Ultra-rapid UT1 measurement by e-VLBI

Using e-VLBI technology, we carried out several ultra-rapid UT1 measurements using the baselines Kashima- Onsala and Kashima-Metsähovi. The observational data were correlated with the Kashima VLBI software correlator in near real-time. After the end of the observing sessions, we performed standard VLBI analysis and we obtained the UT1 results within 30 minutes in the fastest case. The previous record for near real-time UT1 results was 4.5 hours, achieved by Koyama et al., (2004) on the Kashima-Westford baseline. The regular intensive sessions conducted by the International VLBI Service for Geodesy and Astrometry (IVS) usually obtain the UT1 results about a few days after the observations. Thus, with our measurements we greatly improved the latency of UT1 results. We also compared our UT1 results with the combined solution of the International Earth Rotation Service (IERS) Bulletin-A (rapid/predicted values) and Bulletin-B (final values). Our results proved to be consistent with the Bulletin-B values, and the average difference was only 32 microseconds. However, there were large differences between our results and the Bulletin-A predictions. On average the difference was 571 microseconds. For the experiment on 2 May 2007 the difference was more than 1.5 milliseconds, since the experiment was observed just before the next Bulletin-A was published. These comparisons show that it is difficult to use the Bulletin-A UT1 values for near real-time applications. On the other hand we think that our ultra-rapid UT1 results can fulfill quasi-real-time demands. Based on these results we will discuss the application of the results of ultra-rapid UT1 measurements.