Accuracy of ionospheric models used in GNSS and SBAS: methodology and analysis

Abstract

© 2015, Springer-Verlag Berlin Heidelberg. The characterization of the accuracy of ionospheric models currently used in global navigation satellite systems (GNSSs) is a long-standing issue. The characterization remains a challenging problem owing to the lack of sufficiently accurate slant ionospheric determinations to be used as a reference. The present study proposes a methodology based on the comparison of the predictions of any ionospheric model with actual unambiguous carrier-phase measurements from a global distribution of permanent receivers. The differences are separated as hardware delays (a receiver constant plus a satellite constant) per day. The present study was conducted for the entire year of 2014, i.e. during the last solar cycle maximum. The ionospheric models assessed are the operational models broadcast by the global positioning system (GPS) and Galileo constellations, the satellite-based augmentation system (SBAS) (i.e. European Geostationary Navigation Overlay System (EGNOS) and wide area augmentation system (WAAS)), a number of post-process global ionospheric maps (GIMs) from different International GNSS Service (IGS) analysis centres (ACs) and, finally, a more sophisticated GIM computed by the research group of Astronomy and GEomatics (gAGE). Ionospheric models based on GNSS data and represented on a grid (IGS GIMs or SBAS) correct about 85 % of the total slant ionospheric delay, whereas the models broadcasted in the navigation messages of GPS and Galileo only account for about 70 %. Our gAGE GIM is shown to correct 95 % of the delay. The proposed methodology appears to be a useful tool to improve current ionospheric models.Postprint (author's final draft

The Impacts of the Ionospheric Observable and Mathematical Model on the Global Ionosphere Model

“…For the undifferenced ambiguity-fixed carrier-phase ionospheric observable in this paper, the ionospheric bias is built from the undifferenced wide-lane and ionosphere-free ambiguities, which have been fixed in double difference mode [31].…”

“…After assessing the accuracy of the ionospheric observable, the most accurate ionospheric observable can be used to assess the accuracy of the global ionosphere model with a similar test as in [31]. Assuming that the FL4 observable has the best accuracy, the RMS value for each epoch at every station can be calculated for the GIM…”

Consistency of seven different GNSS global ionospheric mapping techniques during one solar cycle

“…Assessments based on independent measurements of VTEC and STEC variation have provided a fair ranking and optimal weights for combination (see introduction and references in [22]). Moreover additional recent works are focused on GIM assessment from vessels, [27], at mid and low latitude GNSS receivers, [1], and looking the apparent stability of associated Differential Code Biases but not assuring an independent assessment, [32].…”

Carrier phase bias estimation of geometry-free linear combination of GNSS signals for ionospheric TEC modeling

“…As a result, the obtained ionospheric maps are characterized by a low spatial resolution of several degrees and temporal resolution of 5-120 min. The widely used International GNSS Service (IGS) global model has a spatial resolution of 5.0° × 2.5° and temporal resolution of 2 h. The most recent studies show that the absolute TEC accuracy is rather low and amounts to 4-5 TECU (Hernandez-Pajares et al 2017;Rovira-Garcia et al 2016). Due to the very dynamic changes of the ionosphere, taking place not only during adverse solar activity events and magnetic storms, the accuracy and resolution offered by the current global and regional models are often not satisfactory.…”

“…This is due to the important influence of the ionospheric delays on determining carrier phase ambiguities. Therefore, the development of high-accuracy models with higher spatial and temporal resolution is required to support carrier phase ambiguity resolution (Wielgosz et al 2005;Charoenkalunyuta and Satirapod 2014;Rovira-Garcia et al 2016).…”