An experiment which uses the methodology gained from VLBI to try to improve determinations of the vertical from GPS will conducted. The experiment involves establishing a network of homogeneous GPS sites, with each GPS receiver being located at one of the VLBI sites participating in the low-elevation-angle VLBI "R&D" experiments. These experiments, and their predecessors, have been extremely useful in developing methods for improving the accuracy of vertical estimates from VLBI. By analyzing and comparing estimates obtained from both the GPS and the VLBI data sets, methods for obtaining the most accurate determinations of the vertical from GPS will be developed.
