Accession Number : ADA328618

Title :   First-Order Acoustic Wave Equations and Scattering by Atmospheric Turbules.

Descriptive Note : Final rept. Mar 91-Dec 94,

Corporate Author : ARMY RESEARCH LAB ADELPHI MD

Personal Author(s) : Goedecke, George H. ; DeAntonio, Michael ; Auvermann, Harry J.

PDF Url : ADA328618

Report Date : AUG 1997

Pagination or Media Count : 42

Abstract : A new turbulence model is used to describe the acoustical scattering from atmospheric turbulence. A complete set of fluid equations, including the heat flow equation with zero conductivity, is presented for an ideal gas atmosphere. From this set, a complete set of coupled linear differential equation is derived for the acoustic pressure, temperature, mass density, and velocity in the presence of stationary turbulence. From these acoustic wave equations, expressions for acoustic scattering cross sections are derived for individual localized stationary scalable turbules of arbitrary morphology and orientation. Averages over random turbule orientations are also derived. Criteria for comparability of orientationally averaged turbules with different envelope functions are presented and applied, and cross sections for Gaussian and exponential envelopes are compared. The azimuthal dependence of the velocity scattering cross section for a spherically symmetric nonuniformly rotating turbule is illustrated. It is shown that, for incoherent scattering, a collection of randomly oriented turbules of arbitrary morphology may be replaced by an 'equivalent' collection of spherically symmetric, nonuniformly rotating turbules with randomly directed rotation axes.

Descriptors :   *ACOUSTIC WAVES, *TURBULENCE, *ACOUSTIC SCATTERING, *ATMOSPHERE MODELS, ATMOSPHERIC TEMPERATURE, TURBULENT FLOW, ATMOSPHERIC MOTION, GAS DYNAMICS, ACOUSTIC SIGNALS, ACOUSTIC VELOCITY, SOUND PRESSURE, WAVE EQUATIONS, LINEAR DIFFERENTIAL EQUATIONS.

Subject Categories : Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE