EARTH ORIENTATION DETERMINATIONS BY SHORT-DURATION VLBI OBSERVATIONS

In May 1989 and April 1990 the radio telescopes of the Wettzell Geodet ic Fundamental Station in Germany and of the Shanghai Observatory near Seshan in China observed two series of daily VLBI experiments of shor t duration for precise determination of UTI. In 1990 a few experiments were complemented by the Hartebeesthoek Radio Astronomy Observatory i n South Africa and the Medicina telescope of the Bologna Istituto di R adioastronomia in Italy. Employing the South African station together with the east-west baseline formed by the observatories of Seshan and Medicina permitted simultaneous determinations of UTI and polar motion . Here we report on the results of these observations. Comparing the U T1 results with those of the IRIS Intensive series gives a clear indic ation of the absolute accuracy of such short duration VLBI measurement s which is estimated to be of the order of +/- 60 mu s.