Acoustic Scattering into Shadow Zones from Atmospheric Turbulence
Abstract
When acoustic scattering estimates are desired from atmospheric regions containing fully developed isotropic homogeneous turbulence, scattering formulas based upon statistical representations of the turbulence well represent the experimental results. However, there is a class of battlefield scenarios where these provisos of fully developed, isotropic and homogeneous sometimes do not apply. The example of this class that is most familiar is that of source and detector near the ground. At ground level, the wind velocity is zero, while at altitude it is not. Thus a gradient of wind velocity exists. There exists often a temperature gradient caused by heating or cooling of the air by contact with the ground. These gradients are recognized in propagation codes by modeling the atmosphere as stratified with each stratum bounded by planes parallel to the assumed flat ground. The anisotropy of the atmosphere near the ground recognized in propagation codes carries over into the generation of turbulence. The above discussion leads to the conclusion that anisotropy in turbulence is to be expected in scenarios played out near the ground, scenarios common to Army operations. The understanding that high sound levels in shadow zones (those regions in an acoustical field in which no sound can reach if the field is determined by ray theory) is caused by scattering from turbulence is very important. This importance arises from the possibility that shadow zone sensors may be used to achieve passive non-line-of-sight detection of enemy assets. This paper unites the above considerations by calculating the shadow zone signal level for a representative battlefield scenario using a structural model of turbulence.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1993
- Accession Number
- ADA381269
Entities
People
- George H. Goedecke
- Harry J. Auvermann
Organizations
- United States Army Research Laboratory