Miniature UAVs and Photogrammetry--A Novel Approach to Collecting Aerial Inspection Data from Mature Broadleaf Trees.

Background: Production of high-quality 3D models of trees has a practical application in arboriculture, allowing the assessment, measurement, and recording of aboveground structural features of individual trees. Commercially available hobby UAVs (uncrewed aerial vehicles) with integrated cameras in combination with a low-cost photogrammetry software package can produce high-definition 3D models of tree structures with low financial investment. Methods: Our study compared an established orbital flight strategy and 2 novel close-range flight strategies for collecting digital imagery to produce 3D models of features of interest (FOIs) in trees. We used 3 separate tests to establish if these different flight strategies resulted in reliable, measurable, and complete models for FOIs in mature broadleaf trees. Results: Our study substantiated the findings of previous studies, in that a well-planned, automated orbital strategy of flight can render full models of trees from which accurate measurement of dimensions can be obtained. A flight strategy involving collecting clusters of images from different angles whilst the UAV stayed in one location was trialled, and the resulting models were typically incomplete and of low quality. However, the second close-range strategy of hand-flown missions running parallel with the FOI yielded highly detailed, complete models from which observations of the FOI's surface and accurate measurements of its dimensions could be obtained. Conclusions: We conclude that there are substantial opportunities for the use of low-cost UAVs to undertake visual tree assessments of the aerial parts of trees, subject to ease of access to the feature and the right choice of flight strategy. [ABSTRACT FROM AUTHOR]