Effects of Ionosphere on Differential GPS

Abstract

Electrons in the ionosphere delay the arrival of the wave radiated from the GPS satellites, which cause a substantial excess path. For differential GPS, the difference of the excess path at the both ends of the baseline makes one of significant error sources for higher accuracy in determining baseline vector. Such delay may be corrected directly by observing total electron content (TEC) or the critical plasma frequency (f_0F2) at the site as an alternate quantity. Temporal changes of the correlations between these values are examined using the data obtained by Radio Research Laboratory at Kokubunji, Tokyo. The results show that the correlation is rather high in the winter time than in the summer time. Rough estimates of the spatial change of the excess path are also made by using both f_0F2 and TEC. Simple calculations indicate about 4 cm differences in excess path for 10 km baseline, for both f_0F2 and TEC.