Establishing a GPS-Baseline between Seattle, Washington and Monterey, California

A baseline of about 1200 km between Seattle, Washington, and Monterey, California, was measured repeatedly over a six-month period using five-channel, single-frequency Global Positioning System GPS receivers with carrier phase differencing techniques and broadcast ephemeris. The averaged GPS baseline length compared favorably with the length determined from control points established by Very Long Baseline Interferometry VLBI, the agreement being on the order of 0.01 ppm 1cm in 1200 km which is about the precision expected of the VLBI technique itself. The quality of the agreement is startling, considering the relatively poorer precision about 1 ppm expected for the GPS receivers and techniques employed. To achieve this agreement, TPS observations varying more than 1 ppm from the computed mean length were discarded, and a scale factor of -0.2 ppm for the transformation from GPS to VLBI reference frames was applied, which had been estimated from other studies. The results suggest that accuracies of better than a decimeter are achievable over lines of 1000 km using single-frequency GPS equipment. Keywords Single difference Double difference Triple difference Baseline Washington state. Theses.