15 research outputs found
Object representations at multiple scales from digital elevation models
No full textAbstractIn the last decade landform classification and mapping has developed as one of the most active areas of geomorphometry. However, translation from continuous models of elevation and its derivatives (slope, aspect, and curvatures) to landform divisions (landforms and landform elements) is filtered by two important concepts: scale and object ontology. Although acknowledged as being important, these two issues have received surprisingly little attention.This contribution provides an overview and prospects of object representation from DEMs as a function of scale. Relationships between object delineation and classification or regionalization are explored, in the context of differences between general and specific geomorphometry. A review of scales issues in geomorphometry—ranging from scale effects to scale optimization techniques—is followed by an analysis of pros and cons of using cells and objects in DEM analysis. Prospects for coupling multi-scale analysis and object delineation are then discussed. Within this context, we propose discrete geomorphometry as a possible approach between general and specific geomorphometry. Discrete geomorphometry would apply to and describe land-surface divisions defined solely by the criteria of homogeneity in respect to a given land-surface parameter or a combination of several parameters. Homogeneity, in its turn, should always be relative to scale
Automated object-based classification of topography from SRTM data
No full textAbstractWe introduce an object-based method to automatically classify topography from SRTM data. The new method relies on the concept of decomposing land-surface complexity into more homogeneous domains. An elevation layer is automatically segmented and classified at three scale levels that represent domains of complexity by using self-adaptive, data-driven techniques. For each domain, scales in the data are detected with the help of local variance and segmentation is performed at these appropriate scales. Objects resulting from segmentation are partitioned into sub-domains based on thresholds given by the mean values of elevation and standard deviation of elevation respectively. Results resemble reasonably patterns of existing global and regional classifications, displaying a level of detail close to manually drawn maps. Statistical evaluation indicates that most of classes satisfy the regionalization requirements of maximizing internal homogeneity while minimizing external homogeneity. Most objects have boundaries matching natural discontinuities at regional level. The method is simple and fully automated. The input data consist of only one layer, which does not need any pre-processing. Both segmentation and classification rely on only two parameters: elevation and standard deviation of elevation. The methodology is implemented as a customized process for the eCognition® software, available as online download. The results are embedded in a web application with functionalities of visualization and download
Terrain Extraction in Built-Up Areas from Satellite Stereo-Imagery-Derived Surface Models: A Stratified Object-Based Approach
No full textVery high spatial resolution (VHSR) stereo-imagery-derived digital surface models (DSM) can be used to generate digital elevation models (DEM). Filtering algorithms and triangular irregular network (TIN) densification are the most common approaches. Most filter-based techniques focus on image-smoothing. We propose a new approach which makes use of integrated object-based image analysis (OBIA) techniques. An initial land cover classification is followed by stratified land cover ground point sample detection, using object-specific features to enhance the sampling quality. The detected ground point samples serve as the basis for the interpolation of the DEM. A regional uncertainty index (RUI) is calculated to express the quality of the generated DEM in regard to the DSM, based on the number of samples per land cover object. The results of our approach are compared to a high resolution Light Detection and Ranging (LiDAR)-DEM, and a high level of agreement is observed—especially for non-vegetated and scarcely-vegetated areas. Results show that the accuracy of the DEM is highly dependent on the quality of the initial DSM and—in accordance with the RUI—differs between the different land cover classes
A Proposal for Mapping Historic Irrigation Channels to Reveal Insights into Agro-Climatic Systems: A Case Study in Upper Austria. GI_Forum 2013 – Creating the GISociety|
No full textRecently, the remains of two historic irrigation channels were re-discovered in the Upper Austrian municipality of Regau. Since the current average precipitation in the region is sufficient to sustain a productive agricultural land use, the irrigation channels raise several questions related to climate variability. To verify different hypotheses such as the construction as a response to a changing climate or the assumed purpose of grassland irrigation, potential coherences are discussed. In addition, remote sensing techniques for the detection of hidden structures overprinted by physical and human activities are outlined. The analysis of available references enables a first assessment of the channels purpose. Several indicators such as the shape and incline of the remaining topographic imprints support the hypothesis of their irrigation function. Furthermore, the qualitative analysis of today’s agro-climatic conditions reveals the general vulnerability of the system to climate changes. Moreover, a dendrochronological analysis shows a phase of remarkable climate variability in conjunction with significant drying periods throughout the 3rd and 4th century. This may have posed a reason for the construction of the irrigation system. Further research is necessary to verify the possible alternative hypothesis, which suggests grassland fertilization as the main irrigation purpose. Therefore, a long term analysis of water nutrient contents is required. Moreover, the application of remote sensing techniques may help to identify the extent of the formerly irrigated area
An object-based approach for semi-automated landslide change detection and attribution of changes to landslide classes in northern Taiwan
Get PDFEarth observation (EO) data are very useful for the detection of landslides after triggering events, especially if they occur in remote and hardly accessible terrain. To fully exploit the potential of the wide range of existing remote sensing data, innovative and reliable landslide (change) detection methods are needed. Recently, object-based image analysis (OBIA) has been employed for EO-based landslide (change) mapping. The proposed object-based approach has been tested for a sub-area of the Baichi catchment in northern Taiwan. The focus is on the mapping of landslides and debris flows/sediment transport areas caused by the Typhoons Aere in 2004 and Matsa in 2005. For both events, pre- and post-disaster optical satellite images (SPOT-5 with 2.5 m spatial resolution) were analysed. A Digital Elevation Model (DEM) with 5 m spatial resolution and its derived products, i.e., slope and curvature, were additionally integrated in the analysis to support the semi-automated object-based landslide mapping. Changes were identified by comparing the normalised values of the Normalized Difference Vegetation Index (NDVI) and the Green Normalized Difference Vegetation Index (GNDVI) of segmentation-derived image objects between pre- and post-event images and attributed to landslide classes
Local variance for multi-scale analysis in geomorphometry
No full textAbstractIncreasing availability of high resolution Digital Elevation Models (DEMs) is leading to a paradigm shift regarding scale issues in geomorphometry, prompting new solutions to cope with multi-scale analysis and detection of characteristic scales. We tested the suitability of the local variance (LV) method, originally developed for image analysis, for multi-scale analysis in geomorphometry. The method consists of: 1) up-scaling land-surface parameters derived from a DEM; 2) calculating LV as the average standard deviation (SD) within a 3×3 moving window for each scale level; 3) calculating the rate of change of LV (ROC-LV) from one level to another, and 4) plotting values so obtained against scale levels. We interpreted peaks in the ROC-LV graphs as markers of scale levels where cells or segments match types of pattern elements characterized by (relatively) equal degrees of homogeneity. The proposed method has been applied to LiDAR DEMs in two test areas different in terms of roughness: low relief and mountainous, respectively. For each test area, scale levels for slope gradient, plan, and profile curvatures were produced at constant increments with either resampling (cell-based) or image segmentation (object-based). Visual assessment revealed homogeneous areas that convincingly associate into patterns of land-surface parameters well differentiated across scales. We found that the LV method performed better on scale levels generated through segmentation as compared to up-scaling through resampling. The results indicate that coupling multi-scale pattern analysis with delineation of morphometric primitives is possible. This approach could be further used for developing hierarchical classifications of landform elements
A Proposal for Mapping Historic Irrigation Channels to Reveal Insights into Agro-Climatic Systems: A Case Study in Upper Austria. GI_Forum 2013 – Creating the GISociety|
No full textRecently, the remains of two historic irrigation channels were re-discovered in the Upper Austrian municipality of Regau. Since the current average precipitation in the region is sufficient to sustain a productive agricultural land use, the irrigation channels raise several questions related to climate variability. To verify different hypotheses such as the construction as a response to a changing climate or the assumed purpose of grassland irrigation, potential coherences are discussed. In addition, remote sensing techniques for the detection of hidden structures overprinted by physical and human activities are outlined. The analysis of available references enables a first assessment of the channels purpose. Several indicators such as the shape and incline of the remaining topographic imprints support the hypothesis of their irrigation function. Furthermore, the qualitative analysis of today’s agro-climatic conditions reveals the general vulnerability of the system to climate changes. Moreover, a dendrochronological analysis shows a phase of remarkable climate variability in conjunction with significant drying periods throughout the 3rd and 4th century. This may have posed a reason for the construction of the irrigation system. Further research is necessary to verify the possible alternative hypothesis, which suggests grassland fertilization as the main irrigation purpose. Therefore, a long term analysis of water nutrient contents is required. Moreover, the application of remote sensing techniques may help to identify the extent of the formerly irrigated area
Assessment of multiresolution segmentation for delimiting drumlins in digital elevation models
Get PDFMapping or "delimiting" landforms is one of geomorphology's primary tools. Computer-based techniques such as land-surface segmentation allow the emulation of the process of manual landform delineation. Land-surface segmentation exhaustively subdivides a digital elevation model (DEM) into morphometrically-homogeneous irregularly-shaped regions, called terrain segments. Terrain segments can be created from various land-surface parameters (LSP) at multiple scales, and may therefore potentially correspond to the spatial extents of landforms such as drumlins. However, this depends on the segmentation algorithm, the parameterization, and the LSPs. In the present study we assess the widely used multiresolution segmentation (MRS) algorithm for its potential in providing terrain segments which delimit drumlins. Supervised testing was based on five 5-m DEMs that represented a set of 173 synthetic drumlins at random but representative positions in the same landscape. Five LSPs were tested, and four variants were computed for each LSP to assess the impact of median filtering of DEMs, and logarithmic transformation of LSPs. The testing scheme (1) employs MRS to partition each LSP exhaustively into 200 coarser scales of terrain segments by increasing the scale parameter (SP), (2) identifies the spatially best matching terrain segment for each reference drumlin, and (3) computes four segmentation accuracy metrics for quantifying the overall spatial match between drumlin segments and reference drumlins. Results of 100 tests showed that MRS tends to perform best on LSPs that are regionally derived from filtered DEMs, and then log-transformed. MRS delineated 97% of the detected drumlins at SP values between 1 and 50. Drumlin delimitation rates with values up to 50% are in line with the success of manual interpretations. Synthetic DEMs are well-suited for assessing landform quantification methods such as MRS, since subjectivity in the reference data is avoided which increases the reliability, validity and applicability of results
AGIT ‒ Journal für Angewandte Geoinformatik / Verfahren zur Implementierung eines Kartierungsdienstes für Rutschungen auf Basis von Fernerkundungsdaten und Nutzereinbindung
No full textIm Rahmen dieses Beitrags werden die technischen und nutzerzentrierten Analyseschritte zur Entwicklungen eines webbasierten Kartierungsdienstes für Rutschungen basierend auf Fernerkundungs- und Open-Source-Geodaten diskutiert. Der vorgestellte Dienst zielt darauf ab verschiedenste Akteure bei der Aktualisierung, Überwachung und Veröffentlichung von Rutschungsdaten sowie bei der Analyse der durch Rutschungen beeinträchtigten Infrastrukturen, wie zum Beispiel Straßennetzen, zu unterstützen. Zur Entwicklung eines Kartierungsdienstes für Rutschungen wurde ein iterativer und inkrementeller Ansatz der agilen Softwareentwicklung gewählt. Dieser Ansatz ermöglicht die direkte Einbindung des Nutzers in alle Phasen des Softwareentwicklungsprozesses. Dabei wird die Software in Einzelkomponenten entwickelt, wobei jede dieser Komponenten eine eigene und komplette Funktionalität darstellt. Verbesserungen an der Software werden schrittweise durchgeführt.In the presented paper the technical and user-centric analysis steps for the development of a web-based landslide mapping service are discussed. The generation of the service is based on remote sensing and open-source geodata. The service will support various stakeholders to monitor landslides, to update and publish landslide information, as well as to analyze affected infrastructures. For the service development, an iterative and incremental approach of agile software development is used. With the agile approach, the users are directly involved in all software development phases. Furthermore, the software is developed in single components and its enhancement is incrementally performed
Semi-Global Matching of Pléiades Tri-Stereo Imagery to Generate Detailed Digital Topography for High-Alpine Regions. GI_Forum|GI_Forum 2015 – Geospatial Minds for Society|
No full textNowadays, several sensors are capable of acquiring very high resolution (VHR) satellite images in stereo, and even in tri-stereo mode. These data can be efficiently exploited with photogrammetric methods, such as semi-global matching (SGM), to produce high quality 2.5D digital terrain information. Regarding the production of digital terrain models, since VHR (tri-)stereo satellite images are available at high temporal frequencies for nearly the whole globe, they can be considered an attractive alternative to restricted and expensive airborne laserscanning (ALS) data. In this study, SGM is applied to a Pléiades-1A image triplet, to generate an accurate and detailed 3D point cloud and a 2.5D digital surface model (DSM) for a high-alpine study area in South Tyrol with complex, snow- and ice-covered topography. Visual and quantitative comparison to an ALS reference DSM showed that there were only small elevation errors for large parts of the study area. Errors were higher in regions that were obscured by shade. This is one of the first studies demonstrating that SGM is not only capable of delivering reliable digital surface information for flat and hilly regions, but also for high-alpine areas with complex terrain
