Abstract
The Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System that is currently under development. The Galileo HAS will start providing satellite orbit and clock corrections (i.e. non-dispersive effects) and soon it will also correct dispersive effects such as inter-frequency biases and, in its full capability, ionospheric delay. We analyse here an ionospheric correction system based on the fast precise point positioning (Fast-PPP) and its potential application to the Galileo HAS. The aim of this contribution is to present some recent upgrades to the Fast-PPP model, with the emphasis on the model geometry and the data used. The results show the benefits of integer ambiguity resolution to obtain unambiguous carrier phase measurements as input to compute the Fast-PPP model. Seven permanent stations are used to assess the errors of the Fast-PPP ionospheric corrections, with baseline distances ranging from 100 to 1000 km from the reference receivers used to compute the Fast-PPP corrections. The 99% of the GPS and Galileo errors in well-sounded areas and in mid-latitude stations are below one total electron content unit. In addition, large errors are bounded by the error prediction of the Fast-PPP model, in the form of the variance of the estimation of the ionospheric corrections. Therefore, we conclude that Fast-PPP is able to provide ionospheric corrections with the required ionospheric accuracy, and realistic confidence bounds, for the Galileo HAS.
Highlights
The Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System (GNSS)
The Fast-precise point positioning (PPP) corrections are computed by a central processing facility (CPF), which retrieves data from permanent stations belonging to the networks of the International GNSS Service (IGS) (Beutler et al 1999) and the Rede Brasileira de Monitoramento Continuo (RBMC), code and carrier phase measurements at multiple frequencies and from multiple constellations
Assuming that the ionospheric pierce point (IPP) is surrounded by four ionospheric grid points (IGPs) located in the same layer at a given time, the user interpolates the vertical TEC (VTEC) at the four IGPs using the linear distances x and y: VIPP (1 − y)Va + yVb where Va and Vb are computed as
Summary
The Galileo High Accuracy Service (HAS) is a new capability of the European Global Navigation Satellite System (GNSS). Multi-frequency receivers shorten the time required to obtain a decimetre level of accuracy (i.e. the convergence time), as it is required in the phase 2 of Galileo HAS This is because ionospheric corrections help the navigation filter to separate (i.e. decorrelate) the carrier phase ambiguities from the other parameters estimated: coordinates, time offsets and troposphere. Far away from the reference stations, the GIVEIs of the ionospheric model should be high enough that the ionospheric correction does not help nor bias the navigation solution The aim of this contribution is to present some recent upgrades to the Fast-PPP ionospheric model tailored to the Galileo HAS (phase 2), which include the multi-constellation capability and to confirm the performance obtained in the past with GPS data [see Rovira-Garcia et al (2016a) and RoviraGarcia et al (2020)]. The manuscript finalizes presenting a summary of the main findings and conclusions
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