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.