Probing a southern hemisphere VLBI Intensive baseline configuration for UT1 determination

Area of Science:

• Geodesy and Astrometry
• Earth Rotation and Geodynamics
• Radio Astronomy Techniques

Background:

• Accurate measurement of the deviation of Universal Time from atomic time (UT1-UTC) is crucial for geodetic applications, requiring rapid observation and analysis.
• Existing Very Long Baseline Interferometry (VLBI) Intensive sessions, while effective, are limited to the northern hemisphere, potentially introducing unknown systematic errors.
• The need for global geodetic data and the inclusion of southern observatories motivated the development of the Southern Intensive (SI) program.

Purpose of the Study:

• To assess the competitiveness and accuracy of the Southern Intensive (SI) VLBI program in measuring UT1-UTC.
• To evaluate the potential systematic errors arising from northern hemisphere-dominated VLBI geometries.
• To demonstrate the capability of southern hemisphere VLBI observations for rapid UT1-UTC provision.

Main Methods:

• Conducted 53 SI sessions using three southern hemisphere VLBI antennas (Hartebeesthoek, Tasmania, Western Australia) during 2020-2021.
• Analyzed UT1-UTC results from SI sessions and compared them with conventional northern hemisphere Intensive sessions and the 14C04 analysis series.
• Assessed the impact of using a single baseline (HtHb) on the quality of UT1-UTC results.

Main Results:

• SI program demonstrated competitiveness with routine Intensive sessions in terms of operations and UT1-UTC accuracy.
• SI UT1-UTC values showed agreement of 32 µs (weighted standard deviation) with conventional Intensives and 27 µs with the 14C04 series.
• The mean scatter of northern hemisphere Intensives relative to C04 was comparable at 29 µs, and SI accuracy was only slightly degraded using the HtHb baseline.

Conclusions:

• The Southern Intensive (SI) program provides UT1-UTC measurements with accuracy comparable to established northern hemisphere VLBI networks.
• The SI program effectively addresses the need for southern hemisphere geodetic data and mitigates potential biases from northern-dominated observations.
• The SI program's operational efficiency and accuracy, even with limited baselines, ensure the rapid provision of essential UT1-UTC data.