### ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

## 3aPAb3. Experimental observation of the effects of turbulence intermittency
on scattered sound.

**David I. Havelock
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*Inst. for Microstructural Sciences, Natl. Res. Council, Ottawa, ON K1A 0R6,
Canada
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Fully developed turbulence follows the well-known Kolmogorov spectrum and,
within the inertial subrange, is governed by a single parameter (epsilon) called
the viscous dissipation rate. Under stationary conditions the intensity of sound
scattered from turbulence follows an exponential distribution with mean
intensity I[inf 0] determined by (epsilon). In a more realistic turbulence
model, the viscous dissipation rate for a given scattering volume fluctuates
with a log-normal distribution. The corresponding fluctuations in I[inf 0] cause
the intensity distribution to deviate from the exponential distribution. In
particular, the tail of the distribution is raised, providing more frequent
occurrences of higher intensity levels. This effect impacts on target detection
probability in acoustic remote sensing applications. It is shown that the
deviations from an exponential distribution are clearly observable in direct
measurements of sound intensities within a refractive shadow near the ground.
The variance (sigma) of the fluctuations in the dissipation rate is estimated by
comparing the measured and theoretical distributions. It is also shown that
(sigma) cannot be obtained directly from short-term estimates of I[inf 0].