Wednesday 24 August 2005

G7
1100-1230 hours

255
Ionospheric scintillation effects on GPS positioning accuracy at auroral and sub-auroral latitudes
Dodson, Alan¹, Aquino, Marcio¹, Souter, Jock¹, Moore, Terry¹
1 IESSG - Nottingham University, UK
Author email: alan.dodson@nottingham.ac.uk
Ionospheric scintillation may present significant effects in equatorial and auroral regions, especially 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. The IESSG has recently carried out work in this area, in a study that 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 were carried out, aiming to characterise ionospheric scintillation over Northern Europe. Critically to users the study 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 were also 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. This paper concentrates in this area, discussing results with implications on GNSS measurement and positioning accuracy. 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 high latitudes, especially under enhanced geomagnetic activity. Carrier phase positioning experiments revealed an increase in the measurement noise and positioning accuracy degradation significantly correlated with high phase scintillation. Missing corrections in the EGNOS ionospheric grid during periods of occurrence of high phase scintillation suggest an inability of the EGNOS reference stations to track one or both of the GPS signals of some satellites.

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