Page 11 - April 2008

HIGH-ALTITUDE INFRASOUND CALIBRATION EXPERIMENTS
Eugene T. Herrin
Department of Geological Sciences, Southern Methodist University Dallas, Texas 75275
Henry E. Bass
Jamie Whitten National Center for Physical Acoustics, University of Mississippi
University, Mississippi 38677
Bill Andre
Radiance Technologies Huntsville, Alabama 35805
Robert L. Woodward
Incorporated Research Institutions for Seismology Washington, D.C. 20005
Douglas P. Drob
Space Science Division, Naval Research Laboratory Washington, D.C. 20375
Michael A. H. Hedlin
Institute of Geophysics and Planetary Physics, University of California, San Diego
La Jolla, California 92093
Milton A. Garcés
Infrasound Laboratory of the University of Hawaii Kailua-Kona Kailua-Kona, Hawaii 96740
Paul W. Golden
Department of Geological Sciences, Southern Methodist University Dallas, Texas 75275
David E. Norris
BBN Technologies Arlington, Virginia 22209
Catherine de Groot-Hedlin
Institute of Geophysics and Planetary Physics, University of California, San Diego
La Jolla, California 92093
Kristoffer T. Walker
Institute of Geophysics and Planetary Physics, University of California, San Diego
La Jolla, California 92093
Curt A. L. Szuberla
Geophysical Institute, University of Alaska Fairbanks Fairbanks, Alaska 99775
Rodney W. Whitaker
Los Alamos National Laboratory Los Alamos, New Mexico 87545
F. Douglas Shields
Jamie Whitten National Center for Physical Acoustics, University of Mississippi
University, Mississippi 38677
Introduction
Infrasound (acoustic signals below
the 20 Hz limit of human hearing) has
been known since the eruption of
Krakatoa in 1883. This event registered
on barometers around the world. In
1909, barometers also registered a
strong signal from the now-famous
Tunguska event. As illustrated by these
two cataclysmic events, infrasound
energy can travel reasonably unattenu-
ated for thousands of kilometers
through refractive ducts in the atmos-
phere. Recognizing the utility of this
energy as a tool for the remote study of atmospheric sources, and as a probe of the atmosphere, infrasound was commonly used to monitor atmospheric nuclear tests start- ing in the 1940’s. With the Limited Test-Ban Treaty that eliminated atmospheric nuclear testing and with the advent of satellite technology, infrasound research had declined dramatically by the early 1970's. The recent Comprehensive Nuclear Test-Ban Treaty (CTBT) that banned nuclear tests of all yields, in all environments, included the use of a worldwide network of infrasound receiving arrays. This has led to a re-birth of infrasound as a technology for monitoring the Earth’s atmosphere and
“An obstacle to refining our knowledge of infrasound propagation and improving source location techniques has been the lack of sources with known yield, location, and time.”
shallow crust for nuclear tests as well as other natural phenomena.
The re-birth and study of infra- sound has led to improvements in instrumentation such as microbarome- ters and has benefited from advances in digital signal processing and recent improvements in knowledge of the mid- dle- and upper-atmosphere. New infra- sound stations, such as those deployed as part of the CTBT, have led to dramat- ic increases in the quality and quantity of data available. However, the physics of global infrasound propagation is not
fully understood and significant challenges remain before better advantage of this wealth of new data can be taken. This has led to dynamic research programs in areas such as evaluation of signal propagation codes, atmospheric mod- els, development of infrasound as a remote sensing tool (e.g., earthquakes, volcanoes), and operational infrasound source location and characterization. An obstacle to refin- ing our knowledge of infrasound propagation and improv- ing source location techniques has been the lack of sources with known yield, location, and time.
To improve understanding of the most pressing research issues, a calibration experiment was organized
Infrasound Calibration Experiments 9