Edward R. Maniet, Jr.
Grad. Prog. in Acoust., Penn State Univ., Appl. Sci. Bldg., University Park, PA 16802
Experimental studies investigated the effects of atmospheric surface-layer convective turbulence on the amplitude fluctuations of line-of-sight sound propagation. Several pure tones between 25 and 125 Hz were continuously monitored at a distance of 758 m for periods of 4 to 6 days by two microphones at heights varying between 0 and 8 m. Simultaneous surface-layer micrometeorological measurements were made at the same site. Statistics of the acoustic transmission loss (TL) were analyzed along with the sensible heat flux (Q), a measure of the strength of convectively driven turbulence. It was observed that only the lowest studied frequency, 27.6 Hz, showed any dependence on the value of the sensible heat flux. The average standard deviation of the TL for the 27.6 Hz tone was twice as great under strongly convective conditions than under conditions with weak or no convection. It is suggested that turbulent static pressure fluctuations associated with surface-layer thermal plumes were responsible for the increased TL variability at 27.6 Hz.