Statistical characterization of sound propagation along near-vertical paths in a turbulent atmosphere

Abstract

Most previous research on sound propagation in the atmosphere has focused on nearly horizontal propagation paths, with the sources and receivers close to the ground. Along such paths, refraction by wind and temperature gradients, and scattering of sound by small-scale turbulence, are known to be important and have been studied extensively during the past couple decades. Sound propagation from elevated sources is fundamentally different because the atmospheric motions are larger, more coherent, and driven by different types of instabilities. The corresponding research is needed to address the ability of ground-based acoustic microphone arrays to detect and track elevated sound sources, as well as the ability of elevated arrays to detect and localize ground-based sources. In this paper, near-vertical sound propagation through a turbulent atmosphere is studied using approaches and methods developed in wave propagation through random media. The statistical characteristics of sound signals for near-vertical propagation such as the log-amplitude and phase fluctuations, angle-of-arrival variance, transverse and longitudinal spatial coherence, and temporal and frequency coherence are calculated and analyzed. The results obtained are compared with those for near-horizontal sound propagation.