How does co-registration affect geomorphic change estimates in multi-temporal surveys?

ABSTRACT

High-Resolution Topography (HRT) data sets are becoming increasingly available, improving our ability and opportunities to monitor geomorphic changes through multi-temporal Digital Terrain Models (DTMs). The use of repeated topographic surveys enables inferring the sediment dynamics of hazardous geomorphic processes such as floods, debris flows, and landslides, and allows us to derive important information on the risks often associated with these processes. The topographic surveying platforms, georeferencing systems, and processing tools have seen important developments in the last two decades, in particular Light Detection And Ranging (LiDAR) technology used in Airborne Laser Scanning (ALS) and Terrestrial Laser Scanning (TLS). Moreover, HRT data, produced through these techniques, changed a lot in terms of point cloud density, accuracy and precision over time. Therefore, old “legacy” data sets and recent surveys can often show comparison problems, especially when multi-temporal data are not homogeneous in terms of quality and uncertainties. In this context, data co-registration should be used to guarantee the coherence among multi-temporal surveys, minimizing, on stable areas, the distance between corresponding points acquired at different epochs. Although several studies highlight that this process is fundamental to properly compare multi-temporal DTMs, it is often not addressed in LiDAR post-processing workflows. In this paper we focus on the alignment of multi-temporal surveys in a topographically complex and rugged environment as the Moscardo debris-flow catchment (Eastern Italian Alps), testing various co-registration methods to align multi-temporal ALS point clouds (i.e. years 2003, 2009 and 2013) and the derived DTMs. In particular, we tested the pairwise registration with manual correspondences, the Iterative Closest Point (ICP) algorithm and a mathematical model that allows aligning simultaneously a generic number of point clouds, the so-called Generalized Procrustes Analysis (GPA), also in its GPA-ICP variant. Then, to correct the possible small inaccuracies generated from the gridding interpolation process, a custom-developed DTM co-registration tool (GRD-CoReg) was used to align gridded data. Both alignment phases (i.e. at point cloud and DTM level) proved to be fundamental and allowed us to obtain proper and reliable DTMs of Difference (DoDs), useful to quantify the debris mobilized and to detect the spatial and temporal patterns of catchment-scale erosion and deposition. The consistency of DoDs data was verified through the comparison between the erosion estimate of DoDs and the volumes of debris-flow events measured by the monitoring station close to the Moscardo torrent catchment outlet. The GPA-ICP algorithm followed by the GRD-CoReg tool proved to be the most effective solution for improving DoDs results with a decrease of systematic trend due to vertical and horizontal uncertainties between surveys, especially at steep slopes. The net volume difference (i.e. the sediment output from the catchment) of the 2003–2013 period changed from 3,237,896 m³ to 135,902 m³ in DoDs obtained from not co-registered and co-registered DTMs. The volume of debris flows measured at the catchment outlet during the same time interval amounts to 169,660 m³. The comparison with debris-flow volume measures at the monitoring station shows, therefore, that the DTMs obtained from the co-registration processes generate more reliable DoDs than those obtained from the raw DTMs (without the alignment).     

Creation of DTM with ASTER Data and Statistical Verification of the Accuracy of the Model (Western Peloponnese,Greece)

Abstract

In this paper we present the use of ASTER data for the creation of a Digital Terrain Model (DMT) of high accuracy. Using a stereo pair of ASTER satellite images with 15m resolution we created two DMTs: one with a 30m pixel size and another one with a 15m pixel size. Then we made a statistical verification of the two DTMs accuracy. We created another DTM with 30m pixel size from digitized contours of 1:50000 scale topographic maps. We first made an optical comparison of the two DTMs with 30m pixel size. Then we subtracted the two DTMs and we presented their difference. Finally, we verified the DTMs accuracy using 68 points of a well‐known elevation. All the results demonstrated that DTMs derived from ASTER data have very good accuracy.     

数字环境下制图综合概念和方法的拓展

制图综合是地图学的一个核心和难点问题。随着GIS应用领域的拓展和地理空间信息栅格的提出，需要研究多尺度、多分辨率或不同详细程度的空间地理数据的自动生成问题，以满足GIS多层次应用与决策的需求，而这正是制图综合在数字环境下所要面对的新问题。因此，数字环境下制图综合不应该再仅仅局限于图形综合的概念，而且还应该包括基于地图数据库的数据集成、数据表达、数据分析和数据库派生的数据综合，更侧重于GIS环境下空间数据的多尺度表达以及数字信息处理的问题。     

GIS中的地理信息综合

ＧＩＳ中地理信息综合功能的研究和开发是当的ＧＩＳ技术进步与应用发展所面临的一个新挑战。首先研究了ＧＩＳ中地理信息综合功能的意义、基本内容及其实现途径,然后介绍了作者所提出的基于分形分析的自动综合算法和实例,最后分析了ＧＩＳ地理信息综合功能研究中需要进一步解决的问题。     

Electronic Theses and Dissertations (ETDs), GIS,and Remote Sensing: The West Virginia University Example

Abstract

Remote sensing and geographic information system (GIS) scientists and educators in general are utilizing global web sources for information of the latest developments in the use of satellite and GIS approaches, as well as to understand more fully environmental and natural resources processes in various geographic settings. West Virginia University (WVU) has embarked on a pioneering approach (as only the second university worldwide) to archive graduate theses and dissertations in electronic format with worldwide web access. This study illustrates the type of remote sensing and GIS research available through WVU's worldwide web ETD archive, and its potential uses by educators at a variety of levels of the education system for understanding remote sensing and GIS methodologies, as well as environmental and natural resource processes. Keywords: Geographic Information Systems (GIS), remote sensing, West Virginia University, Electronic Thesis and Dissertation (ETD).     

Fourier-based multi-scale representation and progressive transmission of cartographic curves on the internet

ABSTRACT

Automatic generation of multi-scale representations from the same spatial data source has been the research focus in map generalization for a long time. Based on the Fourier technique, this paper proposes a continuous, multi-scale representation model for progressive transformation of cartographic curves on the Internet. In our method, all the curves, whether closed or open, are depicted as periodical functions which are further expressed as Fourier series. The convergence degrees of the Fourier series are explored for different kinds of curves, and truncating frequencies are derived based on the similarity between the original and reconstructed curves. Using information theory and the Radical Law in cartography, the relationship between map scales and Fourier frequencies is established. Based on the proposed multi-scale model, we also introduce the principles and implementation of a progressive transmission method. Our method is evaluated using the contours from a topographic map. The results show that our model is a valid approach to multi-scale representation of cartographic curves.     

GEOEssential – mainstreaming workflows from data sources to environment policy indicators with essential variables

ABSTRACT

When defining indicators on the environment, the use of existing initiatives should be a priority rather than redefining indicators each time. From an Information, Communication and Technology perspective, data interoperability and standardization are critical to improve data access and exchange as promoted by the Group on Earth Observations. GEOEssential is following an end-user driven approach by defining Essential Variables (EVs), as an intermediate value between environmental policy indicators and their appropriate data sources. From international to local scales, environmental policies and indicators are increasingly percolating down from the global to the local agendas. The scientific business processes for the generation of EVs and related indicators can be formalized in workflows specifying the necessary logical steps. To this aim, GEOEssential is developing a Virtual Laboratory the main objective of which is to instantiate conceptual workflows, which are stored in a dedicated knowledge base, generating executable workflows. To interpret and present the relevant outputs/results carried out by the different thematic workflows considered in GEOEssential (i.e. biodiversity, ecosystems, extractives, night light, and food-water-energy nexus), a Dashboard is built as a visual front-end. This is a valuable instrument to track progresses towards environmental policies.     

A comparison between analytical aerial photogrammetry,laser scanning,total station and global positioning system surveys for generation of digital terrain model

The present paper compares between four data sources for creating digital terrain models (DTMs), based on analytical aerial photogrammetry, laser scanning, total station (TS) and global positioning system surveys. The case study presents the comparative results obtained using the methods listed above. After obtaining the ground coordinates of points using each method, DTMs were created using Surfer Software to establish comparison consistency. To check accuracy of each method used, a series of 100 independent points were collected at random positions over the case study area using the TS for horizontal position and a digital level for elevation. The comparison of the results of the methods was performed based on accuracy and efficiency aspects. The results have shown that TS and terrestrial laser scanners (TLSs) could represent precise, effective and rapid solutions to produce economical and accurate DTMs. Also, using TLSs allow more various possibilities of data representation.     

Urban expansion in Xiongan New Area since 1975

Abstract

Although urban expansion has been extensively studied at different scales in China, relatively little attention has been paid to the county scale. Xiongan New Area (XNA) was selected as the study area and its urban expansion processes from 1975 to 2017 were retrieved using remote sensing and GIS technology, and its spatial-temporal characteristics of urban expansion were revealed from the aspects of basic characteristics of urban expansion, urban spatial morphological evolution, interactions of urban lands, and assessments of the imbalanced degree of population-land urbanization. Results indicated that urban lands in XNA expanded significantly. Cultivated lands were the first land source for urban expansion. Urban lands mainly adopted the edge-expansion, which rendered the urban fringes to be complex and irregular. The interaction of three counties in XNA was strengthened successively, especially after the implementation of the ‘New Urbanization’ strategy. Population-land urbanization was inharmonious but has improved from moderate to mild imbalance.     

基于小波分析的地貌多尺度表达与自动综合

基于小波多分辨率分析原理，给出了一种尺度依赖的地表形态抽象与表达方法。基于该方法研究了多尺度的地貌自动综合，提出了利用小波系数的范数比作衡量相应尺度综合程度的数量化指标，并结合实例予以说明。     

Rule‐based Integration of Remotely‐sensed Data and GIS for Land Cover Mapping in NE Costa Rica

Abstract

A classification method was developed for mapping land cover in NE Costa Rica at a regional scale for spatial input to a biogeochemical model (CENTURY). To distinguish heterogeneous cover types, unsupervised classifications of Landsat Thematic Mapper data were combined with ancillary and derived data in an iterative process. Spectral classes corresponding to ground control types were segregated into a storage raster while ambiguous pixels were passed through a set of rules to the next stage of processing. Feature sets were used at each step to help sort spectral classes into land cover classes. The process enabled different feature sets to be used for different types while recognizing that spectral classification alone was not sufficient for separating cover types that were defined by heterogeneity. Spectral data included the TM reflective bands, principal components and the NDVI. Ancillary data included GIS coverages of swamp extents, banana plantation boundaries and river courses. Derived data included neighborhood variety and majority measures that captured texture. The final map depicts 18 land cover types and captures the general patterns found in the region. Some confusion still exists between closely related types such as pasture with different amounts of tree cover.     

基于路段重要度评价的道路网自动制图综合研究

道路网自动综合是GIS研究的重要基础理论问题。顾及道路重要性对路网制图综合的影响,采用基于对偶拓扑的复杂网络理论构建城市路网对偶拓扑模型,并基于该路网模型建立路段重要度评价方法,进而提出一种基于路段重要度评价的路网自动制图综合方法。实验表明,该方法能够有效地完成不同比例尺下路网的自动综合。     

面向特征的网络空间点群要素自动综合方法

网络空间信息可视化对揭示网络空域规律、促进网络空间认知具有重要意义。将网络空间节点与拓扑关系直接可视化的视图中存在大量的点重合和线交叉,目前已有的网络节点布局算法、集束边技术、骨干网提取和网络路由拓扑多尺度表达等方法能够优化视图效果,但在网络的微观结构上,对保持网络空间点群要素的特征信息关注不够。通过分析并量化网络空间点群要素的各类特征信息,提出了一种基于层次聚类的要素聚合方法和一种基于节点重要性度量的要素选取方法,以自动综合的方式对网络空间点群要素进行综合。实验结果表明,该方法能够保持网络空间点群要素的空间特征,为定量表达网络空间特征、加速生成视觉效果良好的网络空间地图提供基础数据综合方法。     

Paleoart: Visions of the Prehistoric Past

Abstract

Cartography in general, and building solid landscape models in particular, requires an interdisciplinary set of skills in order to be done well. Traditional handcrafted construction methods provide quality results, but are extremely labour-intensive and therefore costly. Modern methods using digital terrain models (DTMs) and computer numerical control (CNC) milling are fast and accurate, but the finished models are visually less than optimal. Solutions are proposed using DTMs and CNC milling to create landscape models in which the initial shaping is done mechanically and the fine details are carved by hand. This ‘balanced approach’ to landscape modelling combines the time- and cost-advantages of modern digital technology with the quality of traditional handcrafted techniques resulting in highly accurate landscape models which still retain the artistic ‘feel’ of the human touch.     

Places of the Holocaust: Towards a model of GIS of place

Progress toward developing a GIS of place can only follow from an understanding of what place is, and this understanding draws on geographical theory. Here—following Agnew, Tuan, and others—we consider place as being made up of three components—location, locale, and sense of place—which are recognizable at multiple scales and vary historically as a product of social and political processes. Using the testimonies of two survivors of the Holocaust, we sketch the components of a model for a GIS of place that allows for this theory of place to be visualized and analyzed. The model is, crucially, both multi‐scalar and sensitive to uncertainty, as a GIS of place needs to be able to zoom in and out of the different scales at which place is experienced, as well as capture both uncertain data and uncertainty as data. We see potential in the representations proposed for scaling up from the anecdotal to the general in the sense that any narrative can be grouped and classified according to places and scales as shown here. The challenge in developing a GIS of place along the lines we propose here is to design a new set of functionalities that can do so.     

Effects of detailed soil spatial information on watershed modeling across different model scales

Hydro-ecological modelers often use spatial variation of soil information derived from conventional soil surveys in simulation of hydro-ecological processes over watersheds at mesoscale (10–100 km²). Conventional soil surveys are not designed to provide the same level of spatial detail as terrain and vegetation inputs derived from digital terrain analysis and remote sensing techniques. Soil property layers derived from conventional soil surveys are often incompatible with detailed terrain and remotely sensed data due to their difference in scales. The objective of this research is to examine the effect of scale incompatibility between soil information and the detailed digital terrain data and remotely sensed information by comparing simulations of watershed processes based on the conventional soil map and those simulations based on detailed soil information across different simulation scales. The detailed soil spatial information was derived using a GIS (geographical information system), expert knowledge, and fuzzy logic based predictive mapping approach (Soil Land Inference Model, SoLIM). The Regional Hydro-Ecological Simulation System (RHESSys) is used to simulate two watershed processes: net photosynthesis and stream flow. The difference between simulation based on the conventional soil map and that based on the detailed predictive soil map at a given simulation scale is perceived to be the effect of scale incompatibility between conventional soil data and the rest of the (more detailed) data layers at that scale. Two modeling approaches were taken in this study: the lumped parameter approach and the distributed parameter approach. The results over two small watersheds indicate that the effect does not necessarily always increase or decrease as the simulation scale becomes finer or coarser. For a given watershed there seems to be a fixed scale at which the effect is consistently low for the simulated processes with both the lumped parameter approach and the distributed parameter approach.     

Developing spatially and thematically detailed backdated maps for land cover studies

ABSTRACT

Global or regional land cover change on a decadal time scale can be studied at a high level of detail using the availability of remote sensing data such as that provided by Landsat. However, there are three main technical challenges in this goal. First, the generation of land cover maps without reference data is problematic (backdating). Second, it is important to maintain high accuracies in land cover change map products, requiring a reasonably rich legend within each map. Third, a high level of automation is necessary to aid the management of large volumes of data. This paper describes a robust methodology for processing time series of satellite data over large spatial areas. The methodology includes a retrospective analysis used for the generation of training and test data for historical periods lacking reference information. This methodology was developed in the context of research on global change in the Iberian Peninsula. In this study we selected two scenes covering geographic regions that are representative of the Iberian Peninsula. For each scene, we present the results of two classifications (1985–1989 and 2000–2004 quinquennia), each with a legend of 13 categories. An overall accuracy of over 92% was obtained for all 4 maps.     

Model development for subsurface organic compound vapor diffusion using geographic information systems: A feasibility assessment

Abstract

The feasibility of using a geographic information system (GIS) to evaluate the subsurface transport of volatile organic compounds (VOCs) is evaluated. A GIS analysis based on selected soil properties and a flow path model were used to demonstrate the visualization of a probable path taken by diffusing VOC vapors in the vadose zone. The model uses soil properties such as texture, organic matter content, water content, bulk density, and permeability as path finding indices. The values of the soil properties used in the validation of this model were obtained from the respective County Soil Survey Reports. The various combinations of these soil properties resulted in deviations from the anticipated path taken by the diffusing organic vapors as they migrated through the subsurface.

The model was evaluated using two soil systems and estimated diffusion coefficients. A proportionality constant (k) was calculated and used in conjunction with the assigned soil property values in the calculation of diffusion coefficients (Df) for trichloroethylene (TCE) vapors for each soil system. For each case, the model depicts the probable path taken by the VOC vapors as being the route through the soils having characteristics most favorable for chemical migration. Specifically, the soils along the predicted flow path have combinations of high moisture contents, low bulk densities, clay and organic matter contents as well as higher porosity and permeability than soils along any other possible flow path in the given soil systems.     

Digital Terrain Model Resolution and its Influence on Estimating the Extent of Rockfall Areas

As rockfall can cause a great deal of damage, it is essential to know its spatial propagation. Rockfall models are sensitive to the resolution of input data, i.e. the Digital Terrain Model (DTM) used. Nowadays, high resolution elevation data are available area‐wide from airborne laser scanning (ALS). However, rockfall models are designed for analysis on a certain scale, which means that high resolution input might not necessarily improve model results (e.g. for regional scale studies). Our aim is to estimate the reach of rockfall by analysing different input resolutions of an ALS DTM. The presented empirically–based model, implemented in Python 2.7, is a modified version of the zenital method including an iterative random walk trajectory model, which is designed for rockfall hazard assessment at the regional scale. Trajectories and rockfall probability maps are generated for selected DTM input resolutions. The comparison shows that high resolution DTMs do consider local topography better and thus lead to more realistic results than low resolution DTMs.