NeQuick-G performance assessment for space applications

Other than traditional single-layer ionosphere models for global navigation satellite system (GNSS) receivers, the NeQuick-G model of Galileo provides a fully three-dimensional description of the electron density and obtains the ionospheric path delay by integration along the line of sight. While optimized for users on or near the surface of the earth, NeQuick-G can thus as well be used for ionospheric correction of single-frequency observations from spaceborne platforms. Based on slant and total electron content measurements obtained in the Swarm mission, the performance of NeQuick-G for users in low earth orbit is assessed for periods of high and low solar activity as well as different orientations of the orbital plane with respect to the sun and the region of high total electron content. A slant range correction performance of better than 70% is achieved in more than 85% of the examined epochs in good accord with the performance reported for terrestrial users. Likewise, the positioning errors can be notably reduced when applying the NeQuick-G corrections in single-frequency navigation solutions. For users at orbital altitudes, it is furthermore shown that vertical total electron predictions from NeQuick-G may be favorably combined with an elevation-dependent thick-layer mapping function to reduce the high computational effort associated with the integration of the electron density along the ray path for each tracked GNSS satellite.