Complex ray tracing algorithm for infrasound propagation in the atmosphere

Abstract

A classical long standing challenge for the infrasound research community is explaining frequently observed infrasound arrivals into shadow zones. This arrivals can be obtained by generalising standard ray method to complex ray tracing, which takes into account diffraction effects. This method is applied to long range infrasound propagation in a stratified and moving atmosphere by a three step numerical algorithm computing both real and complex eigenrays. First, real rays shooting allows to locate caustics and shadow zones. Second, extrapolation around caustics provides real and complex rays initial guesses. Third, their optimisation is performed using an adaptive algorithm. This process provides wave arrival times, azimuths, apparent velocities and over-pressures at a set of stations. Algorithm efficiency and robustness are illustrated by numerical examples: the ground sonic boom of a slightly supersonic aircraft (Mach cut-off problem), explosion at a ground-based point source, and the sonic boom from a meteorite atmospheric entry. In this last case, a 2D model has been developed inspired by the well-documented Carancas meteorite. Finally, comparisons are performed with other numerical methods.