Investigation of the Effects of Fine-scale Atmospheric Inhomogeneities on Infrasound Propagation

Recent infrasound observations and related research work in long-range sound propagation indicate that fine-scale atmospheric inhomogeneities contribute to refraction, scattering, and related phenomena that can result in anomalous infrasonic arrivals. Gravity waves, in particular, have been shown through physics-based modeling to be responsible for infrasonic arrivals, at regional ranges, that are not predicted by standard modeling techniques. Atmospheric turbulence can also cause scattering of infrasound that produces arrivals in shadow zones at local ranges from ground based sources. We seek to improve understanding of the effects of gravity waves and other fine-scale atmospheric inhomogeneities, such as Kelvin-Helmholtz turbulent instability, on infrasound propagation. The approach is to build on recent advances in specifying the lower and middle atmosphere, state-of-the-art infrasound propagation calculation techniques, and existing stochastic models of gravity waves and turbulence. Atmospheric specification techniques are being developed that incorporate realistic models of gravity waves that are self-consistent with the background flow field and that include effects of altitude, latitude, longitude, and time-evolution over relevant scales. The research effort includes systematic evaluation of the relevant atmospheric phenomena, improved atmospheric specification, advancement of the state-of-the art of modeling the interactions between fine-scale atmospheric inhomogeneities and infrasound, and model validation studies using ground truth datasets, focusing on local and regional ranges. Anticipated results of the work include new modeling tools to improve capability to predict infrasound arrivals and features relevant to phase classification at local and regional ranges. 2008 Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies