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Contact: James Rickman
jamesr{at}lanl.gov
505-665-9203
DOE/Los Alamos National Laboratory
February 14, 2003

Los Alamos researcher quantifies meteor false 
alarm rate for nuclear test monitoring system
=============================================

DENVER, Feb. 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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http://www.eurekalert.org/pub_releases/2003-02/danl-lar021203.php

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