GPS ionospheric tomography: A comparison with the IRI-2001 model over South Korea

The International Reference Ionosphere model 2001 (IRI-2001) is one of the most comprehensive empirical models of the ionosphere and has been widely used to estimate the electron density profiles in the altitude ranging from about 60 to 2000 km and the total electron content (TEC) at any given location, time and date, which reflect smooth-average global ionospheric behaviors. However, whether it provides normal actual estimations in the ionosphere over some regions should be tested with real observation data. In this paper, the threedimensional ionospheric electron density profiles over South Korea in 2003 are obtained using the ionospheric tomography reconstruction technique with the permanent Korean GPS Network (KGN) data, and its validity is further verified by another independent ionosonde data. The GPS ionospheric reconstruction results are used to compare then results obtained with the IRI-2001 model in South Korea in terms of NmF2 and TEC. The monthly averaged diurnal values of these key parameters in January, April, July and October 2003 are considered to represent the winter, spring, summer and autumn seasons, respectively. Compared with the GPS reconstruction results, averaged monthly NmF2 medians from the IRI-2001 are overestimated in daytime and underestimated in nighttime for all seasons, but the deviation magnitudes in autumn and winter are smaller than in spring and summer. In addition, averaged monthly TEC medians from the IRI-2001 are overestimated in daytime in winter, but almost always underestimated in other seasons.