Digital Elevation Models in high alpine terrain
Digital Elevation Models DEM are the basis for numerical simulations of gravitational mass movements (avalanches, debris flows and rockfalls) with RAMMS and for the assessment of terrain changes. Until today there are no high resolution DEM's (pixel size < 5m) for areas with an elevation of more than 2000m a.s.l. available in Switzerland. Therefore the major part of the investigation areas for alpine natural hazard research is not covered.
Up-to-date, high resolution digital elevation models can be acquired from the air using two different technologies:
- Airborne Laserscanning (ALS): Using LiDAR sensors based on airplanes or helicopters, the precise distance between the sensor and the earth surface can be measured. Measuring more than 150'000 points per second, these instruments can cover large areas within short time even in inaccessible terrain. This technology can acquire digital terrain models DTM, representing the earth surface without vegetation or buildings and digital surface models DSM, representing the top of the vegetation at the same time. But to cover large regions this method is very expensive.
- Photogrammetry: Using photogrammetric image correlation techniques, digital elevation models can be derived from airborne high resolution images. Because there are nearly no trees above 2000m a.s.l. in Switzerland it does not matter that this methodology is measuring a surface model not a terrain model. For large areas this method is much more economic and suitable sensors have a better availability. But the achieved vertical accuracy of the products is slightly worse than using LiDAR.
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How accurate are these elevation models?
The quantification of the achieved accuracies in X, Y and Z are essential for applications in science and practice. Within the test site Dorfbach in the Mattertal VS we compare the outputs of the different technologies with independently acquired differential global positioning system DGPS data. This research allows us to identify the advantages and disadvantages of the different technologies in high mountain terrain.