The ionosphere is characterized by dynamic changes, so for precise GNSS positioning it is required to provide accurate ionosphere model to support carrier phase ambiguity resolution. Determination of ionospheric delay id based on GNSS data processing from global or regional ground permanent networks, e.g. IGS, EPN. The improvements in ionosphere modeling is mainly related with the growing number of available GNSS systems (and satellites) as well as reference stations within dense GBAS networks. Nowadays the majority of the ionosphere models are based on carrier phase-smoothed pseudorange data, which presents low accuracy and requires strong smoothing of the results. The ionospheric delay obtained from smoothed pseudoranges has accuracy of about few TECU (Total Electron Content Unit), that correspond to a few decimeter accuracy of a delay. For this accuracy, it is reasonable to use spherical harmonics expansion for TEC parameterization in their global and regional solutions (Schaer, 1999; Hernández-Pajares et al., 2009; Schmidt et al., 2011). As a result, the obtained ionosphere maps are characterized by low spatial resolution of few degrees and temporal resolution of 5 do 120 minutes. Broadly used IGS model has spatial resolution of 5.0 x 2.5 degrees and temporal resolution of 2 hours, with an estimated accuracy of about 4 TEC (Hernández-Pajares et al., 2009; Hernández-Pajares et al., 2011). The development of high accuracy models with higher spatial and temporal resolution is required (Wielgosz et al., 2005). In last few years, a number of research papers about the ionosphere modeling from GNNS data were publish in high-quality scientific journals (Krypiak – Gregorczyk et al., 2013; Schmidt et al., 2011). The published results show that GNSS technique has still great potential if it comes to the ionosphere modeling. This is especially true in case of research aiming at the use of un-differenced (raw) carrier phase data and new GNSS signals (Hernández-Pajares et al., 2011; Schmidt et al., 2011).
The interest in ionosphere-related studies by our group is a logical consequence of cooperation with the University of Warmia and Mazury in Olsztyn (Polnad) and the Technical University of Catalonia (Spain) in ESA founded projects: PIOM-FIPP, HORION and ATOMIT-WARTK. Please read sub-chapters for details.
Hernández-Pajarez M., Juan J. M., Sanz J., Orus R., Garcia-Rigo A., Feltens J., Komjathy A., Schaer S. and Krankowski A., (2009): “The IGS VTEC maps: a reliable source of ionospheric information since 1998”, Journal of Geodesy, 83, No. 3–4, 263–275. DOI: 10.1007/s00190-008-0266-1
Hernandez-Pajares M., Juan J.M., Sanz J., Aragon-Angel A., Garcia-Rigo A., Salazar D., Escudero M., (2011): “The ionosphere: effects, GPS modeling and the benefits for space geodetic techniques”, Journal of Geodesy, 85(12), 887-907
Krypiak-Gregorczyk A., Wielgosz P., Gosciewski D., Paziewski J., (2013): “Validation of approximation techniques for local total electron content mapping”, Acta Geodynamica et Geomaterialia, v. 10, No. 3(171)
Schaer S., (1999): “Mapping and Predicting the Earth’s Ionosphere Using the Global Positioning System”, Ph.D. Thesis, Astronomical Institute, University of Berne
Schmidt M., Dettmering D., Moßmer M., Wang Y. and Zhang J., (2011): “Comparison of spherical harmonic and B spline models for the vertical total electron content”, Radio Science 46, RS0D11
Wielgosz P., Kashani I., Grejner-Brzezinska D.A., (2005): “Analysis of Long-Range Network RTK during Severe Ionospheric Storm”, Journal of Geodesy, Vol. 79, No. 9, pp. 524-531