The coefficient of variation for a series of sound pulses and the correlation function for successively received sound pulses are evaluated for arbitrary pulse length, using the assumption that the correlation function of the refractive index inhomogeneities is expressible as the product of time‐ and space‐dependent functions. For the case of pulse length much less than the time constant of refractive index correlation function, the coefficient of variation is found to be independent of the pulse length, and the pulse‐correlation function is found to be identical with the time‐dependent part of the refractive index correlation function. Comparison is made with data obtained from Sheehy. An approximate calculation shows that the motion of source and receiver will distort the pulse‐correlation function so that little information can be obtained from the data concerning the time dependance of the refractive index.