Yvonne Vigue

First assessment of GPS‐based reduced dynamic orbit determination on TOPEX/Poseidon

The reduced dynamic GPS tracking technique has been applied for the first time as part of the GPS experiment on TOPEX/Poseidon. This technique employs local geometric position corrections to reduce orbit errors caused by the mismodeling of satellite forces. Results for a 29-day interval in early 1993 are evaluated through postfit residuals and formal errors, comparison with GPS and laser/DORIS dynamic solutions, comparisons on 6-hr overlaps of adjacent 30-hr data arcs, altimetry closure and crossover analysis. Reduced dynamic orbits yield slightly better crossover agreement than other techniques and appear to be accurate in altitude to about 3 cm RMS.

Precise determination of Earth's center of mass using measurements from the global positioning system

Global Positioning System (GPS) data from a worldwide geodetic experiment were collected during a 3-week period early in 1991. Geocentric station coordinates were estimated using the GPS data, thus defining a dynamically determined reference frame origin which should coincide with the earth center of mass, or geocenter. The 3-week GPS average geocenter estimates agree to 7-13 cm with geocenter estimates determined from satellite laser ranging, a well-established technique. The RMS of daily GPS geocenter estimates were 4 cm for x and y, and 30 cm for z.

GPS measurements of the baseline between Quincy and Platform Harvest

As part of TOPEX altimeter verification, the global positioning system has been used to measure the baseline between the verification site at oil Platform Harvest and a GPS antenna collocated with the satellite laser ranging site at Quincy, California. Data from Harvest, Quincy, and a global network of stations, collected between September 25, 1992 and December 17, 1993, have been analyzed to obtain 272 single‐day estimates of the baseline. These daily estimates have in turn been fitted with a linear model, yielding a single estimate of the baseline and its rate of change. Changes in the horizontal components of the baseline reflect the relative tectonic motion of the Pacific plate and the Sierra Nevadan microplate, along with local motion at Harvest and Quincy. The vertical component, crucial to verification, is determined with millimeter‐level accuracy and shows no significant variation during the measurement interval.