IONOSPHERIC CALIBRATION OF SINGLE-FREQUENCY VLBI AND GPS OBSERVATIONSUSING DUAL GPS DATA

The ionospheric effect is one of the main sources of error in Very Lon g Baseline Interferometry (VLBI) and Global Positioning System (GPS) h igh precision geodesy. Although the use of two frequencies allows the estimation of this effect, in some cases dual observations are not pos sible due to the available equipment or the type of observation. This paper presents the ionospheric calibration of single frequency VLBI an d GPS observations based on the ionospheric electron content estimated from dual frequency GPS data. The ionospheric delays obtained with th is procedure and the VLBI baseline length results have been compared w ith those obtained with dual frequency data. For the European geodetic VLBI baselines, both solutions agree at the 3-5 parts in 10(-9) level . The noise introduced by the GPS-based calibration is in the order of 3 cm for the VLBI observables and of 10 cm for the GPS observables.