Revisiting European VLBI Intensives for Rapid UT1-UTC Determination

Accurate, low-latency UT1–UTC estimates are essential for monitoring Earth’s highly variable rotation and for real-time applications ranging from GNSS to lunar and deep-space missions. One-hour VLBI Intensive sessions, typically conducted with two stations on long east–west baselines, have the primary goal of providing rapid UT1–UTC estimates. Due to the short session length and the limited network geometry, only a few geodetic parameters can be estimated, while all remaining Earth orientation parameters, as well as station and source coordinates, must be fixed to their a priori values. 

Previous simulation studies have shown that UT1-UTC sensitivity does not depend solely on the east-west extension and baseline length, but also on the orientation of the baseline, making, for example, equatorial baselines, despite their east-west geometry, suboptimal for determining UT1-UTC. Thus, renewed interest in establishing a European Intensive capability motivated the investigation of the potential for a regional VGOS Intensive network, including NYALE13N (Norway), RAEGSMAR (Portugal), and WETTZ13S (Germany). While earlier concepts for European Intensives did not mature operationally, the recently released improved error models for simulating the troposphere, which is the primary source of error in VLBI, provide a more realistic approximation of performance, as they reflect location- and time-dependent conditions. In this study, we simulate candidate Intensive configurations and quantify their potential for determining the highly variable parameter UT1-UTC through simulations.