Monitoring Ionospheric Scintillation Effects on Precise Positioning in the North America Region
GPS signals travel through the ionosphere, where the speed of the signal is sensitive to the total electron content of the ionosphere. Additionally, small-scale electron density variations cause the received signal to vary in both intensity and phase, a phenomenon called scintillation. This can affect the accuracy and availability of GPS services. While scintillation is commonly observed in polar and equatorial regions, during moderate to severe geomagnetic storms ionospheric irregularity and scintillation activity in the polar region expands to lower latitudes that include the contiguous United States (CONUS). The National Oceanic and Atmospheric Administration's Space Weather Prediction Center does not currently have a product to report scintillation occurrence and user impacts.
The rate of TEC index (ROTI) is a measurement that characterizes ionospheric irregularities. It can be obtained from standard GPS dual-frequency phase data collected using a geodetic type of GPS receiver. By processing GPS data from the ground-based network of Continuously Operating Reference Stations (CORS) covering the United States region including Alaska, we have produced ROTI maps to observe regional scintillation activities. Our analysis indicates that prominent ROTI and L1 phase scintillation are well correlated temporally in the polar region, where L1 amplitude scintillation is rare. We report a major mid-latitude scintillation event in the contiguous United States characterized by ROTI maps, using data collected during a space weather storm.
We performed a survey of GPS users which concluded that, besides the effect of amplitude (and phase) scintillation in the equatorial and low-latitude regions that could cause signal power fading, the precise positioning user base is very sensitive to the polar phase scintillation effects which might expand down to the CONUS region. We show that significant (more than an order of magnitude) positioning errors can occur under phase scintillation conditions and that these errors are well correlated with ROTI. We also demonstrate using ROTI maps to produce a nowcast product of ionospheric scintillation effects on precise positioning users.