Raster Digital Elevation Models Research Articles

Identification and Visualization of Complex Spatial Pattern of Coastal Dune Soil Properties Using GIS-Based Terrain Analysis and Geostatistics

Coastal dunes display complex relationships among soil properties, vegetation, and geomorphology driven by marine and atmospheric dynamics. Considering topography as a fundamental control of the relations, this study investigated its influence on the spatial pattern of soil attributes in a coastal dune. We systematically collected 193 soil samples at intervals of 20 m from the Sindu coastal dunefield, South Korea, and analyzed 11 soil attributes. Principal component analysis extracted four main factors explaining ca. 75% of total soil variance. Correlation between each soil factor and topographic attributes calculated from raster digital elevation models permitted us to infer relationships between dune configuration and soil spatial variability. Interpretation of the first two factors demonstrated that nutrient input from marine sources by aeolian processes and topographic relief, an indirect measure of depth to the freshwater table, were two major determinants of the spatial distribution of soil properties. For the first factor, distance from the seashore proved to be the most significant indicator of edaphic conditions. Upslope area and wetness index were good proxies for the second factor, dune relief. These two variables significantly explained the distribution of soil moisture. A conceptual model is presented to describe how complex dune soil systems are created from simple topographic effects. The model addresses the importance of integrating foredune, dune slack, and inner dune ridge into one continuous system because topography, geomorphic (aeolian) processes, vegetation, and edaphic conditions are closely connected in a causal chain across the whole dune area.

Simulated and measured X‐band radar reflectivity of land in mountainous terrain using a fan‐beam antenna

A computer program for meteorological radar siting, previously developed for pencil‐beam antenna, long‐range, C‐band radars, has been adapted for fan‐beam antenna, short‐range, X‐band radars. The simulator uses topographic information in the form of a raster digital elevation model and a surface backscattering cross‐section per unit area at grazing angles derived from the literature. It is independent of specific radar sites and radar systems. Its use will enhance optimized scanning strategies, antenna design tailored to mountainous terrain and knowledge of land‐clutter measurements at low grazing angles. The raster‐based approach used in implementing the program makes it compatible with any desired spatial resolution. Simplicity and short simulation times have been pursued as primary goals during the planning and implementation phases of the routines. A preliminary validation of the simulator using backscattering data acquired in the Alps is presented in this letter.

Errors in river lengths derived from raster digital elevation models

Length of river reaches is one of the most important characteristics of stream networks when applying hydrological or environmental simulation models. A common method of obtaining estimates of river lengths is based on deriving flow directions, accumulated area and drainage lines from raster digital elevation models (DEM). This method leads to length estimates with variable accuracy, which depends on DEM horizontal resolution, flatness of terrain, DEM vertical accuracy, the algorithm used to obtain flow directions and the way by which distances are calculated over raster structures. We applied an automatic river length extraction method for eight river reaches in the River Uruguay Basin (206 000 km 2), in Southern Brazil, and compared its results to the lengths obtained from drainage vector lines digitalized over satellite images. Our results show that relative errors can be higher than 30% in flat regions with relatively low DEM resolution. Preprocessing of DEM by the method known as stream burning greatly improves results, reducing errors to the range 1.9–7.4%. Further improved estimates were obtained by applying optimized values for the length of orthogonal and diagonal steps called distance transforms, reducing the errors to the range −2.0–3.3%.

GIS-based modeling of secondary hydrocarbon migration pathways and its application in the northern Songliao Basin, northeast China

Hydrocarbon migration pathways are the linkage between hydrocarbon source areas and accumulation sites. Modeling accurately the pathways of hydrocarbon migration is of important significance in determining the location of favorable petroleum exploration targets. In this paper, GIS-based modeling algorithms are presented for searching the pathways of secondary hydrocarbon migration by considering the geologic mechanisms. These algorithms are constructed on a raster digital elevation model (DEM) of the top boundary of a carrier bed, in which secondary migration occurred. On the DEM, a 3×3 pixel sized window is used for searching. The center of the search window is initially assumed at a point on the boundary of a hydrocarbon source area, from which the secondary hydrocarbon migration starts. The altitude values in the eight adjoining pixels enclosing the central pixel of the search window are compared, and the pixel with an altitude value not only larger than the central pixel but also the largest of the eight surrounding pixels is the next target pixel where the search window will move to. Each searched path will terminate at either a convex point, which indicates the existence of a trap for hydrocarbon accumulation, or a point on the boundary of the DEM, which suggests that the pathway of hydrocarbon migration extends outside the DEM. In addition, a concourse point of two paths is also considered as a termination point of either path. The algorithms were successfully applied in the modeling of the secondary migration pathways in the northern Songliao Basin, northeast China. The modeled results matched well with drilling data, suggesting the robustness of the algorithms.

Derivation of Geodesic Flow Fields and Spectrum in Digital Topographic Basins

We present a framework to characterize terrestrial functions—surficial and bottom topographic regions that are represented, respectively, as raster digital elevation models (DEMs) and digital bathymetric models (DBMs)—through analysis of flow fields that are simulated via geodesic morphology. Characterization of such functions is done via a new descriptor. Computation of this new descriptor involves the following steps: (i) basin in digital form representing topographic fluctuations as an input, (ii) threshold decomposition of basin—that consists of channelized and nonchannelized regions—into sets, (iii) proper indexing of these sets to decide the marker set(s) and its (their) corresponding mask set(s), (iv) performing geodesic propagation that provides basic flow field structures, and (v) finally providing a new basin descriptor—geodesic spectrum. We demonstrated this five-step framework on five different synthetic and/or realistic DEMs and/or DBMs. This study provides potentially invaluable insights to further study the travel-time flood propagation within basins of both fluvial and tidal systems.

Modelling the urban climate using a local governmental geo‐database

AbstractIn this study, local government digital spatial data are used to describe urban geometry and analyse spatial variations of the urban climate within the central areas of Göteborg, Sweden. A high‐resolution raster digital elevation model (1 m pixel resolution) consisting of building structures and ground heights is derived from a local government geo‐database, as well as land use patterns and artificial heat sources. Parameters such as the sky view factor (SVF) and daily averages of solar radiation are calculated. Results obtained from the model are compared with intra‐urban air temperature variations which are derived from mobile measurements, as well as surface temperature variations derived from thermal infrared images. Results show that high‐resolution digital elevation models in raster format are very useful sources of data for the investigation of intra‐urban temperature variations. Results also show that the areal mean of SVF correlates with intra‐urban air temperature variations to a higher degree than SVF that is taken from a point source location. The correlation between the modelled SVF and surface temperature is high during both spring and winter. Adding information about daily averages of global radiation for the spring measurement causes the correlation between SVF and surface temperature variations to increase. Copyright © 2007 Royal Meteorological Society

A methodology for aligning raster flow direction data with photogrammetrically mapped hydrology

The requirement to digitally delineate accurate watershed boundaries is a routine task necessary in numerous natural science disciplines. The base topographic data necessary for watershed analysis in many jurisdictions is typically contained within two primary photogrammetrically interpreted base topographic layers: the hydrology (streams, rivers, wetlands, lakes, etc.), and the elevation (contours, spots, digital terrain model points, etc.). From these two data sources, a flow direction corrected, single line, vector hydrology network and a raster digital elevation model can be developed. There are numerous approaches to watershed delineation, but the most accurate implementations employ both these enhanced data sets in extracting watershed divides. A popular method to increase the accuracy of extracted watershed boundaries is to utilize that hydrology network to post-condition the digital elevation model, thus ensuring the local topography honours the stream network. This process is known as stream burning. This paper outlines an alternative approach to accomplish a similar objective. The outlined approach unambiguously translates the topological relationships within the vector hydrology layers directly into a raster flow direction grid. Initial testing of this methodology has shown several accuracy and processing advantages for extracting watershed boundaries.

Study on the estimation of precipitation resources for rainwater harvesting agriculture in semi-arid land of China

Rainwater harvesting agriculture (RHA) can be a valuable practice in increasing crop productivity in the semi-arid region of Loess Plateau in China. Due to lack of the detailed data of precipitation resources in the region, there have been some difficulties in the development of rainwater harvesting agriculture. In this research, based on the precipitation data in the last 40 years and topographical maps at 25 observation stations in and around Dingxi County, Gansu Province, China, the raster digital elevation models (DEM) and the average annual precipitation (AAP) databases in the study areas were established using ARC/INFO geographical information system (GIS) technology. By means of interpolation approaches, statistical model and comprehensive approach including nine methods (inverse distance weighted (IDW), trend (TRE), spline (SPL), ordinary Kriging (OKR), universal Kriging 1 (UK1), universal Kriging 2 (UK2), Thissen polygon (THP), multivariate regression (MVR) and comprehensive approach (COM)), the spatial and temporal changes of AAP were calculated and comparatively analyzed. Results indicate that simulating precision of the comprehensive method is the best in the nine approaches, and its maximum relative error is 6.40% and the range of error is 11.66%. The next is ordinary Kriging method with exponential model to simulate semivariogram, and its maximum relative error reaches 6.76%. As far as the seven kinds of interpolation approaches are concerned, the precision of ordinary Kriging method is the best, and the error of statistical model is relatively high, of which the maximum relative error reaches 9.04%. The AAP in Dingxi County calculated by comprehensive approach is 420 mm, and the water deficit of spring wheat is about 226 mm, so rainwater harvesting agriculture is feasible in the study area if reasonable harvesting technologies are taken. The AAP information system, established by raster precipitation spatial databases using optimized methods, can quickly and timely calculate the total quantities and the spatial changes of precipitation resources on any scales in the study areas, which has an important role in runoff simulating, engineering planning, strategy developing, and decision making as well as water management in rainwater harvesting agriculture.

Drainage density, slope angle, and relative basin position in Japanese bare lands from high-resolution DEMs

Relationships between drainage density and slope angle for three bare lands in Japan were analyzed with special attention to channels at early erosion stages and channels in a badland-type terrain. Two of the bare lands were caused by volcanic eruptions 1 or 30–40 years ago, and the other one is a landslide scar formed more than 100 years ago. Raster digital elevation models (DEMs) with a 1-m resolution and ortho aerial photos were generated using digital photogrammetry to enable detailed stream-net extraction and topographic analyses. Data for drainage density, slope angle, and relative height for 88 subwatersheds were obtained from the DEMs and derived stream-nets. The relationship between drainage density and slope angle for each subwatershed can be divided into two types: downward sloping and convex upward. Although previous studies suggested that drainage density positively correlates with slope angle if overland flow is dominant, this correlation seldom occurs in the study areas. The two types of drainage density–slope angle relationships correspond to differing channelization stages that reflect the extension and integration of existing channels, as well as the formation of new low-order streams in response to base-level lowering. The location of subwatersheds within each study area seems to play a major role in determining the stages of channel development and, in turn, the types of drainage density–slope angle relationships.

The Effect of DEM Raster Resolution on First Order, Second Order and Compound Terrain Derivatives

AbstractIt is well known that the grid cell size of a raster digital elevation model has significant effects on derived terrain variables such as slope, aspect, plan and profile curvature or the wetness index. In this paper the quality of DEMs derived from the interpolation of photogrammetrically derived elevation points in Alberta, Canada, is tested. DEMs with grid cell sizes ranging from 100 to 5 m were interpolated from 100 m regularly spaced elevation points and numerous surface‐specific point elevations using the ANUDEM interpolation method. In order to identify the grid resolution that matches the information content of the source data, three approaches were applied: density analysis of point elevations, an analysis of cumulative frequency distributions using the Kolmogorov‐Smirnov test and the root mean square slope measure. Results reveal that the optimum grid cell size is between 5 and 20 m, depending on terrain com‐plexity and terrain derivative. Terrain variables based on 100 m regularly sampled elevation points are compared to an independent high‐resolution DEM used as a benchmark. Subsequent correlation analysis reveals that only elevation and local slope have a strong positive relationship while all other terrain derivatives are not represented realistically when derived from a coarse DEM. Calculations of root mean square errors and relative root mean square errors further quantify the quality of terrain derivatives.

Development and application of a new algorithm for automated pit removal for grid DEMs

Pits and flat surfaces in raster digital elevation models (DEMs) have been unavoidable obstacles in the extraction of drainage networks. A new automatic method of “pits filling” is presented that eliminates all pits and flat areas simultaneously. Spatially distributed elevation increments of pits are computed. Based on this new approach, drainage networks of more than 10 medium- to large-sized basins have been extracted, including the Mekong River and the Yangtze River. Overlaying the computed drainage networks onto the digitized actual stream networks, good visual consistency was obtained. Besides, the calculated flow pattern over a flat area has been shown to be convergent. The results indicate that the proposed algorithm is easy to use and applicable to DEMs with a wide range of terrain relief and resolution.

The Methods and Application of Automatically Extracting Stream Network of Watershed

讨论由栅格数字高程模型(DEM)自动提取流域水系的原理和方法,并以西苕溪中上游流域为研究区进行了河网生成实验. 研究表明:在山地丘陵区和平均地形坡度不小于3°的区域,所生成河网具有很高的可靠性. 为了解决在平均地形坡度小于3°的平坦区域河网生成中产生的虚拟河网与自然水系偏差较大的问题,提出了利用主干河道和平原水系数字化作为约束条件的生成河网的方法,取得了与实际情况比较接近的结果,从而使水文要素的模拟更具有实际意义.;At present, with digital terrain analysis technologies, calculating topographic information directly, modeling hydrological process and extracting hydrological data automatically from digital elevation models (DEM) is the focus of digital hydrology, and the present Geographic Information System (GIS) software based on raster data structure provide solid foundation for the modeling hydrological process, too. Automated extraction of drainage features from DEM is a very important research item of them, and has been widely used in actual works. The paper discussed the principles, methods and process of automated extraction of natural stream networks of watershed from DEM. The upper reaches watershed of Xitiaoxi as a case of study, a raster DEM is used to define surface drainage and extract the stream networks. Through comparing the stream networks delineated from DEM with the actual stream networks, it can be conclude that in the mountains area, especially the area of mean slope no less than 3 degrees, the delineated stream networks would be reliable. In the flat region of mean slope less than 3 degrees, the delineated stream is much different from the actual stream networks. In order to solve the problem, we put forward the restricted river channel method by digitizing the trunk streams and the flat land rivers. With the method, we got the delineated steam networks same as the actual stream networks, and make the simulation of hydrologic factor has more practical value. The method has universal reference value for hydrological modeling of other watersheds, and can improve the efficiency of hydrological modeling obviously.

A Computational Environment for Water Flow along Floodplains

A numerical model for the computer simulation of large floodplain inundations is presented. The model is extremely simple in order to achieve efficient computations in regions greater than 1000 km 2 . It is based on raster Digital Elevation Models (DEMs) and rules for water interchange between neighbor cells. The computer implementation, AQUA code, includes facilities for interpolation of precipitation data, graphics visualization and interactive DEM modification for simulation of alternative scenarios. The numerical performance was analyzed in some simple cases and the model was applied to a 1600 km 2 landscape corresponding to the region of Pehuajo in Argentina, which experiences frequent floodings.

DEM Manipulation and 3-D Terrain Visualization: Techniques Used by the U.S. National Park Service

Manipulating digital elevation model (DEM) surfaces, like pliable modelling clay, enhances the appearance and legibility of 3-D topography on maps. The U.S. National Park Service (NPS) uses the familiar image-editing tools in Adobe Photoshop to manipulate raster DEM data. Exporting modified DEM data with the help of freeware and shareware utilities allows subsequent rendering of final 3-D scenes in Corel Bryce. Techniques to be discussed include topographic substitution – a method for reverse engineering present-day landscapes into the past or projecting them into the future; selective vertical exaggeration; resolution bumping – a technique developed specifically for improving the legibility of high-mountain landscapes; painting and filtering effects; and, borrowing from the traditional masters of landform depiction, creating 3-D scenes that emulate the panoramas of Heinrich Berann and the spherical over-the-horizon views of Richard Edes Harrison by warping the projection plane of DEMS. The unique challenges of 3-D mountain mapping and the continuing pursuit of design excellence – a cornerstone of the NPS cartographic program – are overarching themes.

GIS‐based rapid assessment of erosion risk in a small catchment in the wet/dry tropics of Australia

AbstractAssessing the impact of various land uses on catchment erosion processes commonly requires in‐depth research, monitoring and field data collection, as well as the implementation of sophisticated modelling techniques. This paper describes the evaluation of a geographic information system (GIS)‐based rapid erosion assessment method, which allows the user to quickly acquire and evaluate existing data to assist in the planning of more detailed monitoring and modelling programmes. The rapid erosion assessment method is based on a simplified version of the revised universal soil loss equation (RUSLE), and allows the rapid parameterization of the model from widely available land unit and elevation datasets. The rapid erosion assessment method is evaluated through the investigation of the effects of elevation data resolution on erosion predictions and field data validation. The use of raster digital elevation model (DEM)‐derived data, as opposed to vector land unit relief data, was found to greatly improve the validity of the rapid erosion assessment method. Field validation of the approach, involving the comparison of predicted soil loss ratios with adjusted in‐stream sediment yields on a subcatchment basis, indicated that with decreasing data resolution, the results are increasingly overestimated for larger catchments and underestimated for smaller catchments. However, the rapid erosion assessment method proved to be a valuable tool that is highly useful as an initial step in the planning of more detailed erosion assessments. Copyright © 2001 Commonwealth of Australia.

Identification of the spatial distribution of soils using a process-based terrain characterization

A simple process-based terrain characterization model was developed to identify the occurrence of soils over a complex landscape. Its basic proposition is that soil distribution can be most efficiently identified by the separation of pedogeomorphological units where similar hydrological, geomorphological, and pedological processes occur. The proposed model is a three-dimensional extension of the nine-unit soil landscape model. The two-dimensional conceptual and qualitative model is reinterpreted in terms of continuity equations describing the distribution of soil materials over hillslopes, and is implemented in a geographical information system (GIS) through the analysis of a raster digital elevation model (DEM). The application of this model at the Empire Prairie in southern Wisconsin, USA, shows a good agreement with the results of a soil investigation. The difficulty in modeling the diverse geomorphological and pedological processes at low lying slope positions and the influence of relict pedological features on contemporary soil formation, however, remain unsolved. This model can consider the spatial variability of soils both at the continuous and discrete scales, and is easily transferable to other slopes in a predictive manner. It is further expected to provide a quantitative tool to characterize surface topography in terms of process identification and resource survey, and also a priori information for spatially distributed ecological and environmental models.

Determination of the drainage structure of a watershed using a digital elevation model and a digital river and lake network

Distributed hydrological models require a detailed definition of a watershed's internal drainage structure. The conventional approach to obtain this drainage structure is to use an eight flow direction matrix (D8) which is derived from a raster digital elevation model (DEM). However, this approach leads to a rather coarse drainage structure when monitoring or gauging stations need to be accurately located within a watershed. This is largely due to limitations of the D8 approach and the lack of information over flat areas and pits. The D8 approach alone is also unable to differentiate lakes from plain areas. To avoid these problems a new approach, using a digital river and lake network (DRLN) as input in addition to the DEM, has been developed. This new approach allows for an accurate fit between the DRLN and the modelled drainage structure, which is represented by a flow direction matrix and a modelled watercourse network. More importantly, the identification of lakes within the modelled network is now possible. The proposed approach, which is largely rooted in the D8 approach, uses the DRLN to correct modelled flow directions and network calculations. For DEM cells overlapped by the DRLN, flow directions are determined using DRLN connections only. The flow directions of the other DEM cells are evaluated with the D8 approach which uses a DEM that has been modified as a function of distance to the DRLN. The proposed approach has been tested on the Chaudière River watershed in southern Québec, Canada. The modelled watershed drainage structure showed a high level of coherence with the DRLN. A comparison between the results obtained with the D8 approach and those obtained by the proposed approach clearly demonstrated an improvement over the conventionally modelled drainage structure. The proposed approach will benefit hydrological models which require data such as a flow direction matrix, a river and lake network and sub-watersheds for drainage structure information.

A simple raster-based model for flood inundation simulation

In this paper the development of a new model for simulating flood inundation is outlined. The model is designed to operate with high-resolution raster Digital Elevation Models, which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation. This consists of a one-dimensional kinematic wave approximation for channel flow solved using an explicit finite difference scheme and a two-dimensional diffusion wave representation of floodplain flow. The model is applied to a 35 km reach of the River Meuse in The Netherlands using only published data sources and used to simulate a large flood event that occurred in January 1995. This event was chosen as air photo and Synthetic Aperture Radar (SAR) data for flood inundation extent are available to enable rigorous validation of the developed model. 100, 50 and 25 m resolution models were constructed and compared to two other inundation prediction techniques: a planar approximation to the free surface and a relatively coarse resolution two-dimensional finite element scheme. The model developed in this paper outperforms both the simpler and more complex process representations, with the best fit simulation correctly predicting 81.9% of inundated and non-inundated areas. This compares with 69.5% for the best fit planar surface and 63.8% for the best fit finite element code. However, when applied solely to the 7 km of river below the upstream gauging station at Borgharen the planar model performs almost as well (83.7% correct) as the raster model (85.5% correct). This is due to the proximity of the gauge, which acts as a control point for construction of the planar surface and the fact that here low-lying areas of the floodplain are hydraulically connected to the channel. Importantly though it is impossible to generalise such application rules and thus we cannot specify a priori where the planar approximation will work. Simulations also indicate that, for this event at least, dynamic effects are relatively unimportant for prediction of peak inundation. Lastly, consideration of errors in typically available gauging station and inundation extent data shows the raster-based model to be close to the current prediction limit for this class of problem.

Estimating Flow Distribution over Digital Elevation Models Using a Form-Based Algorithm

This paper discusses a new approach to estimate flow distribution over a continuous surface. This approach is based on the analysis of topographic form of a surface facet that dictates the flow distribution. In the case of a raster Digital Elevation Model (DEM), the facet consists of a centre cell and its eight neighbouring cells. If the form of the facet is convex, the water flow is divergent; thus the amount of flow is distributed to all cells that have a lower elevation. In the case of a concave or flat surface, the convergent flow is directed to the main drainage direction. Comparison between the results of this algorithm with the traditional ‘eight-move’ algorithm, which is widely used in today's commercial GIS software, indicated that the form-based algorithm yielded a more realistic results in estimating flow accumulation over the land surface, but produced less convincing results in deriving a drainage network.

Simulation of the Orographic Influence on Weather Radar Using a Geometric–Optics Approach

Abstract A computer code for radar site assessment, including ground clutter, beam occultation, and earth curvature–atmospheric refraction factors, has been developed. The code uses topographic information in the form of a raster Digital Elevation Model, air refractive index profile in the boundary layer, surface backscattering cross section per unit area at grazing angles as derived from literature, and ancillary information, if available, derived from a land use–land cover map. This algorithm is independent of a specific radar site and radar system. Several benefits in dealing with open problems of radar meteorology and of radar design could be derived from its use, namely, better estimate of precipitation at ground level through vertical echo profile correction, scanning strategy, land clutter measurements at low grazing angles, and characterization of seasonal and topographic effects. The raster-based approach used in implementing the code makes it compatible with any spatial resolution desired. Simpl...