Station coordinates, baselines, and Earth rotation from LAGEOS laser ranging: 1976–1984

Satellite laser range (SLR) measurements to LAGEOS from May 1976 to January 1984 have been used to compute earth rotation parameters and the geocentric positions of 57 laser tracking station sites occupied during this interval. The station position determinations were part of a simultaneous solution which includes LAGEOS orbit elements in 15-day arcs and earth rotation parameters in 3-day subarcs using residuals from a 7.7-year LAGEOS long arc (LLA 8402). Systematic differences between the terrestrial reference frames implied by the University of Texas station coordinate solution (LSC 8402) and by previous solutions computed at the University of Texas (UT) and at Goddard Space Flight Center (GSFC) are reviewed. The new solution resolves a 0.72 m z axis difference between the terrestrial reference system origins inferred from the GSFC solution (SL5) and the previous UT solution (LSC 8112). The implied origins of the LSC 8402 solution and the SL5 solution are consistent to less than 60 mm in all components, and after removing orientation and scale differences, the coordinates for 26 common tracking stations have an rms difference of less than 80 mm. The rms difference in baseline length for 22 station pairs used in the recent Crustal Dynamics Project very long baseline interferometry (VLBI)/SLR intercomparison experiment is 50 mm between the GSFC and UT laser solutions and 40 mm between the UT laser solution and the VLBI solution. The earth rotation parameters computed in 3-day intervals have an internal precision of 2 marc sec (62 mm at the earth's surface) for xp and yp and 0.15 ms (70 mm at the equator) for UT1. The estimated accuracy of the series, based on dual-baseline VLBI intercomparisons, is approximately 2 marc sec for xp and yp and 0.2 ms for UT1. The effects of plate motion on the determination of the secular drift in polar motion using the 7.7-year series is shown to be at the level of 1 marc sec/yr. Finally, baseline changes have been investigated by repeated station coordinate determinations using 60-day subsets of the 7.7-year interval of the LAGEOS data set. In each 60-day solution interval, orbit elements were estimated at 15-day intervals, and earth rotation parameters were determined at 5-day intervals. For the 4-year period beginning in January 1980, baseline length changes inferred by the successive 60-day solutions were found to be in general agreement with the motions predicted by the AM1-2 plate motion model of Minster and Jordan.