Physical and Descriptive Approaches to Medium-Induced Acoustic Fluctuation

Abstract

The purpose is to provide an introductory bridge between selected oceanographic concepts and their effects on the performance of sonar systems. The effect of Coriolis force and density stratification upon the motion of turbulence-produced fluid elements is examined under the steady state locally-barotropic condition. At any one point, a spectrum of density perturbations results, with a corresponding spectrum of sound- speed or delay-time fluctuations. The spatial correlation between fluctuations at two points depends on the averaging time used. Using a first-order stochastic model, two examples of fluctuation effects upon sonar system performance are given: the single receiving point mean square delay fluctuation as a function of target range, and regions of noise-dominated versus medium fluctuation-dominated sonar performance for a receiving aperture. The major conclusion is that sonar processing time, expressed in terms of oceanographic fluctuation power spectra, must be taken into account in estimating oceanographic effects upon sonar system performance.