TOWARDS GPS ORBIT ACCURACY OF TENS OF CENTIMETERS

The Global Positioning System (GPS) will be used in the coming decade for mm‐level measurements of crustal motion and for sub‐decimeter earth orbiter positioning and navigation. GPS orbits for these applications will be required accurate to 10–20 cm. Although sub‐meter GPS orbit precision has been previously demonstrated with a regional tracking network, several factors are expected to play a role in further improvement to the several decimeter level. These include the use of worldwide ground tracking networks and improved orbit modeling. In this paper, CASA UNO orbit results are presented utilizing data from four continents. Refinements in orbit modeling, combined with the availability oft worldwide tracking network and the dense distribution of tracking sites in North and South America, have improved orbit determination precision to about 60 cm (per component) for four of the seven GPS satellites tracked in CASA UNO. The orbit results are consistent with California baseline repeatabilities, which are at the few mm level in horizontal and length, and 1–2 cm in the vertical. Baseline comparisons with VLBI provide a measure of orbit accuracy, showing sub‐cm agreement in length and 1.5 cm agreement in the horizontal. Copyright 1990 by the American Geophysical Union.