Acoustic sounding the statistics of fluctuating fluid

The lateral correlation of a spherical wave propagating outdoors and in a model atmosphere was measured in order to determine statistical parameters of the propagation medium. Wind-and temperature data are monitored at the same time, and the structure constants and outer scale of tubulence are calculated. The acoustic correlation is evaluated using the parabolic equation method and assuming a von Karman spectrum of turbulence. The acoustic measurements yield comparable results to the statistical parameters derived independently from the wind and temperature measurements. The deviations are due to the fact that in the present theory a von Karman spectrum of turbulence is assumed which is not always met in the real experimental setup. On the other hand the local determination of the time history of wind and temperature is less representative than the spatial average which is performed by the tomographic sensing of the acoustic wave.