Infrasonics is the study of sound below the range of human hearing. These low-frequency sounds are produced by a variety of geophysical processes including earthquakes, severe weather, volcanic activity, geomagnetic activity, ocean waves, avalanches, turbulence aloft, and meteors and by some man-made sources such as aircraft and explosions.
Infrasonic and near-infrasonic sound may provide advanced warning and monitoring of these extreme events.
We are engaged in the development and deployment of infrasonic instruments for detection and monitoring of low-frequency sound generated by several important anthropogenic and geophysical processes. A strong focus is on hazardous geophysical phenomena in order to improve basic knowledge and early warnings. We have demonstrated that avalanches in the Rocky Mountains can be detected and located using an infrasonic array on the plains near Boulder. Using a similar array, we demonstrated that tornadoes on the high plains can be detected several minutes before they touch down, thus demonstrating a valuable tool to provide advanced warning for residents in tornado-prone regions. We conduct theoretical studies of infrasonic source mechanisms in order to optimize systems for detection and identification. The object of one study is the correlation between infrasound, sprites, and other transient, luminescent phenomena associated with severe weather. Another study involves methods to reduce audible noise (such as along highways) using both active and passive techniques. We typically collaborate with other organizations within NOAA, other government agencies, universities, and foreign scientists. For example, we are participating in a cooperative study with Armenian scientists researching earthquake precursors, and the we have been requested to assist with the Nuclear Test Ban treaty monitoring system. We also collaborate with other research groups in field experiments, e.g., involving Radio Acoustic Sounding System (RASS) and Lidar. Potential research and development include: infrasound observations from Peacewing platforms, infrasound measurements of other planetary atmospheres, and ocean wave generated infrasound with a focus on tsunami detection.
- Frequently Asked Questions about Tornadoes
- Low-Frequency Atmospheric Acoustic Energy Associated with Vortices Produced by Thunderstorms A.J. Bedard, Monthy Weather Review, vol. 133, 241-263.
- Atmospheric Infrasound, A.J. Bedard Jr. and T. M. Georges, Physics Today, March 2000. (18M PDF)
- Infrasonic and Near Infrasonic Atmospheric Sounding and Imaging A.J. Bedard Jr. Proc. Progress in Electromagnetics Research Symposium, 13-17 July 1998, Nantes, France, 4th International Workshop on Radar Polarimetry (1998)
- Project MCAT (Mountain Induced Clear Air Turbulence): Background, Goals, Instrumentation and Methodologies A.J. Bedard Jr. and P. Neilley, Proc. 8th Conf. Mountain Meteorol., Flagstaff, AZ, Aug 3-7, 1998.
- Sources of Infrasonic Tornado Signatures
- Infrasonics Review Poster
- HARPO: A Versatile Three-Dimensional Hamiltonian Ray-tracing Program for Acoustic Waves in an Ocean with Irregular Bottom R. Michael Jones, Riley, J.P., Georges, T.M., U.S. Department of Commerce, October 1986.
- HARPA: A Versatile Three-Dimensional Hamiltonian Ray-tracing Program for Acoustic Waves in the Atmosphere Above Irregular Terrain R. Michael Jones, Riley, J.P., Georges, T.M., U.S. Department of Commerce, August 1986.
- Seismic Response of Infrasonic Microphones A.J. Bedard, Journal of Research of the National Bureau of Standards, C. Engineering and Instrumentation Vol. 75C, No. 1 January-March 1971.