Tomographic modeling of GNSS ionospheric corrections: Assessment and real-time applications

M. Hernandez-Pajares, J. M. Juan, J. Sanz and O.L. Colombo

Abstract:	It has been demonstrated in previous work that the tomographic approach reduces significantly the mismodelling in the electron content determination with Global Navigation Satellite Systems like GPS. We present in this paper the results of an comprehensive study about the performance of a tomographic model of the ionosphere, computed from the L1 and L2 carrier phase data, in order to estimate undifferenced and double differenced ionospheric corrections. Firstly, previous work has shown that the comparison with the TOPEX-Poseidon altimeter TEC for more than 2.5 years of data, including Solar Maximum (June 1998 to 2001), presents errors of few TECU at mid and high latitudes for the post-processed TEC computed from GPS data, and 5-10 TECU in equatorial regions. The real-time TEC computed close to equatorial regions, using the ambiguities fixed in the ionospheric model, is better than those post-processed results. During four consecutive weeks in March-April 2001, under Solar Maximum conditions, including some days of high geomagnetic activity, the STEC errors are less than 5 TECU and about 1 TECU for double differenced STEC, with reference stations separated 1000 to 3000 km, and close to the southern Appleton anomaly. These results strongly suggest that these models can improve significantly both navigation and time transfer with single frequency receivers, even in equatorial regions. Secondly, the real-time doubledifferenced ionospheric corrections have been studied for six different scenarios at medium and high latitudes during 17 different days in 1999, 2000 and 2001, and including different ionospheric conditions, such as geomagnetic activity and Traveling Ionospheric Disturbances (TIDs). The results for the WADGPS-like scenarios indicate that the tomographic model is accurate enough (better than 0.25 TECU for the rover receivers) to solve on-the-fly the carrier phase ambiguities, at distances of hundreds of kilometers of the nearest reference receiver, allowing for example very precise navigation (errors below 10 cm), and real-time tropospheric determination within WADGPS networks.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	2507 - 2515
Cite this article:	Hernandez-Pajares, M., Juan, J. M., Sanz, J., Colombo, O.L., "Tomographic modeling of GNSS ionospheric corrections: Assessment and real-time applications," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 2507-2515.
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