Acoustic Effects of Trees Simulated by a Finite-Difference Time-Domain Model

Abstract

The simulation of sound propagation in and around forest areas requires a detailed understanding of the acoustic properties of trees. Therefore, the acoustic properties of laser-scanned real trees and idealized trees are studied by means of a three-dimensional finite difference time domain (FDTD) sound propagation model. The aim is to gain functional relationships between backscattered and transmitted sound pressure levels and selected tree characteristics. The choice of the model type enables the simultaneous consideration of multiple reflections and diffraction of sound waves. The spatial resolution of 5 cm admits a frequency range up to 1350 Hz and the resolution of the trunk and major branches. The simulated sound pressure signals are detected by a virtual microphone array in front and behind an infinitely long row of trees, respectively. Regarding the density of tree material within a volume, thin objects reflect less sound energy than dense objects, which in contrast have a noticeable acoustical effect on the transmission loss. The relations are provided by a set of empirical equations.