ASSESSMENT OF TWO METHODS TO PROVIDE IONOSPHERIC RANGE ERROR CORRECTIONS FOR SINGLE-FREQUENCY GPS USERS
Attila Komjathy and Richard B. Langley
Both at: Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering
University of New Brunswick, Fredericton, N.B. E3B 5A3 Canada
Department of Radio Engineering, Czech Technical University
Prague, 166 27 Czech Republic
One of the major error sources in GPS positioning is ionospheric refraction which causes signal propagation delays. The disturbing influences of the temporally and spatially varying ionization of the ionosphere have great impact on satellite geodesy, especially on GPS. To correct data from a single-frequency GPS receiver for the ionospheric effect, it is possible to use empirical models. In this research, we investigated the GPS single-frequency Broadcast [Klobuchar, 1986] and the International Reference Ionosphere (IRI90) [Bilitza, 1990] models. The GPS single-frequency Broadcast model is available to GPS users as part of the navigation message. The IRI90 model is a standard ionospheric model developed by the International Union of Radio Science (URSI) and the Committee on Space Research (COSPAR). After Newby  investigated the IRI86 model's performance, we decided to include the new IRI90 model in our ionospheric research. We have used Faraday rotation data as 'ground-truth' with which we compared the vertical ionospheric range error corrections predicted by the Broadcast and IRI90 models. Some of the results shown here have been presented earlier [Komjathy et al., 1995].
Based on the comparison between the Broadcast and IRI90 models, we can conclude that both for day-time and night-time periods the IRI90 model appears to be more accurate than the Broadcast model. This conclusion is specific to low solar activity, and mid-latitude conditions. This investigation needs to be extended for medium and high solar activity periods and for low and high latitude regions of the earth. We plan on including other ionospheric models in our future investigations. We also wish to test model accuracies and efficiencies in processing static and kinematic GPS data.
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