Influence of different digital terrain models (DTMs)on alpine permafrost modeling

The thawing of alpine permafrost due to changes in atmospheric conditions can have a severe impact, e.g., on the stability of rock walls. The energy balance model, PERMEBAL, was developed in order to simulate the changes and distribution of ground surface temperature (GST) in complex high-mountain topography. In such environments, the occurrence of permafrost depends greatly on the topography, and thus, the digital terrain model (DTM) is an important input of PERMEBAL. This study investigates the influence of the DTM on the modeling of the GST. For this purpose, PERMEBAL was run with six different DTMs. Five of the six DTMs are based on the same base data, but were generated using different interpolators. To ensure that only the topographic effect on the GST is calculated, the snow module was turned off and uniform conditions were assumed for the whole test area. The analyses showed that the majority of the deviations between the different model outputs related to a reference DTM had only small differences of up to 1 K, and only a few pixels deviated more than 1 K. However, we also observed that the use of different interpolators for the generation of a DTM can result in large deviations of the model output. These deviations were mainly found at topographically complex locations such as ridges and foot of slope

Influence of different digital terrain models (DTMs)on alpine permafrost modeling

The thawing of alpine permafrost due to changes in atmospheric conditions can have a severe impact, e.g., on the stability of rock walls. The energy balance model, PERMEBAL, was developed in order to simulate the changes and distribution of ground surface temperature (GST) in complex high-mountain topography. In such environments, the occurrence of permafrost depends greatly on the topography, and thus, the digital terrain model (DTM) is an important input of PERMEBAL. This study investigates the influence of the DTM on the modeling of the GST. For this purpose, PERMEBAL was run with six different DTMs. Five of the six DTMs are based on the same base data, but were generated using different interpolators. To ensure that only the topographic effect on the GST is calculated, the snow module was turned off and uniform conditions were assumed for the whole test area. The analyses showed that the majority of the deviations between the different model outputs related to a reference DTM had only small differences of up to 1 K, and only a few pixels deviated more than 1 K. However, we also observed that the use of different interpolators for the generation of a DTM can result in large deviations of the model output. These deviations were mainly found at topographically complex locations such as ridges and foot of slopes

Terrain modelling with triangle based free-form surfaces

Die Form der Geländeoberfläche spielt für viele GIS-Anwendungen einewichtige Rolle. Meistens wird in der Geländemodellierung aus den Inputdaten ein regelmässiges Gitter interpoliert. Dann wird auf das Gitter ein Algorithmus angewendet, welcher die gewünschte Geländeinformation extrahiert. Da solche Algorithmen verschiedene implizite Oberflächen verwenden kann so ein Vorgehen Inkonsistenzen zur Folge haben, falls für eine räumliche Modellierung mehrere Arten von Geländeinformation verwendet werden. Ausserdem wird so zweimal interpoliert, was auch nicht wünschenswert ist, da jeder Interpolationsschritt mit Unsicherheiten behaftet ist. Ein alternatives Vorgehen ist daher, eine kontinuierliche Oberfläche explizit zu spezifizieren und alle Geländeinformation direkt daraus abzuleiten.Die Rekonstruktion einer kontinuierlichen Oberfläche aus Punkt- und Liniendaten ist unterdefiniert. Es ist daher bei der Rekonstruktion wichtig, alle zur Verfügung stehende Information zu nutzen, damit die durch die Interpolation verursachten Unsicherheiten möglichst klein sind. Da man ein Interpolationsartefakt als ein Verhalten der Oberfläche anschauen kann, welches aufgrund des Vorwissens über Geomorphologie sehr unwahrscheinlich ist, schliesst dies das Vermeiden von Artefakten mit ein.Methoden aus dem Computer Aided Geometric Design (CAGD) scheinen für das Spezifizieren von kontinuierlichen Oberflächen sehr geeignet zu sein, da sie eine intuitive Beeinflussung der Oberflächenform erlauben. Diese Dissertion beschäftigt sich mit der Frage, inwiefern sich kubische Coons patches und Clough- Tocher Béziersplines für die digitale Geländemodellierung eignen. Das Grundprinzip von Coons patches besteht darin, aus einem Netzwerk von Randkurven eine geeignete Oberfläche zu finden, welche diese Kurven interpoliert. Clough-Tocher Béziersplines dagegen verwenden Kontrollpunkte, welche die Oberfläche anziehen und so deren Form beeinflussen. Im speziellen wird untersucht, wie lineare Information in diesen Oberflächen berücksichtigt werden kann sowie welche Artefakte auftreten und wie sie vermieden werden können. In der Geländemodellierung ist es oftmals wichtig, dass lineare Elemente auf der Oberfläche sind. Beispiele dafür sind Höhenlinien, Seekonturen oder Tallinien. Linien können in dreiecksbasierten Oberflächen berücksichtigt werden, indem gezwungene Delaunaytriangulationen verwendet werden. Bei einigen Linienelementen, z.~B. scharfen Graten, Seeufern oder Strassenrändern, kann es aber wünschenswert sein, dass die Oberfläche die Richtung aprupt ändert. Daher werden sowohl für die Coons patches als auch für die Clough-Tocher Bézier splines Erweiterungen entwickelt, welche die Berücksichtigung von Bruchkanten in den ansonsten kontinuierlich differenzierbaren Oberflächen ermölichen. In beiden Arten von Oberflächen gibt es eine Reihe von Artefakten, welche immer wieder auftreten. Die Verwendung von linear interpolierten Ableitungen senkrecht zu den Randkurven führt zu gut sichtbaren Artefakten. Um diese abzuschwächen wird eine Methode verwendet, um die Ueberg\änge zwischen zwei Bézierdreiecken möglichst glatt zu machen. Kubische Oberflächen können in langen und spitzen Dreiecken ausschwingen. Daher wird der Algorithmus von Ruppert verwendet, welcher durch Einfügen zusätzlicher Punkte kleine Winkel in der Triangulation verhindert.Die im Rahmen dieser Dissertation entwickelten Methoden werden mit Hilfe von künstlichen Oberflächen und mit Daten aus dem Feld evaluiert. Sowohl auf den künstlichen Oberflächen wie auch im Testgelände schneiden die kubischen Oberflächen verglichen mit der linearen Interpolation erheblich besser ab, weil sie auch die Krümmung des Geländes berücksichtigen. Auch die Berücksichtigung von Bruchkanten führt zu einer Verbesserung des Interpolationsergebnisses. Die Unterschiede zwischen den verschiedenen kubischen Interpolatoren sind bei allen Versuchen sehr klein. Zum einen sind die Unterschiede zwischen Coons patches und Clough-Tocher Bézier splines sehr klein, falls beide kubisch sind und dieselben Ableitungsfunktionen senkrecht zu den Randkurven haben. Zum anderen hat die Glättung der Clough-Tocher splines wohl einen Einfluss auf die visuelle Erscheinung der Oberflächen, die numerischen Effekte sind aber in allen Experimenten klein. The shape of the terrain surface is important for many GIS applications. Currently, digital terrain modelling is usually done by interpolation of theinput data to a regular grid and applying an algorithm to obtain therequired terrain derivatives. As several algorithms may use different implicitsurfaces, this approach may introduce inconsistency. Furthermore,interpolation is performed twice and because each interpolation step introducesuncertainty, this may not be optimal. An alternative approach is to specify acontinuous surface explicitly and to derive all terrain information from thissurface.Reconstruction of continuous surfaces from discrete input data isunderdefined. Therefore it is important to use all available information toreduce shape uncertainty. This includes the removal of artifacts because aninterpolation artifact can be seen as a surface behaviour which is, basedabout knowledge about terrain, implausible.Because of their intuitive shape control and their local nature, methods from Computer Aided Geometric Design (CAGD) seem to be well suited to continuous terrain modelling. This thesis examines the suitability of triangle-based Coons patches and Clough-TocherBézier splines for terrain modelling. The basic idea of Coons patches isto specify a network of boundary curves and to find a surface which passesthrough these curves. Clough-Tocher Bézier splines, in contrast, usecontrol points to describe the shape of the surface. Specifically, the possibilities toinclude linear information and the occurence and removal of artifacts withthese methods are examined. In terrain modelling it is often important that linear elementsare on the surface. Examples of such elements are contours, lake boundaries orvalleys. Linear elements can be considered in triangle-based surface by usingconstrained Delaunay triangulations. However, across some linear elements, forinstance sharp ridges, lake boundaries or road edges, it is desirable that thedigital surface changes its gradient aprupt. Therefore, extensions to include breaklines in otherwisecontinuously differentiable surfaces, are developed for Coons patches and Clough-Tocher splines. In both kinds of surfaces, different kinds of artifacts frequently occur. The usage of linear interpolated cross-derivatives, for instance, creates well visible artifacts. To soften these artifacts, a method to make the transitions between Clough-Tocher triangles smoother is introduced. Cubic surfaces may undulate in long and thin triangles. In this thesis, the Ruppert algorithm has been applied to alter the triangular meshsuch that small angles in long thin triangles disappear.The methods developed in the thesis are evaluated by means of artificial surfaces and field data. On the artificial surfaces as well as in the test area, the cubic free-form surfaces show a considerably improved prediction of elevations in comparison to linear interpolation because the cubic interpolators model the curvature of the terrain. The consideration of breaklines also improves the the predictions. The differences between the cubic interpolators are small in all experiments because of two reasons. First, although based on different mathematical formulations, Clough-Tocher Bézier splines and Coons patches don't show large differences if they have the same degree and the same cross-boundary derivative function. Second, the smoothing of the Clough-Tocher splines has an impact on the visual appearance of a surface, but the numerical effect of this extension is small in the experiments

Quantum GIS: il desktop GIS più potente, amichevole e libero

QuantumGIS is a free and open source GIS It has an intuitive graphical interface, suitable also for first time GIS users, and thanks to the integration with other free software (e.g. GRASS, PostGIS, GDAL) can read dozens of different formats, both raster and vector, link to OGC standard web services (WMS, WFS, SF) and run complex analysis and modeling. Many plugins make it easy to extend its functionality. It is used throughout the world, by thousands of users, and its development is fast, with new functions continuously added

Mathematisch-naturwissenschaftlichen Fakultät

zu

Open-Source GIS

The chapter explains the components of which an Open Source GIS is built of. They comprise the core software-component (mapserver), open source geospatial libraries, a typical open source GIS (Quantum GIS), the presently most widely spread open source database (PostgreSql) including its geospatial extension (PostGIS), and an overview over the most important license models. A mapserver can broadly be defined as a software platform for dynamically generating spatially referenced digital map products. The University of Minnesota MapServer or UMN MapServer, or simply MapServer, is one such system. Its basic features are visualization, overlay, and query. The mapserver architecture consists of a client, a server, and a database. The server is split up in three layers, the CGI-layer tying in to the network hardware, the geospatial analysis system, and the communication layer. Client and server do a load balancing for an optimal performance. The architecture is built upon the standards of the Open Geospatial Consortium of which those regarding interoperability are most important. The section concludes with a number of examples. The following section names and explains many of the geospatial open source libraries, starting with GDAL (raster) and OGR (vector). The other libraries are FDO (Feature Data Objects, JTS Topology Suite (JTS), GEOS, JCS Conflation Suite (JCS), MetaCRS, and GPSBabel. The application examples include derived GIS-software and data format conversions. The following section provides a detailed explanation of Quantum GIS, its origin and its applications. The features include a rich GUI, attribute tables, vector symbols, labeling, editing functions, projections, georeferencing, GPS support, analysis, and Web Map Server functionality. The architecture of Quantum GIS comprises a hierarchical set of several layers that ranges from data access via analysis to application. Future developments will address mobile applications, 3-D, and multithreading. The next section is dedicated to the database part. The origins of PostgreSQL are outlined and PostGIS discussed in detail. It extends PostgreSQL by implementing the Simple Feature standard. This allows applying a rich set of geospatial functions such as geometry types, e.g. polygons, relationships, e.g. within, and analysis function, e.g. convex hull. The last part of the chapter explains the most important open source licenses such as the GNU General Public License (GPL), the GNU Lesser General Public License (LGPL), the MIT license, and the BSD license, as well as the role of the Creative Commons

Correlation studies for B-spline modeled F2 Chapman parameters obtained from FORMOSAT-3/COSMIC data

The determination of ionospheric key quantities such as the maximum electron density of the F2 layer NmF2, the corresponding F2 peak height hmF2 and the F2 scale height HF2 are of high relevance in 4-D ionosphere modeling to provide information on the vertical structure of the electron density (Ne). The Ne distribution with respect to height can, for instance, be modeled by the commonly accepted F2 Chapman layer. An adequate and observation driven description of the vertical Ne variation can be obtained from electron density profiles (EDPs) derived by ionospheric radio occultation measurements between GPS and low Earth orbiter (LEO) satellites. For these purposes, the six FORMOSAT-3/COSMIC (F3/C) satellites provide an excellent opportunity to collect EDPs that cover most of the ionospheric region, in particular the F2 layer. For the contents of this paper, F3/C EDPs have been exploited to determine NmF2, hmF2 and HF2 within a regional modeling approach. As mathematical base functions, endpoint-interpolating polynomial B-splines are considered to model the key parameters with respect to longitude, latitude and time. The description of deterministic processes and the verification of this modeling approach have been published previously in Limberger et al. (2013), whereas this paper should be considered as an extension dealing with related correlation studies, a topic to which less attention has been paid in the literature. Relations between the B-spline series coefficients regarding specific key parameters as well as dependencies between the three F2 Chapman key parameters are in the main focus. Dependencies are interpreted from the post-derived correlation matrices as a result of (1) a simulated scenario without data gaps by taking dense, homogenously distributed profiles into account and (2) two real data scenarios on 1 July 2008 and 1 July 2012 including sparsely, inhomogeneously distributed F3/C EDPs. Moderate correlations between hmF2 and HF2 as well as inverse correlations between NmF2 and HF2 are reflected from the simulation. By means of the real data studies, it becomes obvious that the sparse measurement distribution leads to an increased weighting of the prior information and suppresses the parameter correlations which play an important role regarding the parameter estimability. The currently implemented stochastic model is in need of improvement and does not consider stochastic correlations which consequently cannot occur.Peer Reviewe

Diarrheagenic enteroaggregative Escherichia coli causing urinary tract infection and bacteremia leading to sepsis

We report a case of a 55-year-old immunocompromised female who presented to the emergency department with severe diarrhea and vomiting following travel to the Philippines. Stool bacteriology revealed a mixed infection involving an enteropathogenic Escherichia coli and two distinct strains of enteroaggregative Escherichia coli (EAEC). During hospitalization, urine and blood culture tested positive for one of the diarrheagenic EAEC strains, necessitating urinary catheterization, intensive care, and antimicrobial treatment with trimethoprim-sulfamethoxazole, followed by meropenem. Although known to occasionally cause urinary tract infections, EAEC have not been previously associated with sepsis. Our report highlights the potential of EAEC to cause severe extraintestinal infections

Towards an optimal overall description of electron density information gathered during GNSS satellite occultations

The purpose of this work is to characterize the performance of different interpolation methods in order to build a global model of ionospheric free electron density, directly derived from the inversions of GNSS occultation data. Indeed, the occultation of GNSS satellites, observed from dual-frequency L-band receivers onboard Low Earth Orbiters (LEOs) is providing valuable ionospheric data since the first mission (GPS/MET) in 1995. This is an excellent scenario to derive, in a simple and precise way, the almost instantaneous distribution of ionospheric electron density in a region of few thousands of kilometers from each occultation event. This can be done, for instance, applying the Improved Abel Transform Inversion technique proposed during the last decade by the UPC authors. In such approach the horizontal gradient of the electron density is taken from the Vertical Total Electron Content gradient as proxy. This assumption increases the accuracy of the electron density retrieval, compared with the Classical Abel Transform Inversion, which assumes spherical symmetry in the occultation region. The availability of numerous occultation events (up to 2000 per day during the full availability of the FORMOSAT-3/COSMIC LEO constellation) enables the execution of studies on the feasibility of simple but accurate ways to interpolate such fields of electron density values, given by each occultation, in an overall electron density modelPostprint (published version

Towards an optimal overall description of electron density information gathered during GNSS satellite occultations

The purpose of this work is to characterize the performance of different interpolation methods in order to build a global model of ionospheric free electron density, directly derived from the inversions of GNSS occultation data. Indeed, the occultation of GNSS satellites, observed from dual-frequency L-band receivers onboard Low Earth Orbiters (LEOs) is providing valuable ionospheric data since the first mission (GPS/MET) in 1995. This is an excellent scenario to derive, in a simple and precise way, the almost instantaneous distribution of ionospheric electron density in a region of few thousands of kilometers from each occultation event. This can be done, for instance, applying the Improved Abel Transform Inversion technique proposed during the last decade by the UPC authors. In such approach the horizontal gradient of the electron density is taken from the Vertical Total Electron Content gradient as proxy. This assumption increases the accuracy of the electron density retrieval, compared with the Classical Abel Transform Inversion, which assumes spherical symmetry in the occultation region. The availability of numerous occultation events (up to 2000 per day during the full availability of the FORMOSAT-3/COSMIC LEO constellation) enables the execution of studies on the feasibility of simple but accurate ways to interpolate such fields of electron density values, given by each occultation, in an overall electron density mode