An Assessment of Ionospheric Effects on the GPS User

Paul S. Jorgensen

Abstract:	The single frequency, CIA code GPS user employs a rather simple analytic model of the ionospheric delay of the L1 GPS navigation signal. It is recognized that the model is an approximation and that its use will only partially remove ionospheric effects from the user's navigation solution. To perform an assessment of the residual effects of the ionosphere on navigation accuracy, this paper turns the problem around and uses the ionosphere model in a way that was not originally intended. Let's assume the model represents truth and a hypothetical user does not attempt to correct for its effects. With this approach, we have a means for obtaining various statistics of ionospheric effects on a world-wide, 24-hour basis. The paper presents results for both horizontal and vertical navigation errors as well as for time transfer errors. Time transfer results are given both for when time transfer is part of a three-dimensional navigation solution and for time transfer at a known location. Some of the results presented in this paper might appear to be quite surprising. The user position errors are low relative to the magnitude of the ionospheric delays. Furthermore, the horizontal errors are only about 1/6 of the vertical. These low errors are at the expense of the time transfer part of the navigation solution. From a known location, time transfer errors are much lower for two reasons: 1) There is no error amplification due to "geometric dilution of precision," and 2) We can limit ourselves to using high-elevation angle satellites.
Published in:	Proceedings of the 1989 National Technical Meeting of The Institute of Navigation January 23 - 26, 1989 San Mateo, CA
Pages:	43 - 46
Cite this article:	Jorgensen, Paul S., "An Assessment of Ionospheric Effects on the GPS User," Proceedings of the 1989 National Technical Meeting of The Institute of Navigation, San Mateo, CA, January 1989, pp. 43-46.
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