From: Los Alamos National Laboratory
Posted: Friday, February 14, 2003
A Los Alamos National Laboratory researcher is helping to provide an extra measure of confidence in an international array of listening posts that keep an ear out for clandestine nuclear weapons tests.
Doug ReVelle of Los Alamos' Atmospheric, Climate and Environmental Dynamics Group today presented calculations showing the number of false alarms in international monitoring stations that can be attributed to meteors. ReVelle presented his findings at the American Association for the Advancement of Science's annual meeting in Denver.
ReVelle and his Los Alamos colleagues operate a series of stations that listen for infrasonic signals - very low frequency sound waves that lie below the range of normal human hearing. The stations are part of an international monitoring system that is used to detect, among other things, rogue atomic tests. Such tests create infrasonic signals, and researchers can analyze data from the stations to pinpoint the location and even the magnitude of a clandestine blast.
But incoming meteors also create infrasonic signals. When a meteor enters the atmosphere and continues traveling through it, it creates a pressure wave - the infrasonic signal. The pressure wave is akin to a pressure wave created by an explosion. Because of this, ReVelle often discusses meteor size in terms of explosive yield: the larger the yield, the greater the diameter of the meteor.
Recently, ReVelle teamed up with researchers from Sandia National Laboratories, the University of Western Ontario, ET Space Systems and U.S. Space Command and looked at sound and light signatures from large meteors that had entered the atmosphere during the last eight years. >From these data, the researchers were able to more precisely calculate the size and energy of incoming meteors.
In addition, ReVelle was able to calculate the frequency of meteor encounters with the atmosphere. A meteor that's 100 feet in diameter - with the energy equivalency of a one-megaton explosion - enters the atmosphere about every 100 years. But smaller meteors enter more frequently.
ReVelle looked at the number of meteors in the one-kiloton energy range (or meteors just under 10 feet in diameter) to determine the number of false alarms that might be seen on international monitoring stations worldwide. Based on his calculations, ReVelle found that individual monitoring stations would see, on the average, about five meteor signals a year.
"This research will help give added confidence to the international monitoring system," ReVelle said.
Los Alamos National Laboratory is operated by the University of California for the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy and works in partnership with NNSA's Sandia and Lawrence Livermore national laboratories to support NNSA in its mission.
Los Alamos enhances global security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and national security concerns.
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