UAV Photogrammetric Surveys for Tree Height Estimation

Abstract

In the context of precision agriculture (PA), geomatic surveys exploiting UAV (unmanned aerial vehicle) platforms allow the dimensional characterization of trees. This paper focuses on the use of low-cost UAV photogrammetry to estimate tree height, as part of a project for the phytoremediation of contaminated soils. Two study areas with different characteristics in terms of mean tree height (5 m; 0.7 m) are chosen to test the procedure even in a challenging context. Three campaigns are performed in an olive grove (Area 1) at different flying altitudes (30 m, 40 m, and 50 m), and one UAV flight is available for Area 2 (42 m of altitude), where three species are present: oleander, lentisk, and poplar. The workflow involves the elaboration of the UAV point clouds through the SfM (structure from motion) approach, digital surface models (DSMs), vegetation filtering, and a GIS-based analysis to obtain canopy height models (CHMs) for height extraction based on a local maxima approach. UAV-derived heights are compared with in-field measurements, and promising results are obtained for Area 1, confirming the applicability of the procedure for tree height extraction, while the application in Area 2 (shorter tree seedlings) is more problematic.

Effects of different ground segmentation methods on the accuracy of UAV-based canopy volume measurements

“…With the combination of these two factors, U-Net trained based on DSM alone obtained the best canopy volume measurement with an RMSE of 0.410 m 3 . The RMSE of the UAV-based tree height measurements in this study was 0.644 m. An RMSE of 0.51 m was also obtained in young trees (Vacca and Vecchi, 2024). In a previous study, an RMSE of 0.28 m could be obtained using a high-resolution camera on a flat orchard (Mahmud et al, 2023), and an RMSE of about 0.3 m has been reported in a similar study (Wallace et al, 2016;Birdal et al, 2017;Krause et al, 2019).…”