GNSS Signal Monitoring

The ability to measure and monitor GNSS signal quality is critical to assessing GNSS system usability and performance. GNSS receiver technology relies on signals broadcast from satellites orbiting 20,000 km above the earth at a frequency of approximately -163 dBW or about the strength of a single Christmas tree bulb. This makes GNSS signals susceptible to interference from many sources.

The impact of increased ionospheric activity on GNSS operations can be particularly problematic. One source of ionospheric activity is Solar Maximum, a phenomenon that occurs approximately every 11 years, where the sun enters a period of increased activity. During this period, solar flares and Coronal Mass Ejections (CMEs) and subsequent atmospheric storms, disrupt the ionosphere which in turn distorts the satellite signals. Distorted GNSS signals can degrade position accuracy and measurement quality. In severe cases, the GNSS system might not be able to generate a positioning solution due to the lack of valid GNSS signals for computation.

In most automated systems or guidance applications, position solution accuracy is often of secondary importance when compared to integrity monitoring of the receiver output. It is critical for these systems to know when a computed position is corrupt, based on the raw measurement it received, so that it can be discarded from the solution.

Good awareness of conditions allows “workarounds” and rescheduling for certain applications. At a minimum, it ensures critical post-analysis of attempted work during the periods that were affected.

NovAtel’s GNSS Ionospheric Scintillation and TEC Monitor (GISTM) receiver tracks local anomalies that will affect GNSS signals. The receiver provides a quantitative measure of the reliability of the GNSS signals being tracked.