You may be carrying in your pocket the
technology to detect clandestine nuclear tests.
New research into GPS
disturbances high up in Earth's ionosphere reveals that sometimes the
“noise” in the GPS signals are secret underground nuclear tests.
Not only that, but tests with archived GPS data not only detect the nukes, but can be
used to track the ionospheric noise back to its source.
“That noise became our signal,”
said Dorota Grejner-Brzezinska, professor of Geodetic and
Geoinformation Engineering at Ohio State University. She was
addressing reporters Tuesday at a press conference at the American
Geophysical Union meeting in San Francisco. The research, she said,
started out as an attempt to identify and remove noise from the GPS
data.
Like earthquakes, underground nuclear
blasts send pulses of acoustic energy up through the earth that
momentarily disturb the ionosphere. Those disturbances propagate outward
through the ionosphere like waves from a stone thrown into a pond. As
the ionospheric disturbance passes between a GPS satellite and a GPS
receiver on the ground, there is a noticeable blip error in the data.
Add together lots of other such errors from the same wave passing
between multiple receivers and satellites, and you get a lot of very
specific data that points back to a the source.
“It's very similar to seismological
detection of an epicenter (of an earthquake),” explained Jihye
Park, a post-doctoral researcher at Ohio State University. In fact
the same methods can be used as those employed by seismologists, she
said.
They applied their technique to
archived data and found clear signals of US nuclear tests from the
1990s as well as underground detonations in North Korea.
The new technique was verified by yet
another unlikely blast detection tool: The Very Large Array (VLA) in
New Mexico.
“We have to do the same thing:
Correct for ionospheric distortion,” said radio astronomer Joseph
Helmboldt of the Naval Research Laboratory. The VLA is made up of
lots of smaller radio telescopes working together, and since each one
looks though a slightly different patch of the ionosphere, any
disturbances have to be accounted for and corrected, he explained.
“We paired with the group from Ohio
State to see if we could see these tests,” Helmboldt said. They
used archived radio data from a 1992 nuclear test in Nevada and, sure
enough, saw the fast-moving signal crossing the sky over the VLA.
Despite being a lot more compact than a global GPS array, the radio
telescope did help confirm what the GPS folks were seeing, he said.
Although the GPS/radio telescope method
is not an officially approved method for monitoring for secret
nuclear tests, it does provide an additional method to verify what is
detected by seismic networks, said Grejner-Brzezinska.
“Both methods are quite effective,”
said Grejner-Brzezinska. And GPS, like seismic data, is available in
real time, so can be put to work quickly – which is always good
when people are nervous and want to know who has got a nuke.
