Developing an IGS time scale

Currently, the International GPS Service (IGS) provides a set of clock products for both satellites and tracking receivers, tabulated at 5-minute intervals. These products provide users with sufficient information to determine consistent coordinates and clock values for an isolated GPS receiver with a precision at roughly the 5-cm level. However, because the underlying time scale for the IGS combined clocks is based on a linear alignment to broadcast GPS time for each day separately, the day-to-day stability of this reference is poor. We show the results of a new filter package written to automate the production of an integrated IGS frequency scale loosely steered to GPS time and to which the IGS clock products will soon be referenced