Comparison of the GLONASS orbit products for UTC time transfer

Accurate GNSS (Global Navigation Satellite System) time transfer needs accurate satellite orbit information. Since Nov. 2009, the GLONASS time transfer is introduced in UTC generation. The precise and timely GLONASS orbit information is indispensable for Circular T computation. In this paper, we compare the GLONASS orbits produced by different analysis centers. We study the differences of the products, their influences on the common view time transfers and the delays of the availability. The products to investigate are the rapid and final sp3 ephemeredes produced by ESA (Europe Space Agency) and IAC (Information-Analytical Center). IAC belongs to Russia Federal Space Agency. Its primary goal is to analyze the information on the satellite navigation based on the global systems, mainly the GLONASS. The delay of the IAC sp3 rapid products is 24-28 hours. This satisfies the rhythm of the BIPM monthly Circular T computation, of which the deadline of data collection is the 5^th of every month. Since Nov. 2010, the BIPM started to use the IAC ephemeredes to compute the GLONASS satellite orbits for UTC time transfer. At present the IAC product is the most suitable for the UTC GLONASS time link computations.