Ionospheric Analysis in the Equatorial Region: Impact on GNSS Performances

M. Cueto, A. Cezon, S. Pineda and E. Sardon

Abstract:	At equatorial latitudes the ionospheric activity can become a limitation on GNSS augmentation systems. In order to analyze the equatorial ionospheric effects on satellite navigation systems, a 6-years dual frequency GPS dataset from a maximum of 42 IGS stations was processed. Maximum ionospheric TEC values and gradients, as well as rate of TEC (RoT) values were analyzed as a function of time, elevation and geomagnetic latitude. The mapping function distortion and the ionospheric scintillations behaviour were also studied in order to complete the analysis. Residual positioning errors may persist in regions of steep TEC gradients. At low latitudes (near the equatorial anomaly) and during periods of solar maximum an enhancement of large-scale TEC gradients is observed. In this paper, maximum temporal and spatial TEC gradients have been calculated and analyzed using IONEX and GILION TEC values. Ionospheric irregularities can be detected and characterized by calculating the rate of TEC. In this paper RoT values were computed by differencing the phase measurements over 60 seconds after cycle slips removing. Mean, RMS, maximum and minimum RoT values were analyzed for different hours, months, years, elevations and geomagnetic latitudes in order to characterize and quantify the ionospheric irregularities. Possible multipath effects will be taken into account when analyzing the results. At very low latitudes the sTEC computation error due to the mapping function could become significant. An analysis of the relation between GILION vertical and slant TEC values near the geomagnetic equator has been developed. GILION tool is based on a Kalman filter and allows us to estimate inter-frequency hardware biases and TEC values at each epoch. Finally, the impact of the ionospheric effects on GNSS performance is discussed in this paper. In particular, an analysis of the SBAS performances for Centre-South America is performed taking into account the ionospheric conditions in the region as output of the previous analysis. The objective of this paper is not only to go deeper in the ionospheric knowledge in the CAR/SAM (Centre-South America) region using a great amount of real data, but to extrapolate the conclusions of these studies to preliminary analyze the impact on future SBAS systems (like the Solución de Aumentación para Caribe, Centro y Sur América, SACCSA).
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2324 - 2336
Cite this article:	Cueto, M., Cezon, A., Pineda, S., Sardon, E., "Ionospheric Analysis in the Equatorial Region: Impact on GNSS Performances," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2324-2336.
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