VLBI Observations of Galileo Satellites Enable Inter-Technique Ties

The study presents comprehensive VLBI observations of Galileo navigation satellites conducted with the Australian AuScope VLBI array. The research addresses the growing interest in geodetic co-location in space and space ties, particularly in light of ESA's Genesis mission. The observations, using 12-m antennas equipped with VLBI Global Observing System (VGOS) instrumentation, targeted Galileo E1 and E6 signals. The study demonstrates the estimation of VLBI station coordinates from observations to navigation satellites, establishing inter-technique ties between VLBI and GNSS. The processing strategy included correlation, fringe fitting, precision assessment, and satellite tracking. The delay observables achieved precisions of a few picoseconds in the E1 band and several tens of picoseconds in the E6 band for 1-s integration times. However, unmodeled signals on the order of several hundred picoseconds were found in the residual delays. The estimated station coordinates agreed with a priori values at the metre level, while baseline lengths agreed at the sub-metre level. These results demonstrate the feasibility of large-scale VLBI observations to GNSS satellites and provide critical groundwork for future co-location satellite missions such as Genesis. Future research should focus on modeling the unmodeled signals to improve the precision of VLBI observations. The integration of VLBI and GNSS data has the potential to enhance our understanding of Earth's dynamics and improve the accuracy of geodetic measurements.

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