Digital Elevation Models (DEMs) are an integral part of any geospatial analysis. They are required both for the description of the three dimensional surface and to orthorectify the imagery. Both of which can be used as a backdrop and to provide derived information for modelling purposes.
The term DEM is a generic term that includes two distinct topographic models and it is important to recognise the distinction as it will affect how useful the model is for any application.
A Digital Elevation Model (DEM) is a digital model or 3D representation of a terrain’s surface – created from terrain elevation data.
A Digital Surface Model (DSM) represents the earth’s surface and includes all objects on it. This will include the heights of cultural features such as buildings, road and vegetation as well as bare earth.
A Digital Terrain Model (DTM) represents the bare ground surface in which all the cultural features such as buildings and trees have been removed.
While a DSM may be useful for landscape modelling, city modelling and visualisation applications, a DTM is often required for flood or drainage modelling, land-use studies, geological purposes and other applications.
DEMs can be created from stereo imagery provided by a wide range of sensors. The scale and level of detail required in an individual project will determine the spatial resolution and accuracy of the DEM required.
DEMs are available in various resolutions to suit differing application and budgets, for example a 50cm DEM may be required for detailed hydrological modelling whilst a 1m DEM might be more cost effective and suitable for environmental planning. A 5m DEM may be the most budget friendly solution for large area topographic mapping for exploration or initial greenfields feasibility studies.
Benefits of using satellite imagery to create DEMs
- Worldwide availability of satellite data without any access restrictions
- Large area coverage
- Resolution from very high to regional
- Fast processing time
- Low processing cost
Common uses of DEMs include:
- Extracting terrain parameters
- Modelling water flow or mass movement (e.g. avalanches and landslides)
- Creation of relief maps
- Orthorectification of aerial photography of satellite imagery
- Terrain analysis in geomorphology and physical geography
- Engineering and infrastructure design
- Line-of-sight analysis
- Base mapping
- Hydrological modelling – flood mitigation or watershed analysis
- Environmental change application
- Risk assessment.