Ionospheric Effects on Low-Latitude Space Based Augmentation Systems

P. H. Doherty, T. Dehel, J. A. Klobuchar, S. H. Delay, S. Datta-Barua, E. R. de Paula and F. S. Rodrigues

Abstract:	The FAA´s Wide Area Augmentation System (WAAS) was primarily developed for use in the mid-latitude CONtiguous United States (CONUS), where the ionosphere is well studied and well behaved. In the low- latitude regions, the magnitudes of the absolute range delay values are much higher, and the equatorial anomaly produces large spatial gradients over latitude. In the CONUS region, scintillation effects are very rare, but strong amplitude fading and phase scintillation effects occur regularly in the equatorial anomaly regions. Associated with the irregularities that produce scintillation effects are large plasma depletions in ionospheric range delay that may severely limit Space Based Augmentation System (SBAS) Precision Approach (PA) availability in those regions during those times. The FAA´s WAAS system will likely be the first of several SBAS systems to operate in various parts of the world. SBAS technology is also being developed for operational use in Japan (MTSAT) and Europe (EGNOS). The FAA National Satellite Test Bed (NSTB) program, a prototype WAAS, is currently involved in joint test efforts with Chile, Singapore and Brazil for the purpose of determining the feasibility, limitations and benefits of SBAS technology in those countries. In data that the NSTB has collected and analyzed from these sites, scintillation and equatorial anomaly effects are apparent. In this paper, we will present the ionospheric phenomena that may challenge SBAS operation at low latitudes. This presentation will include statistical summaries of long- term scintillation activity in Brazil. In addition, we present data describing the effects of scintillation on GEO WAAS messages and on a WAAS dual-frequency receiver operating in Rio de Janeiro, Brazil since October 2001. This data will provide insight into low latitude ionospheric effects on Precision Approach capability in this most challenging ionospheric environment.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1321 - 1329
Cite this article:	Doherty, P. H., Dehel, T., Klobuchar, J. A., Delay, S. H., Datta-Barua, S., de Paula, E. R., Rodrigues, F. S., "Ionospheric Effects on Low-Latitude Space Based Augmentation Systems," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1321-1329.
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