A New, Improved Ionospheric Correction Algorithm for Single Frequency GPS Receivers

Robert E. Daniel Jr., Lincoln D. Brown, and Robert W. Simon

Abstract:	A new ionospheric time delay model for single frequency GPS users is being developed by Computational Physics, Inc. (CPI) under an SBIR Phase II contract from the Geophysics Directorate of Phillips Laboratory (PL/GP). The primary goal of the development is to reduce the RMS residual error of the algorithm f?om the current 50% to 30% or less. The improvement is likely to be even better in the low latitude region, where the current algorithm does not attempt to capture typical ionospheric morphology. The new algorithm is being designed to have minimal impact on existing GPS receivers and GPS operations. It will take advantage of the revolution in computing technology to store a more complex and accurate ionospheric model in the receiver and to drive it with a small set of parameters encoded in the GPS navigational message. It will also take advantage of advances in ionospheric modeling techniques to reduce both modeling error - resulting from inaccurate modeling of ionospheric Total Electron Content (TEC) - and mapping error - resulting from inaccurate estimation of slant TEC from modeled vertical TEC The development effort is composed of four stages: (I) production of a global model of TEC (and other ionospheric parameters) based on the Global Theoretical Ionospheric Model (GTIM) of PL/GP, (2) development of an accurate vertical-to-slant TEC mapping tinction for use with that model, (3) implementation of the model in a form suitable for incorporation into single frequency receivers, and (4) validation of the algorithm using dual frequency data obtained by PL/GP. Implementation of the model (Stage 3) will be carried out in coordination with the GPS Joint Program Office (JPO) and with GPS receiver manufacturers to insure minimal impact on GPS operations and maximal availability to single frequency users.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	635 - 640
Cite this article:	Daniel, Robert E., Jr., Brown, Lincoln D., Simon, Robert W., "A New, Improved Ionospheric Correction Algorithm for Single Frequency GPS Receivers," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 635-640.
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