Matthias Madzak
Type of contribution: oral
Session: 3

Universal Time from VLBI Intensives with ray-traced delays

Matthias Madzak, Vienna University of Technology Vahab Nafisi, The University of Tehran, Iran Johannes B\"ohm, Vienna University of Technology Harald Schuh, Vienna University of Technology

VLBI Intensive sessions are used for the estimation of UT1-UTC (DUT1) which is needed in near real-time for the accurate prediction of Universal Time (UT1) as well as for navigation purposes. These 1-hour IVS sessions (INT1 and INT2) are carried out every day to provide this quantity on a regular basis. Due to the small number of observables per session most parameters, which are usually estimated in VLBI analyses, are fixed to their a priori values. This means that all a priori values should be known as accurately as possible to derive accurate DUT1 estimates. One possibility of deriving a priori tropospheric delays is ray-tracing through numerical weather models. These tropospheric delays also account for azimuthal asymmetries, what might as well increase the accuracy of DUT1 estimates. We analyze Intensive sessions from July 2010 to October 2011 using the Vienna VLBI Software (VieVS) and compare the obtained DUT1 values based on ray-traced delays to those from standard approaches. Furthermore we calculate Length-of-Day (LoD) from DUT1 and compare these values to LoD from GPS.