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Wilkes, Phil A comparison of terrestrial LiDAR and photogrammetry for rapid characterisation of fine scale branch structure Poster
Phil Wilkes1,4, Alexander Shenkin2, Mathias Disney1,4, Yadvinder Malhi2 and Lisa Patrick Bentley3
(1) Department of Geography, UCL, Gower Street, London, WC1E 6BT, UK(2) Environmental Change Institute, University of Oxford, South Parks Road, Oxford OX1 3QY, UK(3) Department of Biology, Sonoma State University, 1801 E. Cotati Ave., Rohnert Park, CA 94928, USA(4) NERC National Centre for Earth Observation, UK

Fine scale branch architecture (e.g. where branch diameter <5 cm) is laborious to measure for standing trees and is therefore often overlooked. However measurements of key traits related to fine scale branch architecture such as branch surface area and volume are crucial for estimating whole-tree traits and testing hypotheses relating tree architecture form and function. One option to collect detailed fine-scale branch architecture is to manually harvest branches and then measure them on the ground; however, hand measurements are laborious, limiting the size and number of branches that can be measured. Here we compare two semi-automated methods to capture fine-scale branch architecture; one using terrestrial LiDAR (TLS) and the other photogrammetry.. Both methods generate a 3D point cloud to which quantitative structural models (QSM) are applied to parameterise branch architecture e.g. volume, surface area, branch angle. The TLS workflow scans 3-6 branches consecutively where the scanner is moved around the scene. Branches are then extracted and denoised using a local filtering method to provide the cleanest point cloud for reconstruction. The photogrammetric method uses a Structure from Motion (SfM) solution to generate a point cloud where branches are imaged on a revolving platform. Both methods produce high quality measurements i.e. multiple points per cm. However, TLS tends to overestimate branch tip width compared to manual measurements, less so for photogrammetry. We explore here why these differences occur and we also suggest new metrics that can be derived from these approaches that may allow for improved uses of branch architecture traits to answer ecological questions related to the scaling of tree form and function.