We processed pseudorange and phase GPS data in single-day solutions using the GAMIT software. We processed data from the 12 campaign sites observed in October as well as data from the 4 continuous GPS stations currently operating in the Dominican Republic (see above). We solved for regional station coordinates, satellite state vectors, 7 tropospheric zenith delay parameters per site and day, and phase ambiguities using doubly-differenced GPS phase measurements. We used IGS final orbits, IERS (International Earth Rotation Service) earth orientation parameters, and applied azimuth-dependent antenna phase center models, following the tables recommended by the IGS. We included 11 global IGS stations with position and velocities well determined in the International Terrestrial Reference Frame (ITRF2000; Altamimi et al., 2002) to serve as ties with the global reference frame (stations GOLD, BRMU, ALGO, CRO1, KOUR, MAS1, RSM5, RCM6, AREQ, SANT, KOKB).
The least squares adjustment vector and its corresponding variance-covariance matrix for station positions and orbital elements estimated for each independent daily solution were then combined with daily solutions from global tracking sites obtained from the IGS data processing center at Scripps Institution of Oceanography. Site positions and velocities, earth orientation parameters, and orbits are loosely constrained at this stage.
We then impose the reference frame using the resulting combined solution by minimizing the position and velocity deviations of 14 IGS stations with respect to the ITRF2000, while estimating an orientation, translation and scale transformation. The height coordinate and velocity were down-weighted by a factor of 10 relative to the horizontal components in the transformation. The post-fit RMS of the reference frame stabilization is 5.3 mm. The final results are therefore a set of positions expressed in the ITRF2000 reference frame at the epoch of data collection.