Low-latitude GNSS ionospheric scintillation dependence on magnetic field orientation and impacts on positioning

Ionospheric scintillation often occurs in equatorial and low-latitudes regions between +/- 20 degrees geomagnetic latitude and impacts GNSS performance on geodetic applications. In equatorial and low latitude regions, scintillation on the GNSS signal occurs mainly due to small-scale irregularities inside plasma bubbles that are magnetic field-aligned structures. We derived the propagation angle between GNSS ray paths and magnetic field lines to quantify scintillation occurrences of multi-constellation GNSS signals in relation to magnetic field orientation. Precise point positioning (PPP) solutions are obtained to assess the field-aligned scintillation signal impacts on positioning. A case study based on observations in Hong Kong is conducted to characterize a typical low-latitude region near the northern equatorial anomaly crest. Measurements from multiple GNSS constellations, i.e., GPS, GLONASS, Galileo and BDS are used. Results suggest that the GNSS scintillation intensity is enhanced in the local southern sky within the azimuth range of 150 degrees-240 degrees with peak at similar to 180 degrees, where the signal paths closely align with the magnetic field lines. Analysis of the data show that up to five GPS satellites may have their signal paths aligned closely with magnetic field lines simultaneously. This can result in an increase in the kinematic PPP errors from several centimetres to tens of meters. The relationship between the scintillation occurrence and magnetic field orientation could be exploited in the future to mitigate scintillation effects on GNSS applications.