[G05-3] Positioning applications

[G05-3-01] Higher Order Ionospheric modelling campaigns for precise GNSS applications

^○Tomasz Hadas¹, Jan Kaplon¹, Anna Krypiak-Gregorczyk², Manuel Hernandez-Pajares³, Pawel Wielgosz², Alberto Garcia-Rigo³, Jacek Paziewski², Kamil Kazmierski¹, Jaroslaw Bosy¹, Krzysztof Sosnica¹, Dawid Kwasniak³, Marcin Pucilowski⁴, Robert Szyszko⁴, Raul Orus Perez⁵ (1.Wroclaw University of Environmental and Life Sciences, Wroclaw, Poland, 2.University of Warmia and Mazury, Olsztyn, Poland, 3.Universitat Politecnica de Catalunya, Barcelona, Spain, 4.Leica Geosystems Poland, Warsaw, Poland, 5.European Space Research and Technology Centre, Noordwijk, Netherlands)

The first order ionospheric term (I1) is the main contributor to the ionospheric delay of GNSS observations, compared with the less than 0.1% corresponding to the higher order ionospheric terms. However, higher order ionospheric effects (I2+) are one of the main limiting factors in very precise GNSS processing, for applications where millimetre accuracy is demanded. The consortium of LGP, WUELS, UWM and UPC deals with higher order ionospheric mitigation under the HORION (Higher Order Ionospheric modelling campaigns for precise GNSS applications) project, supported by the European Space Agency. This HORION project is focused on the development of the HORION-PL web service for mitigation of higher order ionospheric terms, thus improving precise GNSS processing.
Within this project we also investigated the impact of I2+ on troposphere delay estimation, long-range relative positioning and autonomous positioning. We selected three networks (global, Polish and Brazilian) and three test period (each one week long, reflecting solar minimum conditions, solar maximum conditions and geomagnetic storm). We also estimated GPS and GLONASS orbit and clock products, that were further used in GNSS processing. We performed each processing in two variants 1) with original RINEX files, and 2) with I2+ corrected RINEX files, to assess the impact of I2+ effects on the results.
The initial analysis of I2+ impact on orbit modelling showed the following RMS of residuals: 1.1 mm, 3.7 mm and 3.3 mm for radial, along and out-of-plane component respectively. For troposphere, the average ZTD difference was -0.06 mm with 0.20 mm of standard deviation, with the extreme ZTD differences reaching 3.4 mm and -4.4 mm. ZTD differences obtained in Brazilian network fluctuates following daily I2+ correction oscillations. In Poland this effect is smaller, due to shorter baselines and lower ionosphere activity.