SUB-DAILY RESOLUTION OF EARTH ROTATION VARIATIONS WITH GLOBAL POSITIONING SYSTEM MEASUREMENTS

Data from a worldwide Global Positioning System (GPS) tracking experim ent have been used to determine variations in Earth rotation (UT1-UTC) over a time period of three weeks. Kalman filtering and smoothing ena bled changes in UT1-UTC over intervals of 2 to 24 hrs to be detected w ith the GPS data. Internal consistency checks and comparisons with oth er solutions from very long baseline interferometry (VLBI) and satelli te laser ranging (SLR) indicate that the GPS UT1-UTC estimates are acc urate to about 2 cm. Comparison of GPS-estimated variations in UT1-UTC with 2-hr time resolution over 4 days with predicted variations compu ted from diurnal and semi-diurnal oceanic tidal contributions strongly suggests that the observed periodic sub-daily variations of approxima tely 0.1 msec (5 cm) are largely of tidal origin.