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