Sound propagation at low altitude

The propagation of sound waves at low altitude was studied in order to determine the perturbations due to the atmosphere. A physical model for sound propagation was developed, and used to establish a computer program which can take into account in three dimensions any characteristics of wind, temperature, and hygrometry, as well as their temporal fluctuations. Meteorological measurements were performed. Sound pressures were obtained using microphone lines on the order of a kilometer. Spectra, correlations, and coherence were determined. The measurements show that a numerical analysis which takes into account unsteady and three-dimensional aspects of the propagation is necessary. A better knowledge of the atmospheric turbulence regimes is necessary to determine the correlation between experimental and numerical results.