Generating random sound speed fields in water using heating or cooling

Abstract

Both heating and cooling techniques have been developed for generating random sound speed fields along a ten meter acoustic propagation path in a 14 m tank having a 3.7 × 3.7 m cross section. A 1.5-MHz cw signal was propagated along this path for the purpose of studying high-frequency acoustic signal fluctuations in a random medium. Previous investigators of acoustic fluctuations have produced random sound speed distributions by locating heating elements beneath the propagation path. Localized heating of water generates bubbles due to degassification, and it has been suggested that observed fluctuations may be due to resonant scattering by these rising microbubbles [J. A. Neubert and J. L. Lumley, J. Acoust. Soc. Am. 64, 1148–1158 (1978)]. Preliminary qualitative results indicate that statistically similar random sound speed fields generated by heating from below or by cooling from above produce similar acoustic fluctuations.