On the use of ionospheric scintillation indices as input to receiver tracking models Original Research Article

Ionospheric scintillation has its highest occurrence in equatorial and auroral regions (including northerly parts of Europe), and in the polar caps. Several research groups, including the Institute of Engineering Surveying and Space Geodesy (IESSG), at the University of Nottingham and the Insitute of Integrated Information Systems (I3S), at the University of Leeds, have been involved with ionospheric scintillation research and its impact on users of Global Navigation Satellite Systems (GNSS). Such effects may be severe, from degradation of measurement accuracy to complete loss of lock on the satellite signal. The main motivation of this paper is to exploit further a comprehensive archive of scintillation data gathered by the IESSG during the last high of the solar cycle, in order to assess the probability of GNSS receiver tracking failures occurring due to ionospheric scintillation. This archive contains GPS ionospheric scintillation data gathered simultaneously with four GSV4004 receivers (GPS Silicon Valley) in the UK and Norway, between June 2001 and December 2003, at geographic latitudes varying from 53 °N to 71 °N. However, the scintillation data that forms this archive is given by the indices S4 and σϕ (in particular the latter’s 60 s version, herein termed Phi60), which are only average values measured at the input of the receiver Phase Locked Loop (PLL). As such they do not provide sufficient information regarding the instantaneous values of phase and amplitude fluctuations that will affect the GNSS receiver performance. Although these indices can give an indication of forthcoming problems, receiver tracking models must also be considered in order to accurately model the influence of scintillation on receiver performance and on positioning accuracy. It is the tracking error at the output of the PLL that determines the accuracy of the range measurements which the receiver uses to compute position. This paper presents a strategy devised to enable the combination of a high-quality database of scintillation indices and high rate GNSS phase and amplitude data with state-of-the-art receiver tracking models in order to study receiver tracking performance under scintillation conditions. The experiments described in this paper demonstrate that scintillation indices such as those archived by the IESSG can be successfully used to compute the receiver tracking error variance using these models.