Deriving ionospheric total electron content by VLBI global observing system data analysis during the CONT17 campaign
Motlaghzadeh, Sanam; Alizadeh, M. Mahdi; Cappallo, Roger; Heinkelmann, Robert; Schuh, Harald
This article focuses on the new generation of geodetic very long baseline interferometry (VLBI), the VLBI global observing system (VGOS), and measurements carried out during the 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, https://doi.org/10.1029/2005RS003297). Our investigation revealed that the differential total electron content (dTEC) data product calculated with the VGOS post-processing software had a sign error that fortunately, does not change the final values of the phase and group delay. Therefore, this study was a way to identify this problem within the dTEC product. After diagnosing and solving this problem, the underlying 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 considered that enhanced the resulting vertical total electron content (VTEC) estimates. For evaluation purposes, time series of VTEC at each station during the CONT17 campaign were compared with VTEC obtained from the global navigation satellite system (GNSS). The final agreement between VGOS and GNSS was between 1.1 and 5.9 TEC units (TECU).
