The Influence of Scattering Volume on Acoustic Scattering by Atmospheric Turbulence
Abstract
From a complete set of fluid equations, a complete set of coupled linear differential equations for the acoustic pressure, temperature, mass density, and velocity in the presence of stationary turbulence may be derived. To first order in the turbulent temperature variation and flow velocity, these coupled acoustic equations yield an acoustic wave equation given in the literature. Further reduction of this wave equation results in a second equation given in the literature which is good for turbulent length scales alpha much greater than the acoustic wavelength lambda. The length scale alpha(s) of the scattering volume is found to be just as important as alpha and lambda in predicting the general behavior of acoustic scattering by turbulence. In particular, if alpha < < alpha(s), then the first Born temperature and velocity scattering amplitudes for any ratio alpha/lambda are the usual ones predicted by the first equation, and both the forward and backward velocity scattering are essentially zero for solenoidal turbulent flow velocity. The latter is not true if alpha > alpha(s). If a >/= alpha(s) > > lambda, then the first Born scattering amplitudes are those predicted by the second equation. If lambda >/= alpha >/= alpha(s), other forms result for the scattering amplitudes. Implications of these findings for predicting results of acoustical scattering experiments where the scattering volume is often ill defined are discussed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1994
- Accession Number
- ADA378412
Entities
People
- George H. Goedecke
- Harry J. Auvermann
- Michael Deantonio
Organizations
- United States Army Research Laboratory