Determination of Position Errors for Single-Frequency

Patricia H. Doherty, Matthew C. Smitham, Susan H. Delay, Gregory J. Bishop

Abstract:	Mathematical analysis was performed to investigate navigational position errors caused by inaccuracies in the standard Ionospheric Correction Algorithm (ICA) used by all single-frequency GPS receivers. The ICA, developed in the 1970’s, was designed to correct for 50% of the delay on pseudoranges introduced by the ionosphere. Therefore, in many cases, a residual delay error remains on each pseudorange. Errors, like these, were computed by comparing the ICA estimate with measured and modeled ionospheric values. These errors were then propagated through the solution process to determine the navigation position error. The most significant impact occurs when a gradient exists in the pseudorange errors, with least importance on their magnitude. Three dimension position errors of 10, 20, and 40 meters are possible in equatorial latitudes for solar minimum, moderate and maximum conditions, respectively. The largest errors are generally confined to equatorial regions where sharp ionospheric gradients, caused by the equatorial anomaly, frequently occur. Preliminary and successful validation of this method has been performed by comparing these results with differences in positional data recorded by co-located single and dual-frequency GPS receivers on Ascension Island.
Published in:	Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999) June 27 - 30, 1999 Royal Sonesta Hotel Cambridge, MA
Pages:	355 - 362
Cite this article:	Doherty, Patricia H., Smitham, Matthew C., Delay, Susan H., Bishop, Gregory J., "Determination of Position Errors for Single-Frequency," Proceedings of the 55th Annual Meeting of The Institute of Navigation (1999), Cambridge, MA, June 1999, pp. 355-362.
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