The investigation of the accuracy of the GPS broadcast ephemerides using for different epochs

GPS has two different orbit information in terms of precise ephemeris and broadcast ephemeris. In many practical GPS applications, the accuracy of broadcast ephemeris is sufficient. IGS precise ephemeris is used in applications where high accuracy is expected. The broadcast ephemeris is generated by the satellite information that is referenced by the evaluation of the data derived from the observations in the monitoring stations and is published in real time. Precise ephemeris generated by evaluating the observations made at 30 second intervals for 24 hours using IGS data. In this study, it is aimed to investigate the effects of broadcast and precise ephemeris data on station coordinates. ECEF coordinates of satellites were calculated at 15 minutes intervals between 22:00 on December 31, 2017 and 02:00 on January 1, 2018. Thus, the differences between the broadcast ephemeris and the precise ephemeris data were examined for both at the ephemeris epoch and for different epochs. The minimum and maximum differences of X, Y, Z values showed irregular distribution and mean values were obtained as nearly zero in three components. In cases where the time variable (t) changed in the calculations was positive, the difference was found to be below 3 m, whereas in cases where t value was negative, this difference approached 3.8 m. The standard deviation gave approximately the same values in all three components, and the standard deviation value increased as it differs from the zero epoch was increased.