Large Scale Airborne Laser Scanning of Forest Resources in Sweden

The first large scale laser scanning project in Sweden for the purpose of forest inventory was started by a regional forestry board in central Sweden. The objective was to compare laser scanning with traditional operational methods for large area forest variable estimations. Laser data were acquired for a 50 km forest area in central Sweden with approximately 1.2 laser measurements per square meter. One field plot within each of 122 forest stands representing different forest types were used as training data. Mean tree height, mean stem diameter, basal area, and stem volume were predicted using regression functions with variables extracted from the laser canopy height distribution. Separate regression functions were built for Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and deciduous trees. The functions were applied at grid nodes for a grid covering the whole forest area and mean values of laser estimated forest variables were calculated within each forest stand. A special validation inventory of 29 forest stands was performed. The size of the forest stands used for validation ranged from 0.5 to 12 ha (median forest stand size was 1.3 ha). The relative RMSE at stand level was 5.0% (0.8 m) for mean tree height, 8.9% (1.9 cm) for mean stem diameter, 12.5% (3.0 mha) for basal area, and 14.1% (28 mha) for stem volume estimations. The results imply that estimations of forest variables using laser scanning give higher accuracies compared with using traditional methods.