Scaled Laboratory Experiments of Shallow Water Acoustic Propagation: Calibration Phase

Abstract

Laboratory experiments in underwater acoustics aim at the validation of theoretical acoustic propagation models in well controlled environments. The experimental tank of the LMA Laboratory provides an ideal environment for testing long range propagation codes. The tank is relatively long and the water depth is adjustable in order to simulate real propagation experiments in environments of variable depths. The purpose of this paper is to describe the experimental procedure for the realization of a long range propagation experiment in an experimental tank, using sources of appropriate frequency. The bottom of the tank was covered by a thick layer of fine sand with well known properties to simulate a real.stic sea-bed. It was supposed to be horizontal and perfectly flat without any ripples on the surface. The measured, monochromatic continuous wave, signals are processed to provide the acoustic field at various depths and ranges in the tank in decibels, and are compared with theoretical models based on normal-mode theory and parabolic equations. The comparison in the cases studied, which corresponded to shallow water transmissions are encouraging. Technological problems and scaling factors are also discussed.