Global Navigation Satellite System data consists of the U.S. Global Positioning System (GPS) and the Russian GLObal NAvigation Satellite System (GLONASS) data sets. The satellites transmit the ranging codes on two radio-frequency carriers, allowing the locations of GNSS receivers to be determined with varying degrees of accuracy, depending on the receiver and post-processing of the data.
Analysis ... Centers (ACs) of the International GNSS Service (IGS) retrieve GNSS data on regular schedules to produce precise orbits identifying the position and velocity of the GNSS satellites. These orbits are determined sub-daily (ultra-rapid generation), daily (rapid generation), and weekly (final IGS product). The IGS Analysis Center Coordinator retrieves these individual solutions and generates the official IGS combined orbit products. The orbits generated by the individual ACs and the combination products generated by the ACCs are available at the CDDIS. These orbits can be used to determine precise coordinates of the observing stations, gravity field parameters, and Earth orientation parameters.