Interesting article about GPS stations - CORS.
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.
Read the complete note: http://www.physorg.com/news/2011-06-gps-stations-clandestine-nuclear.html
Thoughts