Abstract:

It is often assumed that propagation models developed for ocean acoustics can be applied with minimum modification to atmospheric sound propagation. Experience shows that one often finds subtle but significant problems that can lead to serious numerical (prediction) errors, even in cases where the atmospheric environmental inputs seem similar to those in ocean acoustics. In this paper three sources of error and methods for reducing the errors to acceptable levels are discussed. The first error was recently discovered by Erik Salomons [E. M. Salomons, ``Improved Green's function parabolic equation (GFPE) method for atmospheric sound propagation,'' J. Acoust. Soc. Am. (submitted)] and concerns the failure of standard FFT algorithms when applied to atmospheric split-step parabolic equation calculations for propagation over hard ground surfaces. The second problem concerns accurate numerical treatment of the surface wave that is excited by a point source over a locally reacting ground surface. The last issue discussed is the need for improved approaches to implementing an outgoing-wave boundary condition in calculations of long-range outdoor sound propagation. Numerical examples are presented showing the effect of the errors on the predicted signal. [Work supported by the Army Research Laboratory and the Pennsylvania State University Applied Research Laboratory.]