High-rate clock variations of the Galileo IOV-1/2 satellites and their impact on carrier tracking by geodetic receivers
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The carrier signals of the first two Galileo satellites, IOV-1 and IOV-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 cross talk of signals from two active atomic frequency standards in the clock monitoring and control unit (CMCU). This cross talk 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 relevant to 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 earthquake research. We present practical measurements from zero-baseline tests of common geodetic receivers with data rates of 1/30–1 Hz as well as dedicated tests with high-rate (50–100 Hz) receivers to evidence the phenomenon. Efforts are made to understand the different response of specific receivers based on generic receiver tracking and measurement generation concepts.
KeywordsGalileo Clock oscillation CMCU
Individual receivers used in this study have been contributed by the DLR Institute of Communication and Navigation as well as Leica Geosystems. The support of both institutions is gratefully acknowledged. Furthermore, the authors would like to thank Dr. Francisco Javier Gonzalez Martinez of ESA/ESTEC for valuable technical comments and his thorough review of an initial manuscript version.
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