases is often assessed using data quality metrics focusing on accuracy, completeness and consistency. The success of volunteered geographic information, supporting evolving representations of the world based on fluid guidelines, has rendered these measures insufficient. In this paper, we address the need to capture the variability in quality of a map database. We propose a new spatial data quality measure – dataset maturity – enabling assessment of the database based on temporal trends in feature definitions, specifically geometry-type definitions. The proposed measure can be (1) efficiently used to identify feature definition patterns reflecting community consensus that could be formalised in community guidelines and (2) deployed to identify regions that would benefit from increased editorial activity to achieve greater map homogeneity. We demonstrate the measure based on the content of the OpenStreetMap database in four regions of the world and show how the proposed dataset maturity measure captures a distinct quality of the datasets, distinct to data completeness and consistency.     

三峡水库蓄水对地壳形变及大地水准面的影响

利用资源三号(ZY-3)高分辨率遥感影像提取三峡库区水体数据,通过负荷格林函数积分模型法计算出三峡水库蓄水过程中水体对地壳形变及对大地水准面的影响。研究发现:1三峡库区近岸地壳垂直形变与水库水位呈负相关关系,大地水准面与水库水位呈正相关关系;水位上升,长江近岸地面水平向内形变,方向指向江心;2三峡水库蓄水造成的地壳垂直形变最大可达35mm左右,大地水准面形变最大值在8mm左右,而对库区地壳水平形变影响不超过0.5mm;3出现形变最大值的地点是忠县环湾一带,而并非是三峡大坝周边。     

海岸带地区SPOT-5遥感影像无控制点正射校正方法

本文利用ENVI遥感软件处理平台,针对海岸带地区影像特点,对传统的SPOT-5遥感影像正射校正流程进行改进,主要有:增加SPOT传感器辐射校正;在影像融合前,使用伪正射校正代替几何校正;利用GDEM数据代替传统的DEM测量数据及野外测点数据;使用Google Earth Bridge功能检验校正结果精度。结果表明:经过改进的无控制点正射校正流程可有效减少人为误操作产生的误差,降低了正射校正的难度,提高了影像处理的效率,拓宽了影像检验的思路。正射校正影像精度符合研究要求,取得较为满意的结果。     

Geoid deformation and elevation influence caused by building loading

The paper studies the ground vertical deformation and the geoid undulation caused by loading of neighboring buildings, based on the loading tides theory. The influence on elevation is also considered. The results show that the ground vertical deformation and the geoid undulation both reach millimeter magnitude. Therefore, it is obvious that the building loading significantly affects the precise engineering surveying, and it must be seriously considered in application.     

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