Testing the usability of truncated angle count sample plots as ground truth in airborne laser scanning-based forest inventories

Airborne laser scanner (ALS)-based forest inventory method usuallyadopt a laser canopy height distribution approach in which forestcharacteristics are predicted using measures such as percentilesof the distribution of laser canopy heights across a fixed area.The method requires a ground-truth sample of accurately measuredfield plots. One possibility for reducing the costs lies inthe use of existing field plots for ground-truth purposes. Themost obvious alternative in Finland would be to use truncatedangle count sample plots of the National Forest Inventory ormore locally data of checking of inventory by compartments.Due to the lack of suitable angle count ground-truth data andcorresponding laser data, we tested this possibility using dataon fixed-area sample plots, in which tree locations were simulated.The trees for a truncated angle count sample plot were thenchosen and the resulting data together with the characteristicsof an ALS-based canopy height distribution were used to constructregression models to predict stem volume, basal area, stem number,basal area median diameter and height. The accuracy of the standattributes was found to be almost as good as in the case ofmodels of fixed-area plots.