Wide‐Area, Carrier‐Phase Ambiguity Resolution Using a Tomographic Model of the Ionosphere

A method for resolving GPS carrier‐phase ambiguities exactly at hundreds of kilometers from the nearest reference site has been tested under a variety of operating conditions, with help from a computed tomography model of the ionosphere. The objective is decimeter‐level (root mean square) wide area kinematic positioning in real time using broadcast orbits, and subdecimeter‐level positioning using precise orbits. This work is relevant to surveying and navigation, as well as to newer real‐time uses of GPS, such as monitoring of atmospheric water vapor. The paper shows how this objective could be achieved using GPS data from a wide area network to obtain a regional ionospheric model. Information from the model would then be transmitted to users so they could apply precise ionospheric corrections to their data at the approximately known locations of their rovers. Test results are summarized, including detailed results of one test involving a large‐area network and an active ionosphere.