Investigation of strongly ducted infrasonic dispersion using a vertical eigenfunction expansion of the Helmholtz equation in a modal broad band acoustic propagation code

Abstract

This study investigates an infrasound propagation model created by the National Center for Physical Acoustics (NCPA) which is applied to atmospheric data with a strong temperature inversion in the lower atmosphere. This temperature inversion is believed to be the primary cause of a dispersed infrasonic signal recorded by an infrasound sensor array located on the Southern California coast in August, 2012. The received signal is characterized by initial low frequency content followed by a high frequency content tail. It is shown the NCPA model is hindered by limited atmospheric data and no ground truth for the source function which generated the received signal. The results of the NCPA model are shown to not reproduce the recorded signal and provide inconclusive evidence for infrasonic dispersion.