ASSESSING EFFECTS OF LASER POINT DENSITY ON BIOPHYSICAL STAND PROPERTIES DERIVED FROM AIRBORNE LASER SCANNER DATA IN MATURE FOREST

Canopy height distributions were created from small-footprint airborne laser scanner data for mature coniferous forest in two forest areas in Norway. In total, 82 and 70 georeferenced field sample plots and 39 and 38 forest stands were measured in the two areas, respectively. The average sampling densities were 1.2 m -2 and 0.9 m -2 . Height percentiles, mean and maximum height values, coefficients of variation of the heights, and canopy density at different height intervals above the ground were computed from the laser-derived canopy height distributions from the first return data. The laser point clouds were thinned to approximately 1 point per 4 m 2 (0.25 m -2 ), 1 point per 8 m 2 (0.13 m -2 ), and 1 point per 16 m 2 (0.06 m -2 ). The mean difference and the standard deviation for the differences between laser-derived metrics derived from the original full density laser data and thinned data for the two areas were estimated and compared. For all comparisons, the maximum value of the canopy height distributions differed significantly between the full density laser datasets and the thinned data. The effects of different laser point densities on stand predictions of three biophysical properties of interest were also tested. The average standard deviation for mean tree height, stand basal area, and stand volume predicted at stand level showed only a minor increase by decreasing point density.