For the beginning of my literature review I started by presenting the fundamentals of acoustics and the way sound waves behave and interact with their surroundings. The aim is to establish different terms which are going to be used considered and used throughout the report.
The Behaviour of Sound in Space
Acoustics can be defined as the science of sound [1]. Sound waves, like all mechanical waves, as they interact with their surroundings they can experience different effects such as absorption, reflection, scattering, diffusion, diffraction and more. When writing this section of the literature review, the aim was to understand how a forest would act as a system and hence, how sound would behave within such an environment.
The absorption coefficient of a tree can determine the energy lost when a wave bounces on its surface, and its effect on the harmonic content of the reflected ray. The scattering indicates how the angle of reflection changes depending on the roughness of the surface and how sound diffuses across the space. Diffraction allows sound to travel around the tree trunk making the source audible to the receiver even when the direct path is blocked. In a forest, low frequencies will diffract due to their longer wavelength, while higher ones will scatter towards different directions [2]. Several of these phenomenons can be noticed through studying, the direct path, early reflections and reverberations of Impulse Responses (IRs) in a known system.
Conclusion
After obtaining an understanding of the way sound behaves in space, it is time to investigate more specifically how certain effects apply in a forest. Next I am going to look into literature that studies the way absorption and scattering takes place in forests, Trees and other vegetation.
Figure: Direct sound and early reflections in an enclosed space taken by IKoustic [3]
[1] Kuttruff, Heinrich. 2006. Acoustics: An Introduction. CRC Press.
[2] Reethof, G., O. H. McDaniel, and G. M. Heisler. 1977. “Sound Absorption Characteristics of Tree Bark and Forest Floor.” In In: Heisler, Gordon M.; Herrington, Lee P., Eds. Proceedings of the Conference on Metropolitan Physical Environment; Gen. Tech. Rep. NE-25. Upper Darby, PA: US Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 206-217. Vol. 25. https://www.fs.usda.gov/treesearch/pubs/11547.
[3] IKoustic. Acoustic glossary, 2019. URL https://www.ikoustic.co.uk/acoustic-glossary
George Sarantinos 