Alternatively, satellite-based remote sensing approaches can be effectively used to derive forest characteristics (e.g., canopy cover and above-ground biomass (AGB)) at a regional scale for a much lower cost and effort.
However, this method is costly, time-consuming, and labor intensive and, therefore, only appropriate for small forest stands. Traditionally, AGB and carbon stock have been estimated by measuring common dendrometric parameters such as Diameter at Breast Height (DBH) and height of trees in permanent field plots, and then applying allometric equations. UAV platforms can provide extremely high spatial resolution and low-cost data, along with high versatility, flexibility, and adaptability, making them one of the most useful and efficient platforms for obtaining remotely sensed data at a local scale. According to the findings of this study, it was concluded that UAV-RTK imagery can be considered a promising solution, but more work is needed before concluding its effectiveness in inaccessible areas.Ĭlose-range photogrammetry using unmanned aerial vehicle (UAV) platforms is an attractive technology to acquire accurate and timely information on target phenomena, such as trees. Root mean square error ( RMSE < 11%) indicated a reliable estimation at all the flight altitudes for trees height and crown diameter. Additionally, the means of crown diameter reported from field measurements and UAV estimation at all flight altitudes were not statistically different.
The results indicated that the means of tree height obtained from field measurements and UAV estimation were not significantly different, except for the mean values calculated at 100 m flight altitude. The crown height model ( CHM), derived from a digital surface model ( DSM), was used to estimate tree height, and an inverse watershed segmentation (IWS) algorithm was used to estimate crown diameter. UAV data acquisition was performed at three altitudes of 25, 50, and 100 m using a local network RTK system (NRTK). A total of 107 trees were subjected to field-measured dendrometric measurements (height and crown diameter). As it can tolerate harsh conditions, this species is highly appropriate for afforestation and reforestation projects. Arizona cypress is commonly planted as an ornamental tree. The study was conducted on a Cupressus arizonica (Greene., Arizona cypress) plantation on the Razi University Campus in Kermanshah, Iran. This study aimed to test the accuracy of a UAV-mounted GNSS RTK (real-time kinematic) system for calculating tree height and crown height without any GCPs. One of the main challenges of using unmanned aerial vehicles (UAVs) in forest data acquisition is the implementation of Ground Control Points (GCPs) as a mandatory step, which is sometimes impossible for inaccessible areas or within canopy closures.
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