The coverage area of a regional ionosphere map is mainly determined by the geometry of ground monitoring stations, which are used to receive GNSS signals for correction signal generation. With the small number of the ground stations in small area, the coverage becomes very small and the use of the ionosphere map is limited to the small area. We tested three interpolation methods to evaluate the extrapolation accuracy of the ionospheric delay corrections outside the coverage area. Simulated data set is used to compute the error statistics. Hourly and annual variations of the errors are analyzed. The biharmonic method yields the best accuracy and outperforms Klobuchar model provided from GPS broadcast message.

Keywords: GNSS, Ionospheric delay, Extrapolation