Performance Comparisons Between the Current and a New Prototype Single Frequency Ionospheric Correction Algorithm

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

Abstract:	We are developing a new ionospheric correction algorithm for single frequency GPS receivers under a Small Business Innovation Research (SBIR) contract with the Geophysics Directorate of the Air Force Phillips Laboratory. This algorithm was described at the 1996 ION-GPS meeting [Daniel et al., 19961. A proposed change in the Navigation Message was described at the ION National Technical Meeting [Shank and Daniell, 19971. We have developed a regional prototype of the new algorithm covering the low latitude ionosphere between 300Q-340QE longitude. The latitude region is approximately *44Q on either side of the geomagnetic equator. The emphasis in this paper is on performance comparisons between the new prototype algorithm and the current algorithm [Hobuchar, 1987; Spiker, 19961. The performance assessment was made using dual frequency data obtained from the International GPS Service for Geodynamics (IGS) Central Bureau at the Jet Propulsion Laboratory with additional processing by Phillips Laboratory and Boston College. Additional ionospheric data from the TOPEX dual frequency radar altimeter and provided by the Jet Propulsion Laboratory was also utilized. The TOPEX data was used to estimate the magnitude of the equatorial vertical drift. In actual operation, this information will be provided by Defense Meteorological Satellite Program (DMSP) data using an algorithm being developed by the Air Force Research Laboratory (AFRL), but this data was not immediately available so we used TOPEX data instead. Both the current Klobuchar algorithm and the proposed algorithm were used to predict the ionospheric range correction along the lines-of-sight to the GPS satellites observed by the IGS stations. The actual ionospheric range delay was determined from the dual frequency measurements and compared to the two algorithm predictions. Because of the limited latitude and longitude range of this prototype, we used only data from the IGS receiver at Fortaleza, Brazil. Because both the IGS network and the TOPEX satellite began operating after the last solar activity maximum, only solar moderate data was used.
Published in:	Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997) June 30 - 2, 1997 Albuquerque, NM
Pages:	101 - 106
Cite this article:	Daniel, Robert E., Jr., Brown, Lincoln D., Simon, Robert W., "Performance Comparisons Between the Current and a New Prototype Single Frequency Ionospheric Correction Algorithm," Proceedings of the 53rd Annual Meeting of The Institute of Navigation (1997), Albuquerque, NM, June 1997, pp. 101-106.
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