Monitoring Earth orientation through the end of the century

Abstract

In 1992 Very Long Baseline Interferometry (VLBI) is the “method of choice” to monitor polar motion (PM), Universal Time (UT1), precession and nutation. International VLBI networks routinely produce PM and nutation values accurate to 0.3–0.5 milli-arc-seconds (mas) and UT1 accurate to 0.05 milliseconds (ms), at 3.5 day intervals, and daily UT1 values accurate to 0.05–0.10 ms. Only cost considerations prevent sub-daily PM and UT determinations. Future improvements in VLBI should achieve 0.05–0.10 mas accuracies, and near real time correlation could reduce processing delays to 24 hours; the Global Positioning System (GPS) may provide PM at 2–6 hour intervals, while single baseline VLBI observations could provide UT1 values at comparable intervals. Eventually the combination of real-time processing of GPS plus superfluid gyroscope data may provide nearly continuous PM and UT1 tracks for periods of weeks; infrequent VLBI sessions will be needed for monitoring precession, nutation, and the celestial and terrestrial reference frames.