TIME AUTOCORRELATION OF SONIC PULSES PROPAGATED IN A RANDOM MEDIUM

Measurements were made of the random variation produced in the amplitudes of sonic pulses propagated through a water medium in which was induced a nearly homogeneous random perturbation in temperature. The measurements were carried out at frequencies of 480 kHz and 1.42 MHz for transmitter to receiver separations ranging from 1638 to 7658 in. The amplitude variations of the received pulses were analyzed to determine their time autocorrelation and variance as functions of range, i.e., transmitter to receiver separation and frequency. It was found that the time autocorrelation of the sonic pulse amplitudes was equivalent to that measured for the temperature microstructure. The variance in sonic pulse amplitude was determined as a function of range at both operating frequencies. These findings are compared with the theoretical findings of Mintzer and Bergmann. An equivalence of the time autocorrelation of sonic pulse amplitude and temperature microstructure predicted by theoretical considerations is indeed supported by, experimental findings; however, the observed dependence of variance on range fell between the linear dependency predicted by Mintzer and the third power dependency predicted by Bergmann. This was expected, since the frequency distance and parameters were in between the extremes assumed in those derivations. © 1969, Acoustical Society of America. All rights reserved.