HIGH-FREQUENCY VARIATIONS IN THE ROTATION OF THE EARTH

Observational results are reported demonstrating that a three-station network of properly distributed very-long-baseline interferometry observatories can routinely determine UT1 with a formal standard error of plus or minus 0. 5 ms of time, in an observing period of 24 h. The results are also reported of a three-month series of daily observing sessions of only 1-h duration with a single interferometer, which produced estimates of UT1 with standard errors of plus or minus 0. 1 ms. The UT1 values obtained from the 1-h observing sessions track smoothly between the points of the 24-h time series, and the combined time series shows that it is not unusual for UT1 to vary by 1-2 ms in periods of several days. Preliminary results of reprocessing the 24-h observing sessions in 2-h segments suggest that variations of 0. 4 ms may occur on time scales of only 6-8 h.