Near-Real-Time Maps of Vertical Total Electron Content (VTEC) in the Ionosphere over South America, Central America and the Caribbean for 2020

Abstract

Regional ionosphere maps (RIMs) in near real-time, using data from about 220 GNSS sites of the IBGE (Brazil), IGN (Argentina), UNAVCO (USA), SGM (Uruguay), IGS (BKG, Germany) and other agencies. Multi-frequency and multi-GNSS observations (GPS, GLONASS, Galileo and BeiDou) are employed. The vertical total electron content (VTEC) is modeled in a solar-fixed reference frame using a Green's function for a spherical spline in tension. The time spacing of their vertices is 15 minutes, conforming with the epochs of the VTEC maps. To convert line-of-sight TEC into vertical TEC, a modified single-layer model mapping function approximating the JPL extended slab model mapping function is adopted. The mapping function is evaluated at geodetic satellite elevation angles. For the computation of the ionospheric pierce points, a spherical layer with a radius of 6821 km is assumed, implying geocentric, not geodetic latitudes. Instrumental biases with respect to each involved GNSS code observable are estimated with the same time spacing of the TEC maps (i.e. every 15 minutes). They are modeled with one set of bias parameters for each satellite-station link, for each pair of bands available. NO ZERO-MEAN CONDITION IS APPLIED.