Global ionospheric models in three dimensions from GPS measurements: Numerical simulation

A network of globally distributed dual frequency Global Position System (GPS) receivers is used to compute global maps of the vertical total electron content (VTEC) distribution of the ionosphere. A mapping function is used to convert the total elec tron content along the path of the signal into vertical total electron content, which can be represented by two dimensional Taylor s eries or spherical functions. This vertical variation cannot be recovered directly from GPS data measured with ground based receivers. The technique was tested with the launch of the GPS - MET mission on April 3, 1995. Combining the trans-ionospheric measurements from ground based receivers with the data collected in the GPS-MET experiment we attempt to model the electron content based on the global behaviour of the ionosphere. Using least square estimation we determine the unknown coefficients of the electron content model. The results suggest that, even without a global geometrical distribution, the space receiver is useful to model the mean high electron content variation.