Airborne LiDAR for DEM generation : some critical issues
This paper reviews the recent advances of airborne LiDAR systems and the use of LiDAR data for DEM generation, with special focus on LiDAR data filters, interpolation methods, DEM resolution, and LiDAR data reduction. Separating LiDAR points
into ground and non-ground is the most critical and difficult step for DEM generation from LiDAR data. Commonly used and most recently developed LiDAR filtering methods are presented. Interpolation methods and choices of suitable interpolator and DEM
resolution for LiDAR DEM generation are discussed in detail. Feature specific elements such as breaklines contribute significantly to DEM quality.
Emigration temporaire et économie dans le djebel Demmer (Tunisie présaharienne)
1976 ; Demmer, djebel ; Densité ; Djebalia, région ; Domination ; Démographie ; Economie régionale ; Emigration ; Exode rural ; Géographie de l'Afrique ; Importation ; Médenine, province ; Population ; Produit agricole ; Surnatalité ; Tunisie ; Vie
L'émigration fait vivre le Djebel Demmer. Une région tunisienne totalement dominée, une population entretenue sur un territoire au développement impuissant à rattraper le rythme démographique. (PmB).
The DEM of Mt. Etna : geomorphological and structural implications
A Digital Elevation Model (DEM) of Mt. Etna is presented. This 3-D view of Mt. Etna allowed both recognition and location of the main morphostructural and volcano-tectonic features of the volcano. A slope map has been generated from the DEM
Die Entwicklung der ländlichen kulturlandschaft zwischen dem Hochrhein und den Voralpen seit dem Spätmittelalter. (Evolution du paysage agraire entre le Rhin supérieur et les Préalpes depuis le bas Moyen Age)
Uber die Beziehung zwischen dem Widerstandkoeffizienten und dem Windweg über See bei ablandigem Wind in Küstennähe. (On the relation between the drag coefficient and fetch above the sea in the case of land wind in coastal areas)
Landnutzung und Entwicklungsmoglichkeiten in dem Trockengebieten Kenias Utilisation du sol et possibilités de développement dans les régions sèches du Kenya
Comparison of slope estimates from low resolution DEMs : scaling issues and a fractal method for their solution
Five different algorithms for calculating slope from digital elevation models (DEMs) have been compared from regional to global scales. The most significant outcome is that slope varies inversely with the DEM grid size. Thus, slopes estimated from
the high resolution slope based on the coarse resolution DEM by using fractal parameters.
Automatische extractie van topografische en geomorfologische variablen uit raster DEMs
Extraction automatique des variables topographiques et géomorphologiques avec la méthode de raster DEM
Different routines are described to calculate derived variables from raster DEMs such as slope, slope length, upstream drainage area, thalwegs, watersheds, waterdivides, concavities, convexities,...Also a description of new developed routines
is given, which allow additional information from raster DEMs. Examples in Greece, Spain, Belgium and Turkey are used to illustrate the use of the variables as descriptive geomorphological tools.
In this paper, some of the main flow accumulation algorithms and some existing techniques for dealing with closed depressions in DEMs are reviewed. A new algorithm is presented which assumes that such depressions are real features in the landscape
, and which allows them to ‘fill’ and then ‘overflow’ into downstream areas within the DEM. Examples with a synthetic and two real DEMs suggest that, at least in these cases, the assumption that depressions are real is justified. These results also suggest
that determining the size distribution for depressions within a DEM could form the basis for identifying whether artifact depressions are a problem in individual DEMs.
There is a growing interest in investigating the accuracy of digital elevation model (DEM). However people usually emphasize DEM sampling errors, but ignore the impact of DEM resolution and terrain roughness on the accuracy of terrain representation
. This research puts forward the concept of DEM terrain representation error (Et). A multi-resolution and multi-relief comparative approach is used as the major methodology in this research. The experiment reveals a quantitative relationship between the error
and the variation of resolution and terrain roughness at a global level. Root mean square error (RMS Et) is regressed against surface profile curvature (V) and DEM resolution (R) at 10 resolution levels.
DEM resolution effects on shallow landslide hazard and soil redistribution modelling
The AA. analyse the effects of digital elevation model (DEM) resolution on the results of a model that simulates spatially explicit relative shallow landslide hazard and soil redistribution patterns and quantities. They analyse distributions
of slope, specific catchment area and relative hazard for shallow landsliding for 4 different DEM resolutions (grid sizes of 10, 25, 50 and 100 m) of a 12 km2 study area in northern New Zealand. The effect of DEM resolution is especially pronounced
Terrestrial surface-area increment : the effects of topography, DEM resolution, and algorithm
To examine the effects of topography and data resolution on surface area calculation, the AA. calculated incremental area coefficients (IACs), based on 2 different algorithms, for a DEM of China at a series of spatial resolutions. Sampling the DEM
with a regional network of 50 km x 50 km cell size, they explored the relationships among the 2 IACs and topographic features. Between the IACs there was a linear relationship that varied with DEM resolution. For a specific type of geomorphology, a threshold
resolution of DEM can be determined, below which the surface-area increment (i.e., IAC) is negligible. The results provided the first comprehensive estimate of the contributions of the topographic features, DEM resolution, and algorithms for the surface-area
Drainage network extraction using LiDAR-derived DEM in volcanic plains
The commonly used methods for drainage network extraction from digital elevation models (DEMs) have limitations in low-relief terrain areas. Airborne light detection and ranging (LiDAR) offers high-accuracy terrain data. With LiDAR data, high
-accuracy and high-resolution DEMs can be generated. The results of drainage network extraction for 2 sub-catchments on the western Victorian Volcanic Plains (VVP) are reported. Drainage networks and some parameters describing drainage network composition
, including the stream orders, the numbers of streams and the stream lengths, were derived from both the LiDAR DEM and the Vicmap DEM. The LiDAR-derived DEM is shown to offer significantly more detail.
Evaluation of remotely-sensed DEMs and modification based on plausibility rules and initial sediment budgets of an artificially-created catchment
This study aimed to evaluate and to modify remotely-sensed DEMs for an improved quantification of initial sediment mass changes in an artificially-created catchment. DEMs were constructed from photogrammetry-based, airborne (ALS) and ground-based
laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three-dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region
-by-region for rill, interrill and alluvial areas, based on logical and hydro-geomorphological principles. Additional DEMs were constructed by combining multi-source, modified data. Models were evaluated by comparison with d-GPS reference data
and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics.
This paper aims to the evaluation of the assessment of topographic potential for erosion and deposition when the contour lines from the Czech Fundamental Base of Geographic Data (ZABAGED) are used. On a hill slope above the Opava River a DEM from
field measurements and a DEM from contours were created. The potential for erosion and deposition was computed on the both DEMs and the results were compared. - (EN)