Understanding the dynamic properties of trees using the motions constructed from multi-beam flash light detection and ranging measurements.

Abstract

Measuring the three-dimensional motion of trees at every position remains challenging as it requires dynamic measurement technology with sufficient spatial and temporal resolution. Consequently, this study explores the use of a novel multi-beam flash light detection and ranging (LiDAR) sensor to tackle such a sensing barrier. A framework is proposed to record tree vibrations, to construct the motions of tree skeletons from the point-cloud frames recorded by the LiDAR sensor and to derive the dynamic properties of trees. The feasibility of the framework is justified through measurement on a <i>Ficus microcarpa</i> under pull-and-release tests. The relative differences for the first two modal frequencies between the LiDAR and linear variable differential transformer measurements in the displacement Fourier spectra are 0.1% and 2.5%, respectively. The framework is further adopted to study the dynamic response of different trees subjected to typhoons, including a <i>Liquidambar formosana</i>, three <i>Araucaria heterophylla</i> trees, <i>a Sterculia lanceolata</i>, a <i>Celtis sinensis</i>, a <i>Tabebuia chrysantha</i> and a <i>Cinnamomum camphora</i>. Results suggest that broadleaved trees might exhibit vibration in a wide frequency band, whereas the coniferous trees could follow a distinct dominant frequency.