NeQuick-G performance assessment for space applications

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.

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

“…equatorwards from the auroral oval. Solar energetic particles (E > 10 MeV protons), on the other hand, precipitate directly from the solar wind into the polar region (geomagnetic latitudes above ∼ 60 • ); however, the largest of those events are rare and typically occur only a few times per solar cycle (Neale et al, 2013). Energetic neutral atoms (1-1000 keV, principally within the 100 keV range; Orsini et al, 1994;Roelof, 1997;Goldstein and McComas, 2013) are produced via charge exchange when energetic ions interact with background neutral atoms such as Earth's geocorona.…”

“…By using an adequate mapping function, the vertical TEC, vTEC, can be obtained (e.g. Noja et al, 2013;Zhang et al, 2016;Montenbruck and Rodríguez, 2020;Jin et al, 2019). For ground-based receivers, it is often assumed that the pierce point of the ionosphere is at 350 km, and a thin, shell-like ionospheric model is used for obtaining vTEC.…”

NeQuick-G and Android Devices: A Compromise between Computational Burden and Accuracy

“…The code of this NeQuick-G implementation is available at https://www.gsc-europa.eu/support-to-developers/nequick-g-source-code and has been used in this work for studying the impact of the correction update rate. Finally, a C++ implementation of the model was developed by the authors of [ 23 ].…”

“…The main limitation to the usage of the NeQuick-G model is its computational load, which mainly is due to the numerical integration needed to compute the STEC. In particular, height-dependent electron density profiles above numerous foot points have to be evaluated, leading to a large computational load [ 23 ]. The effort required for running NeQuick-G has been estimated to be 60 times larger than that needed for the Klobuchar model [ 24 ].…”

“…The main limitation of the NeQuick-G model is its computational load [ 23 , 24 ]. This aspect is of foremost importance for smartphones, which have limited computational capabilities.…”