Improved steerign of the IGS timescales to UTC

Summary form only given. Currently the International GPS Service (IGS) timescales are aligned to the international timescale UTC by slowly steering (roughly consistent with a 30-40 d time constant) to observations of GPS time, which is itself steered to UTC via the UTC (USNO) realization. The instability of the IGS timescales has been determined to better than 2 parts in 10¹⁵ at 1 d, whereas the instability of GPS time is at least 10 times poorer. It is likely that due to its larger instability, steering to GPS time limits the stability of the IGS timescales for periods longer than a few days. A new method (the topic of another paper at this conference) extends to geodetic systems the timing calibration from systems colocated at timing laboratories that contribute to UTC. These colocated geodetic systems and local UTC (k) realizations can have much better stabilities than GPS time. Using the empirical instrumental calibration biases together with predictions of UTC (k) offsets, suitable colocated geodetic clock data can provide a higher- quality and robust link of the IGS timescales to UTC. We discuss the techniques used to predict offsets of UTC (k) between monthly Circular T reports and assess the stability and overall quality of the IGS timescales as steered using these differentially calibrated systems instead of GPS time.