SatCom and SatNav: TEC and Scintillation

• The quality of communications can be disrupted if the Total Electron Content (TEC) is too high, or if there is scintillation.
• Position resolution provided by Satellite Navigation systems such as GPS (and Galileo) can be degraded by high TEC (the signal is refracted and the extra path length causing timing errors) and by scintillation (the receiver can loose lock).
• There are additional problems related to satellite based augmentation systems (SBAS) such as WAAS, EGNOS, etc. At mid-latitudes, gradients in TEC can be quite large during geomagnetic storms and the SBAS cannot accommodate them either in accurately measuring the gradients (the spatial density of reference receivers is too small) or in updating the ionospheric correction model (the data rate is inadequate). The problem is aggrevated if reference stations have difficulties contacting sufficent spacecraft when gathering the data needed to calculate the correction matrix.

The map on the upper left shows the Total Electon Content derived from GPS observables (produced by JPL); the map on the upper right shows where scintillation recently occurred, derived from GPS phase fluctuations (data supplied by CLS and processed by UCL-MSSL). The lower left plot shows the latest satellite environment data and the map on the lower right shows auroral activity estimated from POES data (both plots produced by NOAA/SEC). Disturbances in the satellite environment can result in geomagnetic storms.