Dept. of Aerosp. and Mech. Eng., Boston Univ., 110 Cummington St., Boston, MA 02215
A novel technique for approximate computation of transient waveforms through weakly inhomogeneous media is described. It has some of the features of ray acoustics formulations, but largely circumvents the problems associated with caustics and allows the incorporation of diffraction effects. The prototype for a single step in propagation range is that where the acoustic pressure is specified as a function of time and lateral position on a planar surface, with the desire to determine the acoustic pressure on some further surface at a distance (Delta)x in the general direction of propagation. To determine the pressure versus time at a typical point on the second surface, an approximate integral solution is developed in terms of a Green's function for a point source in the inhomogeneous medium. Such a Green's function is determined by matching a ray acoustics solution in the far field to Blokhintzev's well-known solution for a point source in a homogeneous moving medium. Although the overall wave field may encounter a caustic in the intervening slab, such is not as likely to occur for the Green's function because of its intrinsic spherical spreading.