Understanding the dynamic properties of trees using the motions constructed from multi-beam flash light detection and ranging measurements
Wai Yi Chau, Cheng Ning Loong, Yu-Hsing Wang, Siu-Wai Chiu, Tun Jian Tan, Jimmy Wu, Mei Ling Leung, Pin Siang Tan, Ghee Leng Ooi
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 Ficus microcarpa 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 Liquidambar formosana , three Araucaria heterophylla trees, a Sterculia lanceolata , a Celtis sinensis , a Tabebuia chrysantha and a Cinnamomum camphora . Results suggest that broadleaved trees might exhibit vibration in a wide frequency band, whereas the coniferous trees could follow a distinct dominant frequency.