GCPs-Free Photogrammetry for Estimating Tree Height and Crown Diameter in Arizona Cypress Plantation Using UAV-Mounted GNSS RTK

One of the main challenges using unmanned aerial vehicles (UAVs) in forest data acquisition is implementation Ground Control Points (GCPs) as a mandatory step, which sometimes impossible for inaccessible areas or within canopy closures. This study aimed to test accuracy UAV-mounted GNSS RTK (real-time kinematic) system calculating tree height and crown without any GCPs. The was conducted on Cupressus arizonica (Greene., Arizona cypress) plantation Razi University Campus Kermanshah, Iran. cypress commonly planted an ornamental tree. As it can tolerate harsh conditions, this species highly appropriate afforestation reforestation projects. A total 107 trees were subjected field-measured dendrometric measurements (height diameter). UAV performed at three altitudes 25, 50, 100 m local network (NRTK). model (CHM), derived from digital surface (DSM), used estimate height, inverse watershed segmentation (IWS) algorithm diameter. results indicated that means obtained field estimation not significantly different, except mean values calculated flight altitude. Additionally, diameter reported all statistically different. Root square error (RMSE < 11%) reliable According findings study, concluded UAV-RTK imagery be considered promising solution, but more work needed before concluding its effectiveness areas.