COMPARISON OF GPS SATELLITE COORDINATES COMPUTED FROM BROADCAST AND IGS FINAL EPHEMERIDES

Abstract

There are mainly two different orbital information, namely broadcast ephemerides and IGS final ephemerides (IGS rapid, ultra rapid, predicted and final ephemerides) used in the GPS positioning. The broadcast ephemerides used in practice and real time are obtained through assessments derived from the observations from the USA GPS reference stations. Broadcast ephemerides are formed (depending on GPS week) from satellite information and the accuracies they provide are adequate in many GPS applications. On the other hand, several parameters (for example, information about gravity area, improved satellite orbit information, etc.) need to be known in order to attain high accuracy in engineering and geodetic applications. Final ephemeris information can be downloaded from the related web sites via the internet. In this study, Keplerian motion and Keplerian orbital parameters will be explained briefly and extensive information about ephemerides and numerical applications will be given. Within this scope, for GPS satellites, ECEF coordinates of the satellites were computed using the broadcast ephemerides. The coordinates computed by using broadcast ephemerides were compared with the coordinates obtained from the IGS final orbits.