Abstract
The ionosphere is one of the main factors affecting the accuracy of global navigation satellite systems (GNSS). It is a dispersive medium for radio signals, and for multi-frequency receivers, most of its effect can be removed. The problem is for the single-frequency devices, which must rely on a correction model. The motivation of this paper is the adoption of different ionospheric models in GPS/EGNOS (Global Positioning System/European Geostationary Navigation Overlay Service) positioning to mitigate the impact of geomagnetic storms. The aim of this article is to examine the accuracy of GPS/EGNOS single-frequency positioning. In all the examined solutions, GPS L1 data augmented with the EGNOS clock and ephemeris corrections were used in position calculation. The changes were only made to the ionospheric model. The examined scenarios are as follows: without any model (off), Klobuchar, NeQuick G, and EGNOS model. The analysed period is 6–12 September 2017, during which the last strong geomagnetic storm took place. In order to perform a reliable analysis, the study was conducted at three International GNSS Service (IGS) stations in different geographical latitudes, within the EGNOS APV-1 (Approach with Vertical Guidance) availability border. The obtained results prove that the EGNOS ionospheric model meets the aviation positioning accuracy criteria for the APV-1 approach during the studied geomagnetic storm. The EGNOS average horizontal positioning error of 0.75 m was on average almost two times lower than the other solutions. For vertical positioning, the EGNOS error of 0.93 m proved to be two times lower than those of the Klobuchar and NeQuick G models, while it was more than three times lower for the off solution.
Highlights
The electromagnetic wave propagation through the atmosphere has a significant impact on radio signals transmitted by satellites towards the Earth
Radio signals crossing the ionosphere suffer several ionospheric effects such as phase advance, group delay, refraction, absorption, Faraday rotation, or amplitude and phase scintillation. Most of those effects depend on the ionospheric total electron content (TEC), which is defined as the electron density in a cross-section of 1 m2, integrated along a slant path between two points; it is expressed in TEC units (TECU), where 1TECU equals 1016 electrons/m2
The article presents the results of GPS/EGNOS positioning using different ionosphere models at three International GNSS Service (IGS) stations located at different latitudes during a strong ionospheric storm in September 2017
Summary
There are various approaches to mitigate ionospheric effects on GNSS positioning They depend on desirable accuracy and on the availability of signal frequencies. It was reported by Jacobsen and Andalsvik [8] that for RTK (Real Time Kinematic) positioning the error caused by the impact of geomagnetic storm was in the range of cm–dm level. Monitoring Stations (RIMS) and uses the data to elaborate clock corrections for each GPS satellite in view, elaborate ephemeris corrections to improve the accuracy of spacecraft orbital positions, and elaborate a model for ionospheric errors over the EGNOS service area in order to compensate for ionospheric perturbations [18]. The motivation of this paper is the examination of the accuracy of GPS/EGNOS single-frequency positioning with the adoption of different ionospheric models to mitigate the impact of geomagnetic storm in the European coverage area.
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