Forest physical sampling strategies for investigating noise mitigation benefits

Abstract

Acoustic attenuation rates in tree stands have been seen to vary considerably between measurements in various settings, with little hint as to the controlling mechanisms. Usual descriptors for a forest include tree species, stand age, and basal diameter per land surface area, properties that may not correlate with acoustic attenuation rates. As part of a recent forest attenuation measurement, we developed a forest sampling regimen aimed at indicating and distinguishing between three candidate effects: (1) scattering by resilient, wood material, (2) scattering by more compliant, leaf material, (3) refraction by canopy microclimate influence. Estimates of the wood material were made by an established point sampling process, in which significant tree trunks subtend a minimum angle at breast height. Canopy microclimate effect was characterized using percent optical closure of the upper canopy, canopy thickness, and ground vegetation height. Digital photographs aimed outward in four cardinal directions from each sample point were processed to segregate percentages of wood material, leaf material, and sky. We are currently exploring the connection between these parameters and measured attenuation rates in a single stand of woods. We propose that these parameters could offer improved correlation with measured attenuation rates between forests.