IGS Combinations of Polar Motion, Length of Day and Universal Time

Abstract

Since March 1997, the International GPS Service (IGS) has officially introduced new Length Of Day (IGS LOD) and Universal Time (IGS UT) combination products based on a weighted average of available Analysis Centre’s (AC) LOD solutions. Each AC LOD series is calibrated with respect to the IERS Bulletin A over a 21-day period. IGS UT is estimated by integrating the IGS combined LODs from a chosen IERS Bulletin A reference point (also called the anchor point). Several processing and combination strategies were tested and implemented in the Rapid (available 22 hours after the last observation) and the Final (available 10 days after the last observation) IGS LOD/UT combinations. IGS LOD and UT precision is at or below the 100 and 30 µsec levels respectively for both the Rapid and Final combinations when compared to the IERS Bulletin A. The IGS has also been combining Polar Motion (PM) x and y since May 1995 and PM rates since June 1996. Steady improvements were made throughout the years resulting in an IGS PM precision, when compared to the IERS Bulletin A, at or below the 0.3 and 0.1 mas levels for the Rapid and Final combinations respectively. The PM and LOD/UT combinations are described and results are presented.