Atmospheric turbulence is inherently inhomogeneous and intermittent. Short
periods of high activity are embedded in longer periods of relative calm. L
ocal spatial and temporal changes in sound speed associated with this inter
mittency increase the likelihood of measuring large values of scattered aco
ustic signals. Previous work successfully predicted the probability density
functions (pdf's) of Fully saturated, scattered signals measured within an
acoustic shadow zone [Wilson et al., J. Acoust. Sec. Am. 99, 3393-3400 (19
96)]. The more general case of incompletely saturated scattering is conside
red in this paper; using the Rice-Nagakami distribution a theory is develop
ed. The predicted intensity pdf has two free parameters: one to describe th
e degree of intermittency and a second for the degree of saturation. For va
lidation purposes, outdoor propagation measurements were made over a flat,
hard ground at ranges of 146-283 m and at frequencies of 50-540 Hz. The sat
uration parameter was determined from the acoustic data and also estimated
from the turbulence conditions, The degree of saturation increased with fre
quency, and measured intensity pdf's were found to be in excellent agreemen
t with the theory. (C) 2001 Acoustical Society of America.