Flight Characterization of New Generation Satellite Clocks

Abstract

The passive hydrogen maser (PHM) of GIOVE-B and the latest generation of Rubidium clocks for GPS Block IIF satellites have both demonstrated a superior and highly competitive stability in ground tests. In practice, however, the apparent clock performance for GNSS users is limited by measurement errors and imperfections of the signal chain that affect the clock variance at different time scales. Within this paper, we provide a direct comparison of the apparent clock performance for GIOVE-B and the first Block IIF satellite (SVN62). The analyses are based on observations of the IGS and CONGO network. Periodic errors in the apparent clocks of both satellites are analyzed and an effort is made to separate the impact of orbit determination errors from physical clock or line bias variations. For SVN62 an empirical clock correction model is discussed, which offers a notable reduction of the Allan variance at orbital time scales. Furthermore, triple-frequency observations are used to demonstrate the presence of thermally induced line bias variations and to quantify the resulting inter-frequency clock biases.