Interferometric Determination of GPS (Global Positioning System) Satellite Orbits.

Abstract : One way phase observations of GPS satellites at three ground stations were differenced between stations to form interferometric observations. These single difference observations were differenced between satellites to form double difference observations. We analyzed the one way, single, and double difference observations by least-squares to determine the orbits of satellites. In most cases the formal standard errors of the estimated satellite positions were of the order of several meters---equivalent to a few parts in 10 million of the orbit radius. The actual errors of the estimated orbits are unknown, but we were able to test the day to day precisions by using these orbits to analyze observations from an independent pair of stations, to determine the baseline vector between them. The results of this analysis confirmed the uncertainty estimate of a few parts in 10 million. Further confirmation was obtained from a comparison of orbits estimated from disjoint, but interleaved, spans of observations. Keywords: Geodesy, Geodetic control; Geodetic networks; Three dimensional geodesy; Satellite geodesy, NAVSTAR Global Positioning System; Interferometry; Satellite orbits; Satellite orbit determination.