## 2 Materials and Methods
### Canopy Cover Data  
To collect information on the three-dimensional structure of the canopy cover, a DJI Mavic 2 Pro drone flight was carried out at an altitude of 80 m before the harvesting operations. The drone was additionally equipped with a TOPODRONE DJI Mavic 2 Pro PPK Upgrade Kit [22]. This setup allowed a high-precision aerial survey to be performed without ground control points (GCP); however, to calibrate the focal length of the camera and to check the quality of the positional accuracy, 12 GCP were distributed in open unobstructed locations over the study area and measured with a multiband Emlid REACH RS2+ RTK GNSS receiver [23] with a 1 cm accuracy. The precise coordinates of the image centers were obtained in post-processed kinematic (PPK) mode after the images and logs from the TOPODRONE DJI Mavic 2 Pro PPK Upgrade Kit were combined in TOPODRONE post-processing software [24].  
The double-grid flight pattern was employed using a consumer-grade UAV (DJI Mavic 2 Pro, Shenzhen, Guangdong, China) equipped with a Hasselblad L1D-20c RGB camera. The flights had an 80% overlap, 70% sidelap, and a camera angle of 90 degrees. The flight was automated using the Pix4 Dcapture application. The unmanned aerial vehicle (UAV) data were processed in Agisoft Metashape Professional software [25] using a structure-from-motion (SfM) workflow, which is a photogrammetric technique for estimating three-dimensional structures from two-dimensional image sequences. The images were aligned, and the GCP coordinates were imported from TOPODRONE Post Processing [24]. We performed bundle adjustment in the selected coordinate system  
\begin{table}
\begin{tabular}{c c} \hline
**Technical Specification** & **Description** \\ \hline GNSS signals received & GPS L1, L2, L2C, L5; GLONASS L1, L2, L3; Galileo E1, E5a, E5b, E6; \\  & BeiDou B1, B2, B3; QZSS L1, L2C, L5, L6; NavlC L5 \\ Channels & 672 \\ Positioning modes & RTK, DGNSS, Static, Rapid Static, PPP \\ RTK accuracy & 8 mm + 0.5 ppm horizontal; 15 mm + 0.5 ppm vertical \\ DGNSS accuracy & 30 cm (95\% confidence) \\ Time to first fix (TTFF) & Cold start: \textless{60 s}; warm start: \textless{30 s}; hot start: \textless{10 s} \\ Data update rate & Up to 20 Hz \\ Operating temperature range & \(-40\) °C to \textless{75 °C} \\ Storage temperature range & \(-40\) °C to \textless{80 °C} \\ IP rating & IP68 (protected against dust, sand, and temporary immersion in water) \\ Battery life & Up to 10 h (RTK Rover) \\ Bluetooth & Bluetooth 4.0 and 2.1 + EDR compliant \\ Size & 17.8 cm \(\times\) 11.4 cm \(\times\) 4.4 cm \\ Weight & 1.07 kg (with internal battery) \\ \hline \end{tabular}
\end{table}
Table 1: Technical specifications of the Trimble R12 GNSS receiver.  
(EPSG::3903: ETRS89/TM35 FIN(N,E) + N2000 height) and built a dense point cloud with default values of \"Ultra high quality\" and \"mild\" depth filtering. The total error of the image block georeferencing was 7.76 cm. The spatial resolution of the digital surface model (DSM) was 2.7 cm. Points were classified as either \"ground\" or \"other\"; then, the digital elevation model (DEM) and the DSM (Figure 3) were constructed. Further, subtracting the DEM from the DSM allowed the canopy height model (CHM) to be calculated.