High-rate clock variations of the Galileo IOV-1/2 satellites and their impact on carrier tracking of geodetic receivers

Abstract

The carrier signals of the first two Galileo satellites, IOV-1 and -2, exhibit subtle phase variations, which may cause high-rate oscillations in carrier-phase measurements of geodetic-grade receivers as well as associated Doppler measurement errors. The carrier-phase oscillations slightly exceed the noise level of the measurements and have been attributed to a subtle crosstalk of signals from two active atomic frequency standards in the Clock Monitoring and Control Unit. This crosstalk is only present in the first two IOV satellites and its practical implications have partly been compensated by now through a suitable configuration of the CMCU. Nevertheless, a proper understanding of the phenomenon is deemed of relevance for the interpretation of Galileo IOV measurements collected with global ground networks in the 2012 to early 2015 time frame. Also, the data collected so far offer valuable insight into the tracking of high-frequency signal variation of geodetic receivers that are of interest for applications such as structural monitoring or Earth quake research. Within the paper, practical measurements from zero-baseline tests of common geodetic receivers with data rates of 1/30 Hz to 1 Hz as well as dedicated tests with high-rate (50–100 Hz) receivers are presented to evidence the phenomenon. Efforts are made to understand the different response of specific receivers based on generic receiver tracking and measurement generation concepts.