COMPARISON OF TERRESTRIAL REFERENCE FRAME VELOCITIES DETERMINED FROM SLR AND VLBI

The most recent site velocity solutions from the VLBI analysis group a t the Goddard Space Flight Center and the SLR analysis group at the Un iversity of Texas Center for Space Research are compared. The results indicate that the horizontal velocities agree, after removing a veloci ty transformation of a few millimeters per year, to the 2-3 millimeter per year level in an rms sense. The velocities of the best observed s ites agree to nearly 1 mm/yr in each horizontal component. In addition , when only sites with adjusted velocities are compared, the agreement of epoch site positions is improved over previous studies to the subc entimeter level in the horizontal components. The sites in the western United States agree at the few millimeter level.