REVERBERATION AND ATTENUATION IN A PINE FOREST

Measurements of reverberation and attenuation as a function of frequency have been made in a pine forest at ranges from 10-100 m, paying particular attention to diurnal variation in meteorological conditions and effects associated with receiver location. Up to 1 kHz, the measured excess attenuation is modeled tolerably well by a conventional point source calculation using a two-parameter ground impedance model. It is found that the observed variations in meteorological profiles do not produce significant changes in the measured 100-m attenuation at any frequency. It is proposed that high-frequency attenuation and reverberation for ray paths below the foliage canopy are dominated by multiple scattering among the tree trunks. This is modeled numerically by a stochastic particle bounce procedure. The results of calculations indicate the relative importance of multiple scattering in reverberation and attenuation. However, the model is unable to verify the strong height dependence shown by the measured attenuation. The results suggest an interaction between ground effect and trunk scattering that is more complicated than simple addition as proposed hither-to. It is shown that the measured attenuation is considerably underpredicted by the Dutch-Scandinavian noise prediction scheme. The A-weighted emission level of road traffic noise transmitted through 100-m woodland of this type is significantly lower than that transmitted over 100-m pasture.