Acoustic pulse propagation in an outdoor turbulent atmosphere

In a series of short-range experiments, attempts were made to relate the prevailing meteorological conditions to significant wave shape changes in a 2 ms acoustic pulse propagating over distances from 0.5 to 16 m. Unlike the findings in long-range studies involving time and spatial averages, no meaningful correlations between wind speed and acoustic pulse shape parameters were obtained. Pulse delays could be predicted provided detailed measurements of the wind speed were obtained. Observations showed that two adjacent paths could experience quite different propagation regimes. The geometry and pulse nature of the experiments described here restrict the scale of turbules in any cascade suggesting that a single turbule model may be applicable. Indeed using one or two effective turbules was capable of explaining many of the observations. One model approach used typical parameter values obtained from the literature or from measurements and by locating a single turbule at an appropriate distance from the source receiver axis, correctly generated the observed variety of wave forms. Alternatively, relying on measured data from one distorted pulse and the spatial wind profile, the model was used to determine subsequent pulse distortions. This was successful in predicting behavior in 76% of cases. (C) 2004 Acoustical Society of America.