Ionospheric Scintillation Effects on GPS Carrier Phase Positioning Accuracy at Auroral and Sub-auroral Latitudes

Abstract

Ionospheric scintillation may present significant effects on GPS, mainly in equatorial and auroral regions, and during times of high solar flux. In the auroral regions scintillation occurrence mostly relates to geomagnetic activity and can affect GNSS users even at sub-auroral (and potentially mid-latitude) regions, with impact ranging from degradation of accuracy to loss of signal tracking. Recent work at Nottingham investigated the impact of ionospheric scintillation and Total Electron Content (TEC) gradients on GNSS users, through a network of four GPS Ionospheric Scintillation Monitors set up in the UK and Norway. Statistical analyses of the scintillation and TEC data, aiming to characterise ionospheric scintillation over Northern Europe, were also carried out. Critically to GNSS users these studies covered, in particular, aspects of availability and integrity, through the assessment of occurrence of loss of lock on GPS satellites due to high scintillation levels. However, accuracy aspects have also been investigated, through the analysis of standalone GPS, DGPS, EGNOS aided DGPS and carrier phase errors, which have been correlated with observed scintillation levels and geomagnetic indices. Horizontal errors in GPS C/A code point-positioning were seen to correlate to enhancement in the background TEC observed during times of occurrence of high scintillation. DGPS positioning accuracy was seen to be affected by TEC gradients occurring at auroral and sub-auroral latitudes, especially under enhanced geomagnetic activity. Missing corrections in the EGNOS ionospheric grid during periods of occurrence of high phase scintillation suggested an inability of the EGNOS reference stations to track one or both of the GPS signals of some satellites. In this paper the main focus is on carrier phase positioning experiments, which revealed an increase in the measurement noise and positioning accuracy degradation significantly correlated with the occurrence of high phase scintillation.