Abstract
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.
Highlights
The use of global navigation satellite system (GNSS) receivers is nowadays a well-established technique for positioning, navigation and timing on satellites in low earth orbit (LEO)
A better than 70% or, at least, 10 total electron content (TEC) units (TECU) correction is achieved for 87% of all observations in a year of high (2014) solar activity and 98% in a year of low (2017) solar activity
The results confirm that the effective ionization level Az of Galileo provides a suitable measure of total electron content for spaceborne receivers even though the ionospheric coefficients in the Galileo navigation message are optimized for use in terrestrial applications
Summary
The use of GNSS receivers is nowadays a well-established technique for positioning, navigation and timing on satellites in low earth orbit (LEO). At representative altitudes of 400–1400 km, these satellites are still located in the terrestrial service volume. The signal strength and visibility conditions are generally similar to those of terrestrial users and enable similar real-time navigation performances as well as geodetic-grade precise orbit determination in postprocessing (Montenbruck 2017). The orbital height of LEO satellites is typically at or above the ionospheric electron density maximum. Single-frequency receivers that are widely used for
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