Effect of Ionospheric Activities on GNSS Positioning16 May 2022
Ionospheric activity can adversely affect the performance of GNSS receivers. Increased ionospheric activity is correlated with the following factors:
- Sunspot Activity – increased ionospheric activity linked with the 11-year solar cycle. Sunspot activity can be monitored by using a notification service such as spaceweather.com.
- Solar and Magnetic storms – cause an increase in the ionospheric activity.
- Geographic Location – highest activity along the geomagnetic equator and in auroral (polar) regions.
- Seasonal Variations – increased activity at the Vernal and Autumnal Equinoxes.
- Diurnal (Daily) Variations – maximum effects normally experienced post-local sunset hours until midnight.
While the ionospheric error is estimated and corrected for in GNSS positioning, at times of increased ionospheric activity adverse effects to tracking and positioning are expected.
The increase in ionospheric activity can have two effects:
- The most significant effect is scintillation, which is caused by small scale irregularities in the ionosphere caused by the solar activity. Scintillation effects GNSS signal tracking, causing fluctuations in the amplitude and phase of the carrier phase signal, introducing noise or causing loss of lock to the satellite. This can result in a reduced number of usable GNSS satellites and occasionally a reduction in the L-Band communications link strength, causing intermittent reception of the augmentation data.
Scintillation affects are normally seen in the evening within a period of 6 hours after local sunset along the geomagnetic equator and are not predictable.
- It can introduce large errors/biases (up to 15 meters) into single frequency position solutions including Differential GNSS. These effects are easily mitigated by dual frequency systems. TerraStar and Oceanix services are not affected by this, and it is recommended to use TerraStar-C PRO and Oceanix subscriptions in polar and equatorial regions.
The following are recommended to help mitigate the effects of increased ionospheric activity:
- Use as many additional GNSS constellations (GLONASS, BeiDou, Galileo) as possible to increase the number of observations available to the position solution.
- Use all available L-band beams to ensure that corrections can still be received if lock to one satellite is lost. With OEM6, users can choose to auto-assign beams to avoid reliance on a single manually selected beam. All OEM7 receivers simultaneously track all available L-band beams by default, so a user should be unaffected by a loss of data from a specific L-band satellite. Where available, IP correction delivery (NTRIP) should also be used.
Although these steps may mitigate the adverse effects of scintillation, in some extreme circumstances all GNSS and Lband signals may be impacted, resulting in total loss of GNSS positioning.
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