A new way to detect secret nuclear tests: GPS

"GPS might at first seem like an unlikely source for nuclear test detection." Actually, it makes total sense. So much sense that the creators of GPS put sensors in the satellites to do this...

"GPS satellites carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor), that form a major portion of the United States Nuclear Detonation Detection System" http://en.wikipedia.org/wiki/Global_Positioning_System

This is a cool application of GPS radio occultation. For a simple overview, see:

http://www.atmo.arizona.edu/~kursinsk/GPS_RO_overview.htm

The same idea has recently been used to improve weather forecasts for a few years now (http://en.wikipedia.org/wiki/GPS_meteorology).

Differences in atmospheric gas density affect the propagation speed of the GPS radio signal. Peering thru the edge of the atmosphere at the constellation of GPS transmitters allows you to get a bunch of density/temperature profiles in a way that's immune to some instrumental artifacts of other instruments.

One of the inventors of the idea formed a company to cooperatively launch small satellites to do these retrievals:

http://geooptics.com/?page_id=35

If the data is accurate enough to detect a kiloton blast deep underground, what about conventional weapons on the surface? Could this be used to detect and track the use conventional explosives deep inside the territory of oppressive regimes?

Somehow I don't think this is the main sticking point preventing the US from ratifying the nuclear test ban treaty, as the article seems to suggest.