Real-time Ionospheric Tomography Using Terrestrial GPS Sensors

Andrew J. Hansen

Abstract:	We present a novel technique for estimating the four-dimensional state of the ionosphere based on tomography using a terrestrial based reference network. The two key innovations in this technique are real-time operation and the ability to ensure integrity of the resulting estimate. The technique has been tailored into an ionospheric correction model for our wide area differential GPS correction system which is running on the FAA’s National Satellite Test Bed (NSTB). The discussion focuses on the state space formulation of the underdetermined inverse problem inherent in tomography. The state space model, in particular the observation matrix, is cast using a spectral basis which we construct specifically to treat the ill-conditioned observation geometry of the instantaneous terrestrial measurements. The state space model is implemented as a real-time filter on live observations to form electron density reconstructions. The electron density estimates are used to correct the ionospheric error in the GPS navigation solution and generate appropriate confidence intervals on single frequency observations from independent monitor stations. The performance of the differential correction is assessed using the triplet of Wide Area Augmentation System (WAAS) system metrics which measure accuracy, integrity, and availability. The criteria for success under these metrics are commensurate with safety of life applications and as such are extremely stringent.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	717 - 727
Cite this article:	Hansen, Andrew J., "Real-time Ionospheric Tomography Using Terrestrial GPS Sensors," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 717-727.
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