Inframap Propagation Modeling Enhancements and the Study of Recent Bolide Events

Enhancements to the propagation modeling capabilities of the InfraMAP analysis tool kit are being developed in several areas. InfraMAP (Infrasound Modeling of Atmospheric Propagation) consists of three infrasound propagation models (3-D ray trace, normal mode, and parabolic equation), two atmospheric characterizations (HWM and MSISE), a global topography database, and user interfaces for model execution and data visualization. InfraMAP has been delivered to the research and development test bed and is currently being utilized by Comprehensive Nuclear-Test-Ban Treaty researchers and analysts. Three specific types of InfraMAP enhancements are addressed here. First, a low-frequency absorption model has been integrated for use by both rayand parabolic-equation (PE) propagation analyses. The absorption model predicts both classical (translation, diffusion) and relaxation (rotation, vibration) losses. Absorption is calculated from temperature, pressure, and atmospheric gas densities, which are determined using the environmental model MSISE. Second, a waveform synthesis capability has been integrated into the ray model. Eigenray solutions for a specific source-receiver scenario are used to synthesize a time-based waveform. A user-defined source waveform is convolved with weighted impulse functions at the eigenray arrival times. The impulse weighting is based upon a calculated absorption loss along each ray path. Finally, improved environmental variability modeling capabilities are being pursued to model the propagation variability induced by the environment. A sample from the Naval Research Laboratory atmospheric statistics database has been investigated for use in improving predictions of propagation variability. Propagation modeling studies have been performed for several recent bolide events, including the 1997 El Paso, Texas, bolide, the 2000 Acapulco bolide, the 2000 Yukon bolide and the 2001 Pacific bolide. Predicted absorption curves are compared to the spectra of observed waveforms. Nominal source localizations are computed from measured station azimuths. Enhanced localizations that correct for predicted azimuth deviation are also calculated for comparison. The dependence of eigenray arrival times on source height is shown to be a viable discriminator for source height estimation.