CALIBRA: Mitigating the impact of ionospheric scintillation on Precise Point Positioning in Brazil

The current increase in solar activity occurs at a time when our reliance on high-precision GNSS applications has reached unprecedented proportions. The perturbations caused in the ionosphere by such solar activity pose a major threat to these applications, in particular in equatorial regions such as Brazil where high exposure to solar-induced disturbances comes with a high reliance on precise GNSS applications in a number of key areas such as in the oil and gas industry. Mitigating the impact of severe ionosphere disturbance on high-precision positioning is the main goal of the FP7 CALIBRA project, which first results are discussed in this paper. We focus on the impact of scintillations, one of the most forthcoming disturbances, on real time precise point positioning (PPP). A simple and effective mitigation approach is discussed and shown to significantly increase the resilience of PPP applications to scintillations. INTRODUCTION GNSS has become essential to governmental and industrial sectors in support of activities such as precision agriculture, offshore operations, land management, construction, mining, as well as safety-critical operations, including those related to maritime, land and air transportation. The perturbations caused in the ionosphere by the current increasing solar activity, corresponding to the impending maximum of cycle 24, pose a major threat to these applications, in particular in equatorial regions where high exposure to solar-induced disturbances comes together with high reliance on high-precision GNSS. Brazil is one of the most affected countries. In particular, ionospheric scintillation is a daily issue impacting both the availability and accuracy of high-precision GNSSbased positioning techniques, such as Real-TimeKinematic (RTK) and Precise Point Positioning (PPP). Mitigating the impact of severe scintillation on highprecision positioning is the main goal of CALIBRA, a project funded by the European Commission in the framework of the FP7-GALILEO-2011-GSA activity. In this paper, we present the first results of the CALIBRA project, with as main focus the assessment of the impact of scintillation on Precise Point Positioning (PPP) and its mitigation. The remainder of this paper is organized as follows. First the context, scope and main objectives of the CALIBRA project are described. Next, we discuss the on-going monitoring of ionospheric scintillation in the region of interest, endeavored in the previous CIGALA project, and the resulting climatology results that are instrumental to assess the threat. Then, we zoom on the impact of scintillation on PPP, exploiting data collected during strong scintillation events. Finally, we discuss simple and effective mitigations at positioning algorithm level. THE FP7 CALIBRA PROJECT CALIBRA (Countering GNSS high Accuracy applications Limitations due to Ionospheric disturbances in BRAzil), a project funded under the Seventh Framework Program (FP7) by the European GNSS Agency (GSA) and coordinated by the Nottingham Geospatial Institute (NGI) at the University of Nottingham, deals with these ionospheric disturbances and their effect on GNSS high accuracy techniques. CALIBRA’s partners are the Centre for Atmospheric Research (CAR) at the University of Nova Gorica (UNG) in Slovenia, the Upper Atmospheric Physics group of Istituto Nazionale di Geofisica e Vulcanologia (INGV) in Italy, Septentrio Satellite Navigation NV (SSN) in Belgium, Sao Paulo State University (UNESP) and ConsultGEL (CSG) in Brazil. CALIBRA builds on the outcomes of the CIGALA project where it was demonstrated that signal tracking under ionospheric scintillation can be effectively mitigated by new algorithms and tracking loop configuration within the receiver signal tracking engine [14]. This is illustrated in Figure 1, which show the achieved loss-of-lock probability as a function of S4 (amplitude scintillation index) and user configurable loop bandwidth. The improved tracking robustness achieved in CIGALA, results in increased availability of the code and phase observables and, consequently, of the position solution (PVT) during moderate to strong scintillation. Figure 1 Tracking level mitigation of ionospheric