According to an article published in the Bulletin of Atomic Scientists, a GPS can be used to detect underground nuclear tests, GPS radio waves must pass from transmitters on satellites above the planet down to ground-based receivers. Time is an essential part of GPS and the presence or absence of particles in the atmosphere may speed up GPS radio signals or slow them down and this can be used to pinpoint nuclear tests.
In May 2009 North Korea exploded a nuclear bomb approximately a kilometer underground. But the explosion disturbed the ionosphere in a way that could be detected in GPS signals at 11 receivers in the region. The shockwave from the explosion spread out from the test site including high into the ionosphere. GPS signals have always been especially sensitive to atmospheric disturbances.
When the bomb test occurred in 2009, the authors were examining the problem of ionospheric disturbances affecting GPS. They gathered data from 11 GPS receivers in the region and found that the data showed a sudden spike in atmospheric electron density just after the underground test. They calculated that within 25 minutes, the shockwave had traveled 225 miles to the nearest GPS station and by the end of the first hour, the disturbance had reached all 11 stations. Based on the timing of the shockwave at the different receiver locations, the authors were able to trace the origin of the explosion back to P’unggye, in agreement with the seismic data for the event.
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