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GPS technology detects secret nuclear tests

Vienna, Austria: At the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) meeting, American researchers explained how GPS technology can detect illegal nuclear explosions.
Even underground nuclear tests leave their mark on the part of the upper atmosphere known as the ionosphere, the researchers discovered, when they examined GPS data recorded the same day as a North Korean nuclear test in 2009. Within minutes on that day, GPS stations in nearby countries registered a change in ionospheric electron density, as a bubble of disturbed particles spread out from the test site and across the planet.
“It is like the shockwave from the underground explosion caused the earth to ‘punch up’ into the atmosphere, creating another shockwave that pushed the air away from ground zero,” said Ralph von Frese, professor of earth sciences at Ohio State University and senior author on the study. Jihye Park, a doctoral student in geodetic science at the university presented the results of the study in a poster session at the CTBTO meeting in Vienna, Austria.
Park said that seismic detectors pick up shockwaves through land, and acoustic sensors monitor for shockwaves through water and the air for tests that happen above ground. Chemical sensors detect airborne radioactive gas and dust as definitive evidence of a nuclear explosion. However, these particles may be lacking if the explosion is contained deeply below ground. “GPS is a complement to these other methods, and can help confirm that a nuclear test has taken place – especially when the test was underground, so that its effect in the air is very subtle, and otherwise nearly impossible to detect,” she added.
Dorota Grejner-Brzezinska, a professor of geodetic science at Ohio State and Park’s advisor, said, “GPS signals must pass from transmitters on satellites high above the planet down to ground-based receivers. Air molecules – more specifically, the electrons and other charged particles in the ionosphere – interfere with the signal, generating position error. Part of our research concerns how to compensate for that vulnerability and make GPS work better. Jihye found a way to take that vulnerability and turn it into something useful.”
Park wrote computer algorithms that search GPS signals for patterns indicating a sudden fluctuation in atmospheric electron density in specific locations, which is what happens when a shockwave pushes a bubble of air through the atmosphere. As the GPS signal passes through the edge of the bubble, the change in electron density disturbs the signal in a noticeable way. Park utilised data collected from GPS receivers that the International GNSS Service (IGS) has planted around the globe for research purposes.
Collaborators on the study include Yu Morton, professor of electrical and computer engineering at Miami University in Oxford, Ohio, and Luis Gaya-Pique of CTBTO’s On-Site Inspection Division.
Source: OSU