Analysis Of The Interoperability Of The Gps And Galileo Ionosphere Models

The ionosphere is the part of the upper atmosphere that is kept partially ionized by ultraviolet light and X-rays from the Sun and influences radio propagation to distant places on the Earth. The effect of the ionosphere is important for any GNSS ranging system which has the signals pass through the Earth's atmosphere to a receiver on or near the Earth's surface. The amount of the ionospheric code delay and phase advance of the GNSS signals varies from a few meters to tens of meters depending on location, time within the day, and solar-geomagnetic conditions. Other than multipath, the ionosphere is the most significant error source for single-frequency GNSS users. In order to improve positioning accuracy and reliability, the effect of the ionosphere on single-frequency observations must be corrected by using a model. To mitigate the ionospheric effect, currently, the GPS and Galileo systems broadcast a set of coefficients for their ionosphere models, the Klobuchar model for GPS and NeQuick-G for Galileo, in their navigation messages. The main objective of the research described in this paper is evaluating the interoperability of the GPS and Galileo ionosphere models for GPS by analyzing the performance of the models in the positioning domain. For precisely analyzing the interoperability and to provide more knowledge of the GPS and Galileo ionosphere models, the analysis has been also conducted in the measurement domain. To see the spatial and temporal variations in the performance of the models, a data set with a total of 36 sample stations over two years, the year 2014 and the year 2015, has been used. Results determined via the conducted research indicate that the performance of the NeQuick-G model is better than that of the Klobuchar model for ionospheric quiet condition days. For disturbed conditions, based on eight ionospheric storm days during the same period, the Klobuchar model showed slightly better performance. We anticipate that the results and analysis of this research could serve as a sandbox for further improvement of ionosphere models for GNSS and their users.