Ionospheric Delays for Simulation of GPS Users in Near Earth's Surface Navigation

Haywood Satz

Abstract:	A mathematical model of Global Positioning System (GPS) signal-ionosphericdelay in terms of User position, GPS position, and electron distribution has been developed. The Ionosphere was partitioned by concentric spherical surfaces to create layers of uniform charge density, and total ionospheric delay was modeled as a density path-integral. An algorithm was designed to compute the delays of the ionospheric model. That algorithm accepts input data defining electron charge distribution vs. altitude, and computes path length traversed, by the received signal, in each layer. The path-integral was computed numerically as a sum of incremental length-density products corresponding with the ionospheric layer partitions. Application of the developed model (and its algorithm implementation) was made to determine how much ionospheric delay would be encountered in a scientific mission of a spaceborne GPS receiver, and whether it was worthwhile making dual-frequency measurement compensation of those ionospheric delay errors. Effectiveness of compensation was measured, by computing delays for various User orbit altitudes and elevation angles, and by comparing those delays with the error due to compensation noise. The Appendix contains the development of the ionospheric delay model based on the numerical evaluation of a density path-integral. Path length through each layer was computed with a quadratic root formula for the path increment. Analytic solutions of the path integral were obtained by selecting certain ionospheric density distributions which enabled closed- form-integral delay evaluations. Numerical solutions were compared with analytic solutions to verify the model design and computation accuracy.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	835 - 841
Cite this article:	Satz, Haywood, "Ionospheric Delays for Simulation of GPS Users in Near Earth's Surface Navigation," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 835-841.
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