Ionospheric tomography helps resolve GPS ambiguities on the fly at distances of hundreds of kilometers during increased geomagnetic activity

We describe a procedure for resolving ambiguities in real time with the help of very precise ionospheric corrections calculated tomographically using data from several reference stations that are part of a local area automatic control network. We report successful results during a period of high geomagnetic activity (Kp=6) in the region of the Pacific Northwest (in Washington and British Columbia), using a set of continuously operating IGS stations with separations of between 400 and 1000 km. While the data were collected before the test, our calculations carefully emulated those made in a real-time situation. All GPS receivers were dual-frequency. This is a proof-of-concept for the use of such a technique in the operation of large regional networks of automatic stations, capable of supporting sub-decimeter surveying and navigation in real time anywhere within their area