This article focuses on the new generation of Very Long Baseline
Interferometry (VLBI), the VLBI Global Observing System (VGOS), and
measurements carried out during CONT17 campaign. It uses broadband
technology that increases both the number and precision of observations.
These characteristics make VGOS a suitable tool for studying the
atmosphere. This study focuses on the effects of the ionosphere on VGOS
signals using a model that incorporates and extends ideas originally
published in Hobiger et al. (2006). Our investigation revealed that the
differential Total Electron Content (dTEC) data product calculated with
the VGOS post-processing software revealed a sign error in the inferred
dTEC values. Fortunately, this error does not change the final values of
the phase and group delay. Therefore, this study was a way to identify
this problem within the VGOS data. After diagnosing and solving this
problem, the Hobiger et al. (2006) model was modified such that instead
of considering a single unknown for the latitude gradient of the
ionosphere, a time series of latitude gradients were taken into account.
For comparison purposes, time series of Vertical Total Electron Content
(VTEC) at each station during CONT17 campaign were constructed from
Global Ionosphere Map (GIM) data. In this way, it is shown that the
final accuracy of estimating VTEC at each station using VGOS data was
between 1.0 and 5.8 TEC Units (TECU).