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Very Long Baseline Interferometry (VLBI) Intensive sessions are scheduled toprovide operational Universal Time (UT1) determinations with low latency. UT1estimates obtained from these observations heavily depend on the model of thecelestial pole motion used during data processing. However, even the mostaccurate precession-nutation model, IAU 2000/2006, is not accurate enough torealize the full potential of VLBI observations. To achieve the highestpossible accuracy in UT1 estimates, a celestial pole offset (CPO), which is thedifference between the actual and modelled precession-nutation angles, shouldbe applied. Three CPO models are currently available for users. In this paper,these models have been tested and the differences between UT1 estimatesobtained with those models are investigated. It has been shown that neglectingCPO modelling during VLBI UT1 Intensive processing causes systematic errors inUT1 series of up to 20 microarcseconds. It has been also found that usingdifferent CPO models causes the differences in UT1 estimates reaching 10microarcseconds. Obtained results are applicable to the satellite dataprocessing as well.

The impact of celestial pole offset modelling on VLBI UT1 Intensive results