Another cool thing about GPS is that it helps up predict weather. http://en.wikipedia.org/wiki/GNSS_radio_occultation http://en.wikipedia.org/wiki/GNSS_radio_o

Another cool thing about GPS is that it helps up predict weather. http://en.wikipedia.org/wiki/GNSS_radio_occultation http://en.wikipedia.org/wiki/GNSS_radio_occultation Basically, a satellite in orbit (which already knows where it is) will measure the time delay to a GPS satellite as the line of sight skims the edge of the atmosphere. The ray path will be affected by the refractive index of the atmosphere, which depends on its humidity and temperature. This allows temperature and humidity to be calculated for a range of altitudes as the line of sight moves, and is remarkably accurate - so much so that other observations are calibrated against GPS measurements.