Both at: Geodetic Research Laboratory, Department of Geodesy and Geomatics Engineering
University of New Brunswick, P.O. Box 4400, Fredericton, N.B. E3B 5A3 Canada
Phone: 1-506-453-4698, Fax: 1-506-453-4943, email: lang@unb.ca
The dispersive nature of the ionosphere makes it possible to measure its total electron content (TEC) using dual-frequency GPS observations collected by permanent networks of receivers. One such network is that of the International GPS Service for Geodynamics (IGS). We have used dual-frequency GPS pseudorange and carrier phase observations from stations in this network to derive TEC values.
In earlier studies, based on Faraday rotation data as 'ground-truth' - with which we compared the performance of the GPS Broadcast and International Reference Ionosphere 1990 (IRI90) models - we concluded that both for day-time and night-time periods the IRI90 model appeared to be more accurate than the Broadcast model. This conclusion is specific to low solar activity and mid-latitude conditions based on a limited set of data. In a more recent study, we used our precise GPS-derived TEC values - with hich we compared the IRI90 TEC predictions - and the results indicated an agreement with the earlier studies concerning the accuracy of the IRI90 TEC predictions.
During the presentation we will present a sensitivity analysis of our current ionospheric modelling technique. The technique involves an estimation of ionospheric parameters assuming a Gauss-Markov stochastic process using a Kalman-filter approach. We will investigate the impact of using different elevation cutoff angles, varying ionospheric shell heights on the TEC estimates as well as the satellite-receiver differential delays. A concept of taking the spatial and temporal variation of the ionospheric shell height during the estimation will also be introduced.
As we start 'climbing up' the new solar cycle, we will be facing increased solar activity which will become a major concern for the single-frequency GPS users. We will investigate the accuracy and practicability of using this improved ionospheric model to account for the ionospheric effect in surveying and precise positioning using single-frequency GPS receivers.
This page was compiled by Attila Komjathy and last updated
15 September 1997. If you have any questions, comments
please feel free to get in touch with me.
You
can reach me at: komjathy@ocean.colorado.edu