Environmental observation requires not only high-resolution spatial and temporal data, but also data on the third dimension. We have developed a method that enables precise observation of small changes in the landscape over a relatively short period of time and in all three dimensions.
Monitoring programmes such as landscape monitoring require appropriate methods to record land and soil usage and analyse their development. We apply and enhance existing methods. In this way, we are improving the environmental monitoring data bases. Consequently, it is now possible to analyse the landscape in three dimensions. Thus, not only can we record the type of land use, for example the extent of the forest surface area, but also the surface area and height of the trees. This has been made possible with the aid of "Airborne Laser Scanning (ALS)" which measures the distances to the surface from an aeroplane. With high vegetation such as trees, the laser beams partially penetrate through the actual surface and reach the underlying soil. The surface area and terrain can be modelled on the basis of these data. The digital surface model (DSM) and the digital terrain model (DTM) describe the structures and the morphology of a landscape.
Close Monitoring of Temporal and Spatial Landscape Development
The cost of a countrywide survey using ALS is very high; therefore, regular updating of the data can be carried out only to a limited extent, so we have developed a more efficient method for updating the 3D landscape data. It is based on digital stereoscopic images which are routinely taken by the Swiss Federal Office of Topography, swisstopo. These stereoscopic images, which feature a high degree of spatial resolution, have been recorded with the "ADS80" digital sensor since 2005. As swisstopo repeats the recordings every three years, the resolution of the data is both spatially and temporally high. Within the context of the National Forest Inventory (NFI), we have developed a data processing procedure for calculating a comprehensive nationwide digital surface model (DSM) from the ADS80 stereoscopic images. DSMs now constitute an important data basis for assessing natural resources on a large scale with a high spatial resolution. In forests, for example, the height of the trees and the stocks accounts for a substantial part of the existing wood volume and biomass. Our method makes it possible to observe even small changes in the forest and other types of land cover over a relatively short period of time. Because the 3D calculations for Switzerland are carried out comprehensively, it is also possible to detect changes in the high mountains, e.g. in glaciers.