As we approach the peak of solar cycle 25, we observe increasing ionospheric and scintillation activity, which is negatively impacting the quality of GNSS measurements and presenting challenges in the positioning domain. Ionospheric refraction and diffraction introduce delays and distortions to the GNSS carrier phase measurements, leading to positioning errors that exceed the anticipated accuracies. These position errors can be a significant concern for users across the world who depend on precise GNSS positioning such as agriculture, offshore marine positioning, autonomous automotive positioning. To understand the direct impact on NovAtel receivers and its positioning engines, a comprehensive analysis was conducted. We take a closer look at what happened in 2023-2024 by characterizing the scintillation using the amplitude scintillation index (S4) values in an equatorial region. Additionally, the scintillation effect on the receivers through the analysis of CN0, lock-breaks, double differences and other indicators were characterized. With a substantial amount of data collected at 20° latitude, where high solar activity occurs due to the proximity to the equator, the positioning performance of RTK and PPP were analyzed. As an example, Figure 1 below displays 24 hours of data collected in February 2023, the scintillation period is easily noticeable from approximatively 57000 to 597000 seconds GPS where we observe CN0 variation of up to 18 dB-Hz over a period of 1 second while variations are less than 1 dB-Hz outside of the scintillation period. Figure 2 shows the spatial ionospheric decorrelation for a 25km baseline using a double difference between a base and a rover. Errors of over 6 meters are observed during the scintillation period. Figure 3 shows the PPP results compared to RTK during the scintillation period. While the PPP solution error did increase during the scintillation period, it remained below 10cm and easily outperformed the RTK solution. Figure 4 shows 3D graphs of S4 values as a function of UTC time for a 30-day period (August 2023).
Figure 1: CN0 for all GPS L1CA satellites
Figure 2: Double Difference ADR for all GPS L1CA satellites
Figure 3: RTK and PPP Position Error (Continuous)
Figure 4: S4 values for August 2023 during 24h UTC
