ACCURACY OF FOREST PARAMETERS DERIVED FROM MEDIUM FOOTPRINT LIDAR UNDER OPERATIONAL CONSTRAINTS

The objective of this study is to test the feasibility of nation-wide medium footprint airborne laser scanning (ALS) data for derivation of forest parameters. The comparison of canopy closure as one important parameter for many forest functions derived from ALS data and aerial photo interpretation was conducted. The present study was carried out in the framework of the Swiss National Forest Inventory (NFI). Three study areas of different size, topographic and forest characteristics were selected. In a first step, canopy height models (CHM) were obtained by subtracting the interpolated terrain altitudes of LiDAR (Light Detection And Ranging) DTM from the interpolated canopy altitudes (LiDAR DSM). Then a binary forest layer with CHM larger or equal 3 m was calculated according to the Swiss NFI forest definition. The Distinction between deciduous and coniferous forest (degree of composition) was performed using the surface cover classes (broadleaved tree, coniferous tree, larch) of the aerial photo interpretation of the NFI for 7,696 sample plots. In a second step, canopy closure derived from the aerial photo interpretation was compared to canopy closure calculated from binary CHM. The study reveals that the canopy closure is underestimated in the binary CHM from LiDAR data and highlights significant differences between coniferous and deciduous predominated forest plots and significant differences between compared canopy closure from winter and summer data. The study shows limitations of canopy closure derived from national LiDAR data but also stresses its practical relevance for many protective functions of forests in alpine conditions.