Modeling Low Latitude Ionospheric Dispersion

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

Abstract:	The low latitude ionosphere covers a large region straddling the geomagnetic equator and includes half the earth’s surface area and many geographic regions of economic, political, and military importance. The morphology of the low latitude ionosphere is complex and includes spatial and temporal variability on a wide range of scales. The present GPS single frequency ionospheric time delay algorithm does not capture this morphology. As a result of a Phase I SBIR study we have identified the necessary ingredients that an improved GPS ionospheric algorithm must incorporate if accurate ionospheric range corrections are to be available for single frequency users. The first ingredient necessary for an improved algorithm is better ionospheric climatology, especially for the low latitude region. We have adopted the approach used in the development of PIM, a parameterization of physics- based theoretical models that we developed under contract to Phillips Laboratory. The second ingredient is a better algorithm for conversion from vertical TEC to slant TEC in the low latitude region. The traditional method neglects horizontal gradients, which is invalid in the low latitude region throughout most of the day. The final ingredient is the availability of timely information about parameters that affect the ionosphere. For the low latitude ionosphere, this is primarily the diurnal pattern of vertical drifts that produce the equatorial anomaly. Near-real-time data on the daily variability of the low latitude drift pattern will probably become available in a few years. The improved algorithm that we are developing under Phase II of the SBIR contract will be capable of using that data.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	567 - 572
Cite this article:	Daniell, Robert E., Jr., Brown, Lincoln D., Simon, Robert W., "Modeling Low Latitude Ionospheric Dispersion," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 567-572.
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