Table 2.

The distribution of return numbers (percentages) from airborne laser scans using a low-altitude drone under leaf-off and leaf-on conditions 51 days apart

	First	Second	Third	Fourth	≥ Fifth
Closed forest leaf off	43.0	31.1	17.2	6.8	1.9
Closed forest leaf on	63.7	27.8	7.1	1.2	0.2
Open forest leaf off	83.2	13.6	2.8	0.4	0.0
Open forest leaf on	86.8	11.5	1.5	0.2	0.0

The measurements were collected using the Brown Platform for Autonomous Remote Sensing and contrast a closed-canopy old-growth forest dominated by European beech (F. sylvatica) with an open area dominated by Norway spruce (P. abies) and silver fir (A. alba). Higher-order returns occur more frequently in closed-canopy forest due to complex vertical structure. The presence of leaf area reduces return numbers > 3