ACOUSTIC PROPAGATION THROUGH A TURBULENT ATMOSPHERE - EXPERIMENTAL CHARACTERIZATION

Experimental measurements of sound propagation through the atmosphere with particular emphasis on amplitude and phase fluctuations due to atmospheric turbulence are described. The experiment consisted of a source operated between 62.5 Hz and 8 kHz at heights of 1.5 and 30.5 m and an array of microphones 91.4-745 m from the source. The experimental site near Bondville, Illinois had good fetch and significant wind. The experimental acoustic propagation data is supplemented with meteorological measurements, including fluctuations in wind and temperature. The data has been analyzed in terms of the received amplitude and phase (relative to a reference microphone) forming a scatter plot in a complex plane, amplitude probability distribution, and transverse phase and amplitude structure functions. The scatter plot provides a qualitative measure of turbulence effects for applications requiring both phase and amplitude information. The amplitude probability distribution is more useful for noise estimates. The experimental structure functions are difficult to interpret at frequencies below 125 Hz due to the effects of background noise.