Ionospheric Corrections From GPS Data and RIBG

Michael H. Reilly and Malkiat Singh

Abstract:	We show that GPS data can be processed for improved ionospheric specification. Differential carrier plhase between Ll and L2 frequenciesis is analyzed by a model in which the combined effect of hardware biases and phase ambiguity terms is represented by a constant for each receiver-satellite pair, and the ionospheric contribution, proportional to slant total electron content TEC, along the path, is represented by the RIBG (Raytrace/ ICED, Bent, Gallagaher) model. RIBG is a detailed global, empirical, climatological ionospheric model of electron density, with height coverage from 80 km. up to the top of the ionosphere at the plasmapamse, which is combined with a full 3D ray trace propagation model. Discrete inverse theory (DIT) is used to fit the driving (input) parameters of the ionospheric model in RIBG to GPS receiver data. Validity is established by the ability of the RIBG model, updated by GPS data in this way, to predict independent measurements of: (1) vertical total electron content (TEC,) over the ocean out to substantial distances from a GPS receiver, often in excess of 1000 nmi., and (2) the detailed electron density vs. height profile (EDP). GPS-updated RIBG is also used to predict, with and without the conventional spherical shell approximation, measured TECs variations for the trajectories of individual GPS satellites. The conventional spherical shell approximation provides an obliquity factor for mapping TEC, into TEC,. GPS-updated RIBG, predicts the measured TEC, variations much more closely without the spherical shell approximation than with it, particularly at smaller elevation angles, with some reservation from weakness in the low latitude part of the ionospheric model. We conclude that our method enables larger validity ranges and latencies for ionospheric specification from a single GPS reference receiver, as compared to a method based on the spherical shell approximation. Therefore, it enables the use of GPS reference station networks with longer baselines and data latencies. Implications for improved GPS navigation accuracy are discussed.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	297 - 305
Cite this article:	Reilly, Michael H., Singh, Malkiat, "Ionospheric Corrections From GPS Data and RIBG," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 297-305.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In