Dispersed Infrasound Signals in the "Zone of Silence"
Abstract
During the last few years the use of seismo-acoustic recordings have become increasingly important; however, infrasound analysis methods lag behind seismic methods. The current paper discusses infrasonic signals in the so called 'Zone of Silence', at a distance up to 300 km from the source. During controlled source experiments in 2006 and 2007, tropospheric, stratospheric and thermospheric signals were recorded at a suite of temporary infrasound arrays; some of the tropospheric arrivals exhibit dispersion. The most common types of infrasonic signals observed during our studies beyond 76 km are stratospheric. These signals are not predicted by atmospheric modeling (raytracing and PE calculations) using the Naval Research Laboratory Ground to Space (G2S) model. The G2S model does not explain the observed tropospheric arrivals. Meteorological data from balloon launched rawinsondes obtained in the path of the propagating signals are able to predict the tropospheric propagation if the data closest to the detonation time is used. In a previous research study in the China Sea, a suite of dispersed infrasound signals were successfully interpreted as propagating in a low velocity waveguide. We also observed dispersed signals from an explosion at White Sands Missile Range recorded at TXIAR at a distance of 546 km. The signals exhibit dispersion between 0.2-1 Hz, and can be successfully modeled as propagating in a low velocity layer 1.2 km thick. However, dispersed signals recorded in Nevada suggest propagation in a waveguide consisting of a single low velocity layer is too simplistic. Effects due to lateral changes in effective sound speed, topography, turbulence and multiple layering can significantly affect the dispersion.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.S11B1734N
- Keywords:
-
- 7299 General or miscellaneous