A Long-term Analysis of the GPS Broadcast Orbit and Clock Error Variations

The computation of a navigation satellite position and clockis a general task in GPS positioning, and the data needed for this task can be obtained from navigation messagesand IGS precise ephemerides.This study analyzesbroadcast orbit and clock error variations by comparing them with IGS precise ephemerides. Orbit and clock errorsfrom 2001 to 2013 are computed for all GPS satellites as well as for the group of satellites visible inKorea. Orbit and clock errors versus GPS satellite typesare also analyzed. Correlationswith shadow conditions, solar activity, and geomagnetic activityare analyzed.Clock errors and signal-in-spacerange errorsare reduced with the new generation of GPS satellites. The correlations show thatorbit errors increase by 3.2% in shadows.Solar activity and orbit errorhave a high correlation until 2008,but have a low correlation after 2009.