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Fig. 1. Study site and the Ponsse Scorpion harvester used for the study (a), and the position of the two Ouster LiDARs, one GNSS antenna, and Novatel CPT7 installed on the boom of the Ponsse harvester (b). The Novatel CPT7 was behind the black box attached to the aluminium frame, not inside the black box.

Table 1. Technical specifications of the LiDAR systems used in this study.
LiDAR system Lasers wavelength (nm) Beam radius at exit (mm) Divergence (mrad)
Riegl VUX-1HA 1550 4.5 0.5
Riegl VUX-120 1550 NA 0.4
GeoSLAM Zeb Horizon RT 903 12.7 (horizontal) × 9.5 (vertical) 3.0 × 1.2, 300 kHz
Ouster OS0 (Rev 7) 865 5 6
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Fig. 2. Workflow for the plot level analysis and comparing consistencies among HMLS, DLS and harvester LiDAR points for low vegetation quantification in this study.

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Fig. 3. LiDAR point clouds showing vegetation points (a–d, i) by canopy height and ground points (e–h, j) by intensity values: DLS preharvest (a, e), DLS postharvest (b, f), HMLS preharvest (c, g), HMLS postharvest (d, h), and harvester LiDAR (i, j). View larger in new window/tab.

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Fig. 4. Harvester trajectory. During the harvesting operations, the trajectory of the harvester was monitored using a robotic total station.

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Fig. 5. Harvested area divided into 5 m × 5 m plots (grid cells) and selected plots for study containing point clouds (DLS post-harvest LiDAR point clouds).

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Fig. 6. Visualization of low vegetation structure: Point clouds (a), 10 cm voxels (b), and canopy height with grid size 10 cm (c) (Plot code: Plot 102: harvester LiDAR before harvesting operations).

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Fig. 7. Low vegetation height metrics (in meters) derived from three LiDAR systems (harvester LiDAR (Harv), HMLS, and DLS) before harvest (BH) and after harvest (AH): (a) maximum height, (b) 99th height percentile, (c) 95th height percentile, (d) 90th height percentile, (e) mean height, and (f) median height. Red points and red numerical values indicate the mean values.

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Fig. 8. Low vegetation points-occupied volume metrics (m3 per plot of 25 m2) from three LiDAR systems before and after harvesting. Volumes were estimated using the mean height method with 5 cm (a), 10 cm (b), and 20 cm (c) grids, and by fitting voxels of 5 cm (d), 10 cm (e), and 20 cm (f).

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Fig. 9. Low vegetation cover metrics from three LiDAR systems before and after harvesting. Cover was estimated using 5 cm (a), 10 cm (b), and 20 cm grids (c).

Table 2. Results of ANOVA and Kruskal–Wallis test on harvester, HMLS and DLS LiDAR for quantifying low vegetation attributes. Test values for one way ANOVA is F-statistic value (F) and for Kruskal–Wallis test Chi-square value (χ2). Short form written in the Test columns: K–W indicate Kruskal–Wallis test, ANOVA indicate one-way ANOVA, and logt, Sqrt, and Box-Cox represent the data transfomation process used to proceeed with one-way ANOVA test.
p-values in bold indicate statistical significance (p < 0.05).
Low vegetation attributes Pre-harvest Post-harvest
Test value p-value Adjusted p-value Test Test value p-value Adjusted p-value Test
Harvester
– DLS
HMLS
– DLS
HMLS
– Harvester
Harvester
– DLS
HMLS
– DLS
HMLS
– Harvester
Maximum height (m) 0.682 0.718 0.632 0.853 1.000 K–W 0.405 0.820 1.000 0.796 1.000 K–W
99th height percentile (m) 3.809 0.149 0.320 0.081 0.744 K–W 4.863 0.087 0.198 0.047 0.779 K–W
95th height percentile (m) 8.948 0.011 0.037 0.006 0.825 K–W 11.870 0.0026 0.0096 0.0021 0.960 K–W
90th height percentile (m) 8.138 0.0004 0.004 0.0008 0.855 ANOVA 18.570 9.25e-05 0.0005 0.0002 1.000 K–W
Mean height (m) 19.75 3.01e-08 0.0000 0.0000 0.716 Box-Cox 21.810 1.83e-05 0.0004 0.0000 0.771 K–W
Median height (m) 39.092 3.24e-09 0.0000 0.0000 0.669 K–W 40.517 1.59e-09 0.0000 0.0000 0.250 K–W
Volume with 5 cm grid (m3) 0.721 0.488 0.500 0.624 0.978 Sqrt 0.984 0.377 0.816 0.708 0.344 logt
Volume with 10 cm grid (m3) 0.058 0.943 0.999 0.948 0.958 Sqrt 1.343 0.264 0.951 0.428 0.273 Box-Cox
Volume with 20 cm grid (m3) 0.209 0.812 0.959 0.795 0.927 logt 1.611 0.204 0.980 0.232 0.317 Box-Cox
Volume with 5 cm voxel (m3) 75.229 2.2e-16 0.0000 0.0001 0.0000 K–W 66.027 4.59e-15 0.0000 0.0000 0.058 K–W
Volume with 10 cm voxel (m3) 38.793 3.76e-09 0.0000 0.0132 0.0005 K–W 4.618 0.0115 0.036 0.018 0.966 Box-Cox
Volume with 20 cm voxel (m3) 2.674 0.072 0.059 0.613 0.366 logt 0.755 0.472 0.993 0.507 0.573 Box-Cox
Cover with 5 cm grid 18.511 9.55e-05 0.0001 0.0010 0.846 K–W 42.358 6.33e-10 0.0000 0.0003 0.0085 K–W
Cover with 10 cm grid 47.828 4.11e-11 0.0000 0.0000 0.079 K–W 48.547 2.87e-11 0.0000 0.0021 0.0003 K–W
Cover with 20 cm grid 48.470 2.97e-11 0.0000 0.0000 0.025 K–W 42.812 5.05e-10 0.0000 0.082 0.0000 K–W