Estimating the effects of an ellipsoidal earth and topography on infrasonic propagation

Abstract

Infrasonic signals often propagate significant horizontal distances so that predictions obtained using a flat ground approximation can introduce inaccuracies. Simulations of propagation in an atmospheric layer around a spherical globe have shown non-negligible deviations from flat ground predictions for both arrival locations and propagation times. Simulation predictions for flat-ground and spherical earth models will be discussed and the additional challenges of implementing a non-spherical globe model and the inclusion of topography will be discussed using the approximation of geometric acoustics. A non-spherical globe model, such as the WGS84 ellipsoid, is found to produce range dependence in the propagation medium, even in the case that a stratified local atmosphere is assumed. Further, although scattering and diffraction effects are not included in the geometric limit, variations in the ground surface level can be included in ray path computation to more accurately model propagation of infrasound. Propagation effects will be detailed in the case of a tropospheric waveguides for which interaction with the ground surface is significant as well as the case that source and receiver locations have differences in elevation.