Geometrical theory of sound propagation in the atmosphere

Global morphology of infrasound propagation

“…Classical ray tracing methods assume the propagation of a plane parallel acoustic wave front in a locally linear medium. The equations of propagation [e.g., Groves , 1955a] are where the r is the position of the wave front and k is the wave front normal unit vector. Here c is the sound speed and u is the wind vector, both of which are implicit functions of r .…”

“…This dependence has even lead several researchers to suggest that infrasound can be used as an atmospheric remote sensing tool in the way acoustic tomography is used in oceanography and seismology [e.g., Groves , 1955b; Rind and Donn , 1975; Donn and Rind , 1979]. In fact, the existence of the stratopause was first hypothesized in the early 1920s based on the audibility of explosions at large distances [ Groves , 1955a; Brown and Hall , 1978].…”

Modified ray-mode (phase) theory: Understanding counter-wind propagation effects from atmospheric explosions

“…Physically we expect that in a range-independent, perfectly stratified steady-state model atmosphere, K measured at the observer should equal the value generated at the source and for such a medium the beamed azimuth from the source, f, is an additional kinematic constant of the propagation (Groves, 1955;Lindsay, 1960).…”

“…Starting from the geometrical acoustics, ray theory limit, it is well known that we must add the respective zonal, meridional and vertical mean wind components (u,v,w) as presented in Jones (1969), in Thompson (1972) and in vector form in Landau and Lifshits (1987) to the wave normal path, group velocity equations with group velocity speeds {c gx ,c gy ,c gz } in the {x,y,z}, Cartesian coordinate system which for a perfectly stratified, steady-state atmosphere and for almost-plane waves (b 51) with no changes in the wave normal propagation heading, f, reduces to (Milne, 1921;Groves, 1955;Lindsay, 1960;Thompson, 1972;ReVelle, 2010ReVelle, , 2004:…”

“…All paths with effective phase speeds Adiabatic, thermodynamic mean sound speed and horizontal wind speed profiles exceeding the maximum of the effective sound speed will be lost from the duct whereas all paths with effective phase speeds less than the maximum will be retained in the duct (Groves, 1955).…”