Precise regional baseline estimation using a priori orbital information

A solution using GPS measurements acquired during the CASA Uno campaign has resulted in 3-4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline, located in North America. The agreement with VLBI is at the level of 10-20 mm for all components. The results were obtained with the GIPSY orbit determination and baseline estimation software and are based on five single-day data arcs spanning the 20, 21, 25, 26, and 27 of January, 1988. The estimation strategy included resolving the carrier phase integer ambiguities, utilizing an optial set of fixed reference stations, and constraining GPS orbit parameters by applying a priori information. A multiday GPS orbit and baseline solution has yielded similar 2-4 mm horizontal daily repeatabilities for the same baseline, consistent with the constrained single-day arc solutions. The application of weak constraints to the orbital state for single-day data arcs produces solutions which approach the precise orbits obtained with unconstrained multiday arc solutions.