Ionospheric Time Delay Variations at an Equatorial Station During Low Solar Activity
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The greatest source of error in position estimate and precise time transfer using Global Positioning System (GPS) satellites is range delays, which degrade GPS signals as they propagate through the ionosphere. In order to improve the accuracy of GPS position fixing, it is important to have a good understanding of ionospheric time delay. In this paper, we have studied the diurnal and seasonal variations of ionospheric time delay of radio signals from GPS satellites and their dependence on solar flux (10.7 cm) index during low solar activity period (March 2008 to December 2009) over an equatorial station, Lagos, Nigeria (6.5°N, 3.4°E; magnetic latitude 3.03°S). It is found that diurnal variation of ionospheric time delay show maximum values around 14h00-16h00 LT during all the months considered. The study reveals that during low solar activity, the time delay values are high in equinox months, least during summer and moderate in winter. The correlation between average daytime peak ionospheric time delay and the solar F10.7 flux shows low positive correlation, with Correlation Coefficient of R = 0.31 for 2008 and R = 0.15 for 2009.
Ionospheric time delay , Navigation , GPS , Total electron content
Journal of Sci. Res. Dev, (14) 85 – 94