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.