Abstract
Satellite orbit and clock corrections are always treated as known quantities in GPS positioning models. Therefore, any error in the satellite orbit and clock products will probably cause significant consequences for GPS positioning, especially for real-time applications. Currently three types of satellite products have been made available for real-time positioning, including the broadcast ephemeris, the International GNSS Service (IGS) predicted ultra-rapid product, and the real-time product. In this study, these three predicted/real-time satellite orbit and clock products are first evaluated with respect to the post-mission IGS final product, which demonstrates cm to m level orbit accuracies and sub-ns to ns level clock accuracies. Impacts of real-time satellite orbit and clock products on GPS point and relative positioning are then investigated using the P3 and GAMIT software packages, respectively. Numerical results show that the real-time satellite clock corrections affect the point positioning more significantly than the orbit corrections. On the contrary, only the real-time orbit corrections impact the relative positioning. Compared with the positioning solution using the IGS final product with the nominal orbit accuracy of ~2.5 cm, the real-time broadcast ephemeris with ~2 m orbit accuracy provided <2 cm relative positioning error for baselines no longer than 216 km. As for the baselines ranging from 574 to 2982 km, the cm–dm level positioning error was identified for the relative positioning solution using the broadcast ephemeris. The real-time product could result in <5 mm relative positioning accuracy for baselines within 2982 km, slightly better than the predicted ultra-rapid product.
Highlights
International GNSS Service (IGS), as a voluntary federation, has been providing the GNSS community with valuable data and products ever since 1994, including raw observation data, GNSS satellite orbit and clock products, Earth rotation parameters, and atmospheric parameters [1]
This paper aims to study the impacts of satellite orbit and clock products on real-time GPS point and relative positioning
The cm-level relative errors are obtained for baselines no longer than 216 km, and issue of satellite orbit and clock products which are observed to be un-negligible for point positioning cm- to dm-level errors for baselines beyond 216 km
Summary
International GNSS Service (IGS), as a voluntary federation, has been providing the GNSS community with valuable data and products ever since 1994, including raw observation data, GNSS satellite orbit and clock products, Earth rotation parameters, and atmospheric parameters [1]. Aiming at the substitution of the IGU product, the IGS real-time products have been extensively investigated during past years, in terms of real-time positioning [16,17,18,19,20,21], real-time troposphere estimation [22,23,24,25,26], and real-time seismology [27] applications Both the satellite orbit and clock products would affect positioning solutions as these two terms are normally treated as known quantities in GPS positioning models. This paper aims to study the impacts of satellite orbit and clock products on real-time GPS point and relative positioning.
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