Xiangtao Fan

A digital earth prototype system: DEPS/CAS

Abstract Digital Earth is an information expression of the real Earth, and is a new way of understanding the Earth in the twenty-first century. This paper introduces a Digital Earth Prototype System (DEPS) developed at the Chinese Academy of Sciences (CAS) and supported by the Knowledge Innovation Program of the Chinese Academy of Sciences. Discussions are made to the theoretical model and technical framework of the Digital Earth, and its related key technologies on spatial information processing, spatial data warehouse technology, virtual reality technology, high-performance and parallel computing. The DEPS consists of seven sub-systems including the spatial data, metadata, model database, Grid geoscience computing, spatial information database, maps service and virtual reality. Meanwhile, we developed a series of application systems such as the environment monitoring for the Olympic Games 2008 in Beijing, natural disasters evaluation, digital city, digital archeology, Asia regional aerosol and climate change. The DEPS/CAS displayed the application ability and potential of the Digital Earth in three levels: the global, national and regional.

Methodology for geographical data evolution: three-dimensional particle-based real-time snow simulation with remote-sensing data

Abstract Even if current remote-sensing technology provides more spatial information, remote-sensing data with discontinuous spatial and temporal resolutions are still not adequate. To compensate for the missing data of remote sensing, we create a methodology for geographical data evolution from a snow simulation. Numerical algorithms based on snow simulation and environmental phenomenon interaction algorithms are presented to evolve remote-sensing data in a virtual environment. Specifically, the methodology involves the establishment of a suitable three-dimensional data model and the discrete numerical expressions of geological or geographical phenomena. The modeling solution of environmental phenomena reactions is based on remote-sensing data. This computational simulation does not merely generate new data and spatial resolutions at a given time, but it offers multiscale environmental characteristics of the Earth and presents reference for its future scene.

Vertical accuracy assessment of freely available digital elevation models over low-lying coastal plains

The frequency of coastal flood damages is expected to increase significantly during the twenty-first century as sea level rises in the coastal floodplain. Coastal digital elevation model (DEM) data describing coastal topography are essential for assessing future flood-related damages and understanding the impacts of sea-level rise. The Shuttle Radar Topography Mission (SRTM) and Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model (ASTER GDEM) are currently the most accurate and freely available DEM data. However, an accuracy assessment specifically targeted at DEMs over low elevation coastal plains is lacking. The present study focuses on these areas to assess the vertical accuracy of SRTM and ASTER GDEM using Ice, Cloud, and land Elevation Satellite, Geoscience Laser Altimeter System (ICESat/GLAS) and Real Time Kinematic (RTK) Global Positioning System (GPS) field survey data. The findings show that DEM accuracy is much better than the mission specifications over coastal plains. In addition, optical remote sensing image analysis further reveals the relationship between DEM vertical accuracy and land cover in these areas. This study provides a systematic approach to assess the accuracy of DEMs in coastal zones, and the results highlight the limitations and potential of these DEMs in coastal applications.

Fusion of high-resolution remote sensing images based on a/spl acute/ trous wavelet algorithm

There are some problems not to be resolved very well, when we merge images by the wavelet transform method. One problem is how many levels the original images should be decomposed to, in order to make fusion images obtain more information. Other problem is how to reduce the spectral distortions of the fusion images more efficiently, when we enhance the spatial resolution of the low-resolution images. We rightly select the number of wavelet decomposition levels by computing entropy of the fusion images. When performing wavelet reconstruction, we introduce the local correlation coefficient and set up the different thresholds at different levels of wavelet decomposition, in order to reduce the spectral distortions of the fusion images. In our experiment we merge three multispectral images with a panchromatic image of Quickbird data by our method. The results demonstrate that our method is a good fusion method to increase information and reduce spectral distortions.

Simulated impacts of 3D urban morphology on urban transportation in megacities: case study in Beijing

Urban morphology and morphology change and their impacts on urban transportation have been studied extensively in planar urban space. The essential feature of urban space, however, is its three-dimensionality (3D), and few studies have been conducted from a 3D perspective, overly limiting the accuracy of studies on the relationships between urban morphology and transportation. The aim of this paper is to simulate the impacts of 3D urban morphologies on urban transportation under the Digital Earth framework. On the basis of the principle that population distribution and movement are largely confined by 3D urban morphologies, which affect transportation, high spatial resolution remote sensing imagery and a thematic vector data-set were used to extract urban morphology and transportation-related variables. With a combination of three research methods – factor analysis, spatial regression analysis and Euclidean allocation – we provide an effective method to construct a simulation model. The paper indicates three general results. First, building capacity in the urban space has the most significant impact on traffic condition. Second, obvious urban space otherness, reflecting both use density characteristics and functional characteristics of urban space, mostly results in heavier traffic flow pressure. Third, no single morphology density indicator or single urban structure indicator can reflect its contribution to the pressure of traffic flow directly, but a combination of these different indicators has the ability to do so.

Study on the interconnection and interoperability between urban 3D visualization and geographic information system

Urban 3D visualization is an exciting domain, with a growing number of important applications. Researches on VR (Virtual Reality) and GIS (Geographic Information System) provide strong technological support for real-time visualization of urban scenery. This paper focuses on the interconnection and interoperability between urban 3D visualization technology and GIS, including a scheme to exchange data between the GIS database and rendering engines for visualization, navigation and manipulation. A virtual scene of IRSA (Institute of Remote Sensing Applications), based in Beijing, China, which shows a fusion between urban 3D visualization and GIS is presented and realized.

Augmented virtual environment: fusion of real-time video and 3D models in the digital earth system

ABSTRACT An Augmented virtual environment (AVE) is concerned with the fusion of real-time video with 3D models or scenes so as to augment the virtual environment. In this paper, a new approach to establish an AVE with a wide field of view is proposed, including real-time video projection, multiple video texture fusion and 3D visualization of moving objects. A new diagonally weighted algorithm is proposed to smooth the apparent gaps within the overlapping area between the two adjacent videos. A visualization method for the location and trajectory of a moving virtual object is proposed to display the moving object and its trajectory in the 3D virtual environment. The experimental results showed that the proposed set of algorithms are able to fuse multiple real-time videos with 3D models efficiently, and the experiment runs a 3D scene containing two million triangles and six real-time videos at around 55 frames per second on a laptop with 1GB of graphics card memory. In addition, a realistic AVE with a wide field of view was created based on the Digital Earth Science Platform by fusing three videos with a complex indoor virtual scene, visualizing a moving object and drawing its trajectory in the real time.

Numerical simulation of the evolutionary process of Danxia landforms

Danxia landforms are defined as a landscape type that developed in red terrestrial clastic rocks generally with near-horizontal strata. Lithology, vertical joint sets, tectonic history, and rainfall play important roles in shaping Danxia landforms, leading to increased difficulty and complexity in quantitatively understanding their evolution. Integrating the factors mentioned above, this study represents the first attempt to investigate the evolutionary process of Danxia landforms using a numerical simulation. Parameters used in this study were employed from earlier studies on Danxia Mountain in southeastern China. The results quantitatively present a complete dynamic course shaping Danxia landforms that could not be seen from field observation alone. The process arises from interactions between tectonics and fluvial erosion and displays typical characteristics of Danxia landforms in different evolutionary stages. The results also show that the features of fractures and joints have significant constraints on the evolutionary process. Through comparative analysis of the earlier conceptual results and our simulation, we conclude that the model used in this study can reasonably represent the typical, physical formation process of Danxia landforms. Although the model is robust and thus might not be precise, our results still reveal the interesting dynamic behavior shaping Danxia landforms.

Accuracy assessment of GPS navigation augmented by SAR and LiDAR-derived Digital Elevation Models

Remotely sensed Digital Elevation Models (DEM) can be used to augment a standalone Global Positioning System (GPS) by adding an extra range observation which measures the distance to the Earth centre. This method so called height aiding can reduce the number of GPS satellites required to get a 3D position fix from four to three and hence improve the performance of the GPS navigation algorithm in terms of accuracy, reliability and availability. Up until now, the accuracy of height aided GPS navigation using higher resolution Synthetic Aperture Radar (SAR) and Light Detection and Ranging (LiDAR)-derived elevation data has not been fully evaluated in a broad spectrum of navigation scenarios. This article provides a robust and accurate analysis on how much range error is introduced by height aiding using 5 m spacing SAR and 1 m spacing LiDAR-derived DEMs under in-car and personal navigation situations. Based on the experimental results obtained from both dynamic and static tests, suggestions have been made on what level of vertical and positional accuracy can be achieved as well as the related DEM quality issues for navigation purposes.

Flood modeling and inundation risk evaluation using remote sensing imagery in coastal zone of China

Global climate change has caused sea level rise, and one of the most extremely consequences are the increased frequency and hazards of the storm surge disasters, therefore, how to effectively assess the risk of storm surge disaster is of importance to hazard reduction and mitigation. However, the storm surge forecast models have complex parameters, which computational inefficiency. Traditional large-scale assessment usually takes elevation-area method based on GIS software, which result in large errors. The present study is attempted to: (1) Select proper two-dimensional hydraulic storm surge inundation model. This model not only has the physical realism but simple and efficient. (2)The present study will focus on the method to extract the required surface parameters based on the remote sensing data to integrate remote sensing data into the model. This project aims to provide the theoretical basis and methodologies for flood risk assessment in coastal zone of China.