Among GPS error sources, ionospheric and tropospheric error, satellite clock bias and orbital error can be mitigated by differential method. Temporal variation of these errors should be considered important for designing correction message or message scheduling. Because tropospheric error is estimated well by several models, ionospheric delay and satellite-related error need to be analyzed. These error variations depend on the observation site, day of year, time of day, and so on, therefore we need to analyze the rate of change of the error by using the measurements observed in Korea. To calculate the orbit error, precise ephemeris provided by IGS (International GNSS Service) and the broadcast ephemeris from GPS satellite are used. By comparing the distance from a fixed position in Korea to the satellite position estimated by the RINEX data with that by SP3, we found the periodic tendency of the ephemeris variation. While code and phase measurements are generally used to estimate the ionospheric error, we used only phase observations in this paper, for we focused on the rate of the error. To find out the normal, minimum and maximum rate of the ionospheric delay, we chose data from the ionospheric normal, quiet, and strong day. By estimating the error for the whole day, we also show ionospheric diural variation in Korea.

Keywords: satellite orbital error, satellite clock bias, Ionospheric error