Since 1992 the IGS ACs (International GPS Service Analysis Centers) have delivered daily estimates of polar motion (PM) and length of day (LOD) to the IERS (International Earth Rotation Service). The IGS combined PM and LOD series are available since January 1, 1995. Since June 1996 the IGS rapid and the final combined orbits are accompanied with two distinct IGS combined PM series with the same time resolution of one day. Both, the IGS final and rapid combined PM series also include combined PM rate data as well as LOD, starting in March 1997.
Since 1995 the CODE Analysis Center of the IGS has produced PM and LOD estimates with a two-hour time resolution on a routine basis. A study of the time series with sub-daily time resolution clearly shows the half-daily and daily tidal signals. The results correspond very well to those obtained from satellite altimetry.
These sub-daily time series are based on the same observational data from the IGS tracking network as those time series with a one-day time resolution. It would thus be possible with a minor analysis effort, without additional observational effort, to come up with a long and consistent series of PM and LOD with a time resolution of about 1 to 2 hours.