Troposphere gradients from the ECMWF in VLBI analysis

Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02 and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a priori gradients are used.     

Road Surface Modeling and Representation from Point Cloud Based on Fuzzy Clustering

A scheme for an automatic road surface modeling from a noisy point cloud is presented. The normal vectors of the point cloud are estimated by distance-weighted fitting of local plane. Then, an automati...     

Correcting superconducting gravity time-series using rainfall modelling at the Vienna and Membach stations and application to Earth tide analysis

We demonstrate the possibility to improve the signal-to-noise ratio of superconducting gravity time-series by correcting for local hydrological effects. Short-term atmospheric events associated with heavy rain induce step-like gravity signals that deteriorate the frequency spectrum estimates. Based on 4D modeling constrained by high temporal resolution rain gauge data, rainfall admittances for the Vienna and Membach superconducting gravity stations are calculated. This allows routine correction for Newtonian rain water effects, which reduces the standard deviation of residuals after tidal parameter adjustment by 10%. It also improves the correction of steps of instrumental origin when they coincide with step-like water mass signals.     

浅析省级基础测绘数据在城市建模中的应用

利用基础测绘数据中房屋数据获取和编辑的方法,探讨1:10 000基础测绘数据中的建筑物在城市地理信息服务和建模中的应用以及目前基础测绘数据与城市建模数据间的差距.     

Skyline-based registration of 3D laser scans

Acquisition and registration of terrestrial 3D laser scans is a fundamental task in mapping and modeling of cities in three dimensions. To automate this task marker-free registration methods are required. Based on the existence of skyline features, this paper proposes a novel method. The skyline features are extracted from panoramic 3D scans and encoded as strings enabling the use of string matching for merging the scans. Initial results of the proposed method in the old city center of Bremen are pre-sented.     

三维激光扫描仪在惠泉变电站三维模型构建中的应用

文中通过利用地面三维激光扫描仪获取的空间数据,进行了惠泉变电站三维空间地物建模研究。首先探讨点的密度对数据采集的影响;然后通过整体匹配纠正并对原始测量数据进行拼接配准;最后建立了三维表面模型。通过研究发现利用三维激光扫描技术可以快速建立三维空间的可视化模型,解决了传统的测量仪器与测量方法在变电站等特殊领域的不足。为能够实现变电站资源的数字化,提供了一个变电站三维模型构建的新方向。     

GIS三维动态符号库的研究与开发

本文探讨了与GIS三维动态符号库相关的概念、分类及三维图形变换等基础理论;搭建了基于Java3D的GIS三维动态符号库开发平台;研究了3DMAX建模、三维动态符号库、建筑物内部场景展示等关键技术;开发了GIS三维动态符号库.     

基于三棱柱的三维地质体建模及可视化研究

建立可视化的三维地质模型是地质信息可视化的一个研究重点,能够为各种地质现象描述提供科学依据。本文主要研究了基于三棱柱的模型构造,提出了三棱柱的改进数据结构和切割的构形以及算法,并且在VC6.0环境下,采用OpenGL作为图形开发工具,实现了三维地质体的可视化,解决了地质体剖切和基坑开挖等问题。     

多频率多极化地表辐射参数化模型

发展了针对对地观测系统被动微波辐射计AMSR-E应用的裸露地表辐射模型。首先，利用1993年法国INRA地面试验数据对AIEM在宽波段高频率和大角度的辐射信号模拟能力进行评价。验证结果表明，AIEM模型模拟值与地面实测数据吻合很好，说明AIEM模型能很好模拟宽波段和大角度的辐射信号。在此基础上，用AIEM模型建立了一个针对AMSR-E传感器参数配置．包含各种地表粗糙度和介电特性的裸露地表辐射模拟数据库。利用AIEM模拟数据和地面实测数据对目前人们使用的半经验地表模型进行了比较和分析，发展了多频率多极化的地表辐射参数化模型——Qp模型。该模型中，地表粗糙度对辐射信号的影响通过粗糙度参数Qp来表示。参数Qp可简单表示为均方根高度与相关长度的比值（s／l）。从Qp模型与AIEM模型模拟的发射率比较结果来看，它们之间的绝对误差很小，不超过10^-3因而，本文发展的参数化模型可用作模拟地表辐射的前向模型，如用于估算AMSR-E传感器的亮温值，同时模型的发展有利于提高人们对辐射机制的理解和认识。     

基于UML的农用地估价信息系统建模与实现

根据农用地估价的基本原理和方法,以ComGIS为系统开发平台,利用UML技术,从系统整体设计入手,提出了采用多层次用例描述法建立农用地估价信息系统(ALEIS)用例模型的过程,在此基础上介绍了ALEIS设计、编码与测试,最后提出了ALEIS的特点与发展趋势。在农用地估价信息系统开发过程中,利用UML对系统进行建模分析能够取得较好的效果。