Digital Elevation Model

Urban flooding is an inevitable problem for many cities around the world. In the present paper, modelling approaches and principles for analyses of urban flooding are outlined. The paper shows how urban flooding can be simulated by one-dimensional hydrodynamic ...

GIS (Geographical Information System) is one of the most striking innovation for mapping applications supplied by the developing computer and software technology to users. GIS is a very effective tool which can show visually combination of the geographical and non-geographical data by recording these to allow interpretations and analysis. DEM (Digital Elevation Model) is an inalienable component of the GIS. The existing TM (Topographic Map) can be used as the main data source for generating DEM by amanual digitizing or vectorization process for the contours polylines. The aim of this study is to examine the DEM accuracies, which were obtained by TMs, as depending on the number of sampling points and grid size. For these purposes, the contours of the several 1/1000 scaled scanned topographical maps were vectorized. The different DEMs of relevant area have been created by using several datasets with different numbers of sampling points. We focused on the DEM creation from contour line...

Watershed management and early warning flood forecasting system is becoming more and more important especially in relation to anticipated climate change. The characteristics and the validation of the Cetemps HYdrological Model (CHYM) developed by the hydrological group of the Cetemps Center of Excellence are described. CHYM is a grid based model and the main physical processes concerning the hydrological cycle are implemented in the model (Todini and Ciarrapica, 2002; Sorooshian et al., 1995). In the preprocessing phase different data sources are assimilated by the model in order to reconstruct precipitation field on the area of interest. At the moment the available data are the observed rain gauge values, the forecasted MM5 precipitation fields and the satellite rainfall estimation (Grimes et al., 2003). This multisources data acquisition system using observed and forecasted data makes it possible to simulate a time window that span from few days before the event to few days after....

Recently, due to the excessive raining, some land and houses have been seen under water and faced with flood disaster. In order to prevent this catastrophe, taking measures beforehand is so important. For this reason, in order to help with planning while land arrangements in urban and ru- ral areas are done, hydrologically analyzing the DEMs produced from the satellite

Flood related scientific and community-based data are rarely systematically collected and analysed in the Philippines. Over the last decades the Pagsangaan River Basin, Leyte, has experienced several flood events. However, documentation describing flood characteristics such as extent, duration or height of these floods are close to non-existing. To address this issue, computerized flood modelling was used to reproduce past events where there was data available for at least partial calibration and validation. The model was also used to provide scenario-based predictions based on A1B climate change assumptions for the area. The most important input for flood modelling is a Digital Elevation Model (DEM) of the river basin. No accurate topographic maps or Light Detection And Ranging (LIDAR)-generated data are available for the Pagsangaan River. Therefore, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Map (GDEM), Version 1, was chosen...

Catastrophic flank collapses have occurred at many stratovolcanoes worldwide. We present a three-dimensional (3-D) slope stability analysis for assessing and quantifying both the locations of minimum edifice stability and the expected volumes of potential failure. Our approach can search the materials underlying a topographic surface, represented as a digital elevation model (DEM), and determine the relative stability of all parts of the edifice. Our 3-D extension of Bishop's [1955] simplified limit-equilibrium analysis incorporates spherical failure surfaces, variable material properties, pore fluid pressures, and earthquake shaking. Although a variety of processes can trigger collapse, we focus here on gravitationally induced instability. Even homogeneous rock properties strongly influence the depth and volume of the least stable potential failure. For large failures in complex topography, patterns of potential instability do not mimic local ground surface slope alone. The May 18, 1980, catastrophic failure of the north flank of Mount St. Helens provides the best documented case history to test our method. Using the undeformed edifice topography of Mount St. Helens in an analysis of dry, static slope stability with homogeneous materials, as might be conducted in a precollapse hazard analysis, our method identified the northwest flank as the least stable region, although the north flank stability was within 5% of the minimum. Using estimates of the conditions that existed 2 days prior to collapse, including deformed topography with a north flank bulge and combined pore pressure and earthquake shaking effects, we obtained good estimates of the actual failure location and volume. Our method can provide estimates of initial failure volume and location to aid in assessing downslope or downstream hazards.

Gridding methods produce a regularly spaced, rectangular array of Z values from irregularly spaced XYZ data. Gridding generates a Z value at each grid node by interpolating or extrapolating the data values. Different gridding methods provide different interpretations of data because each method calculates grid node values by using a different algorithm. In this paper, we apply and compare different gridding methods including Inverse Distance Weighting, Kriging, Minimum Curvature, Modified Shepard's Method, Natural Neighbor, Nearest Neighbor, Polynomial Regression, Radial Basis Function, Triangulation with Linear Interpolation, Moving Average and Local Polynomial for various pilot regions with varied elevations. Grid method parameters which are able to set when producing a grid file, control the interpolation procedures. We also change these parameters to evaluate their effects on the resulted precision. We use a set of checkpoints to compare the precision of these methods. To implement these methods, various elevation data with equal precision is used; therefore, the results are affected only by the interpolation method. In other words, the influences of data and other environmental factors on the resulted precision are reduced by using them similarly in all gridding methods. Eventually, RMSE is computed for each method with its special parameters in different regions using checkpoints. The resulted precision acquired from applying these methods as well as their advantages and disadvantages in various topographic regions are represented in this study.

Experiments of the two-pass interferometric Synthetic Aperture Radar (IfSAR) technique shows that the method often gives poor result due to poor coherence and to different physical conditions. For this reason, the stereoscopic Synthetic Aperture Radar (SAR) method presents an important alternative for terrain mapping. To automate the image matching procedures and to reduce the requirement of GCPs is a major consideration in the generation of Digital Elevation Models (DEMs) from space-borne SAR data. This paper describes a pyramidal image matching scheme with an optimized parameter selection strategy and a region-growing technique to achieve a high level of automation for producing Digital Parallax Models (DPMs) from same-side image pairs. A DPM provides successful matched points of an image pair. The strategy is mainly based on the analysis of the maximal parallax in an image pair and a pyramidal geometry. A rigorous algorithm for space intersection is used to generate DEMs from DPM...

We developed the model PHENIPS for spatial and temporal simulation of the seasonal development of Ips typographus at the Kalkalpen National Park in Austria. The model is based on a digital elevation model used for interpolation of temperature and solar radiation to calculate the microclimatic conditions (bark temperature) for the beetles’ development. Additionally, the beetles’ phenology at Kalkalpen National Park was monitored along with air and bark temperature measurements. The onset of host tree infestation in spring was estimated using a lower threshold of 16.5 °C for flight activity and a mean thermal sum of 140 degree-days (dd) from beginning of April 1st onward. Rate of brood development was calculated from accumulated degree-days of hourly temperature data using upper and lower temperature thresholds of 38.9 and 8.3 °C, respectively, and a nonlinear function for calculating effective thermal sums. Re-emergence of parental beetles occurred at a time when 49.7% of the thermal sum for total development (557 dd) was reached. The model includes the discontinuance of the beetle's reproductive activity at a day length <14.5 h. The rate of successful hibernation of established broods is predicted by assessing the developmental stage of initiated generations at the beginning of the cold period. For validation we compared the timing of phenological events in the field with predicted events using both, hourly recorded data at trap trees in the terrain and generated daily topoclimatic data. Using topoclimatic data, the onset of infestation was predicted with a mean absolute error of 1.3 days. The observed onset of emergence of filial beetles in the field was estimated with a mean error of 39 dd. Our PHENIPS explicitly considers the strong effects of regional topography and stand conditions on local air and bark temperature and can be used for precise monitoring of the actual state of bark beetle development at the specific stand/tree level. Using topoclimatic data, PHENIPS simulates the maximum number of generations which is necessary to assess the potential impact of bark beetle outbreaks at regional scale. Further applications of PHENIPS for site-specific hazard rating of bark beetle infestation are discussed.

Physically based models are commonly used as an integral step in landslide hazard assessment. Geomorphic principles can be applied to a broad area, resulting in first order assessment of landslide susceptibility. New techniques are now available that may result in the increased accuracy of such models. We investigate the possibility to enhance landslide susceptibility modeling by integrating two physically-based landslide models, the Factor of Safety (FS) and the Shallow Stability model (SHALSTAB), with traditional empirical-statistical methods that utilize terrain attribute information derived from a digital elevation model and land use characteristics related to forest harvesting. The model performance is measured by the area under the receiver operating characteristic curve (AUROC) and sensitivity at 90% and 80% specificity both estimated by bootstrap resampling. Our study examines 278 landslide initiation points in the Klanawa Watershed located on Vancouver Island, British Columbia, Canada. We use a generalized additive model (GAM)and a logistic regression model (GLM) combining physical landslide models, terrain attributes and land use data, and GAMs and GLMs using only subsets of these variables.In this study, all empirical and combined physical-empirical models outperformthe physically-based models, with GAMs often performing significantly better than GLMs. The strongest predictive performance is achieved by the GAMsusing terrain attributes in combination with land use data. Variables representing physically-based models do not significantly improve the empirical models, but they may allow for a better physical interpretation of empirical models. Also, based on bootstrap variable-selection frequencies,land use data, FS, slope and plan/profile curvature are relatively the most important predictor variables.

In this study, an effort was made to simulate the transformation of rainfall into runoff, in a small experimental mountainous-forested watershed in western Greece. The main objective was the production of flood hydrographs by calculating average flow velocities (inside and outside the stream network). The usefulness of the flow velocities lies in using them in other ungauged small-forested watersheds that have similar geomorphological and hydrological characteristics. The meteorological and hydrological data of four storm events were obtained from the corresponding stations that are located near and at the outlet of the watershed, respectively. Geographic Information Systems (GIS) technology was used for the obtainment of the spatially distributed watershed characteristics. The resolution of the digital elevation model and the produced rasters was 50X50 m2. By integrating all information, a simplified model was developed, which is based on the Time – Area (TA) rainfall – runoff flow...

Fold geometry versus axis orientation can be used to constrain the kinematics of transpressional plate boundaries. This approach is typically based on bedding orientation data collected in the field, however, in some regions outcrop quality is insufficient to provide enough measurements. We extract orientation data from a georeferenced geologic map and a digital elevation model and to constrain the kinematics of a poorly exposed, active transpressional boundary: the Central Range Fault zone in Trinidad. Strike-and-dip orientations are calculated based on contact positions extracted from the digital geologic and topographic datasets. The uncertainties in the both horizontal position and elevation of the contact are propagated into the final kinematic analysis. Analysis of folds adjacent to the Central Range Fault suggests the angle of oblique convergence in transpression (α) varies from 20° to 85°. The majority of folds, however, are consistent with a large component of contraction (...