Impact of GIM uncertainties on the single-frequency PPP over the Brazilian region

The vertical total electron content (VTEC) is one of the main quantities to describe the state of the ionosphere. To dispose this information is important to mass market Global Navigation Satellite System (GNSS) users to correct the ionospheric delay for positioning. The VTEC values and the corresponding standard deviations are routinely provided in the so-called Global Ionosphere Maps (GIM), with time intervals of 2, 1 and 0.25 hours on regular grids with 2.5º resolution in latitude and 5º resolution in longitude. To determine the ionospheric corrections from the GIMs for positioning applications, a quadratic interpolation is typically applied to the VTEC grid values which generally does not take into account the VTEC uncertainties. In this context, the impact of the use of the VTEC standard deviation is assessed in the positioning domain, considering the GIMs of two different analysis centers. The impact of the VTEC uncertainties is analyzed by means of single-frequency precise point positioning (PPP), applied to four Brazilian GNSS stations in different regions, considering four scenarios: geomagnetic storm, low solar flux and high solar flux (equinox and solstice). The use of the VTEC uncertainties values provided a significant improvement coinciding with high solar flux, especially for stations in regions under the most intense ionospheric effect, with mean rates of improvements up to 47%.