Interference of the direct and two ground-reflected waves in a turbulent atmosphere

The interference of the direct wave from a source to receiver and that reflected from the ground is one of the main phenomena in short-range sound propagation in the atmosphere. This article studies ground interference in a turbulent atmosphere when, in addition to the direct wave, two ground-reflected waves arrive at the receiver. The multiple reflections occur in the presence of the sloped ground such as a hill or other terrain feature. The mean-squared sound pressure at the receiver depends on three factors, which characterize coherence between the three waves considered in a turbulent atmosphere. These coherence factors are expressed in terms of the geometrical parameters of the problem and effective spectrum of atmospheric turbulence. Numerical calculations demonstrate that the additional reflected wave from the sloped ground increases the number of the interference minima and maxima in the mean-squared sound pressure as a function of frequency. Due to atmospheric turbulence, the mean-squared sound pressure significantly increases at the minima and decreases at the maxima. These effects become greater with increasing frequency and turbulence intensity.