Mapping Swedish Fells
At SLU in Umeå, researchers are developing new techniques for automated mapping of land cover.
Two examples of these new techniques are refined satellite image classification and the use of data from airborne laser scanning. Researcher Heather Reese at SLU has explored possibilities of mapping forest and alpine vegetation in Sweden based on satellite images. The study area is situated in Vindelfjällen, Västerbotten County in northern Sweden.
Heather Reese used aerial photo-interpreted sample plots from two environmental monitoring programmes, NILS (National Inventory of Landscapes in Sweden) and THUF (Terrestrial Habitat Follow-up) as reference data.
‘In a satellite image, different types of vegetation are represented by different colours. By means of aerial photo-interpretation we can first identify the vegetation, for instance mesic or dry heath, and find the corresponding land areas in the satellite image. Then a computer program is used to identify all remaining pixels with the same colour, thereby identifying all places in the satellite image of a certain vegetation type. In this way we can create a map,’ says Heather Reese.
The most accurate maps are generated when information on the topography is included.
‘The reason for this is probably due to the very elevation-dependent vegetation. So far I have used an elevation model from Lantmäteriet (the Swedish mapping, cadastral and land registration authority). Now we will test other sources of topographic data such as laser scanning which generates a high-resolution 3D image of the landscape. Combining these data with satellite data may be a useful method in the future to create maps of forest and alpine vegetation,’ says Heather Reese.
Within the research programme EMMA (Environmental Mapping and Monitoring with Airborne laser and digital images) led by SLU, laser scanning has been tested for estimating and mapping the amount of biomass near the tree line in Abisko, Norrbotten County in northern Sweden.
‘Laser scanning is an excellent technique for mapping of the tree line. It’s objective, contrary to aerial photo-interpretation. I consider laser scanning along with satellite image-interpretation as a hot future monitoring method,’ says Håkan Olsson, professor at SLU.
Writer:
Karin Nilsson
Published:
2011-11-29
Vegetation map of Vindelfjällen, Västerbotten County, northern Sweden. Source: Heather Reese/SLU
FACTS on Satellite Images and Laser Scanning
Satellite images and laser scanning are complementary data sources.In a satellite image, different types of vegetation are shown with different colours. It’s a faster, easier and cheaper technique than aerial photo-interpretation.
Laser scanning gives information on the 3D structure of land and vegetation. 100 000 measurements per second with decimeter accuracy provide information on vegetation location, height and density. A forest’s biomass can then be calculated through the known relation between tree trunk diameter and tree height.