ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1aPA5. The effect of turbulence drift on acoustical scattering into a shadow region.

Michael R. Stinson

Inst. for Microstruct. Sci., Natl. Res. Council, Ottawa, ON K1A 0R6, Canada

The turbulence structures responsible for acoustical scattering in the atmosphere are not static and evolve in time. As a first approximation, a uniform drift of the turbulence with the prevailing winds, consistent with Taylor's hypothesis, can be anticipated. This drift can be accommodated through an extension of the Green's function parabolic equation (GF-PE) approach. Normal implementations of the GF-PE compute the sound field assuming a static realization of turbulence. Such calculations can be repeated, though, for successive realizations of a turbulent atmosphere, with each realization corresponding to an additional shift in space of the initial turbulent structure. The resulting series of sound field ``snapshots'' shows the evolution of the sound field as the turbulence drifts. Recent simulations using the GF-PE have examined scattering by drifting turbulence into an acoustical shadow, formed during upward refracting conditions, and the time evolution of the scattered field will be presented. The nature of these time variations is relevant to the use of beamforming arrays in an acoustic shadow. Some observations about predicted array responses will be discussed.