Future GNSS Infrastructure for Improved Geodetic Reference Frames

Abstract

In this study, the expected improvement of the future GNSS infrastructure “Kepler” on global geodetic reference frames with the focus on the Earth rotation parameters (ERP: pole coordinates x p ’ yp and UT1-UTC) is assessed by simulations. Kepler features a Medium Earth Orbit (MEO) and Low Earth Orbit (LEO) segment and is characterized by the innovative key technologies of optical inter-satellite links (ISL) and optical frequency references as proposed by the German Aerospace Center DLR. The standard deviations of the estimated pole coordinates from the Kepler constellation are below 1 µas compared to µas in xp and 15 µas in yp from the MEO-only solution. The standard deviation of the UT1-UTC estimates in case of the full Kepler constellation is 0.3 µs compared to 1.8µs in case of MEO-only. The highly precise Kepler technique with stable orbits together with the globally distributed station network is very beneficial for the estimation of the ERP, especially the pole coordinates. UT1-UTC cannot be absolutely estimated from any satellite technique alone and needs to get fixed to at least the first value to external data. UT1-UTC can only be estimated absolutely from the space technique Very Long Baseline Interferometry (VLBI) which was simulated as well in case of two different scenarios (classical and next generation) and combined with the MEO-only and the Kepler solution. VLBI lacks in the spatial and temporal resolution of observations limiting the accuracy of the pole coordinates compared to GNSS. In the combined Vl. Bl+Kepler solution the mean value of 50 µas in xp (VLBI-only) is reduced to −2 µas and the standard deviation from 62 µas (VLBI-only) reduced below 1 µas. The combination with Kepler leads to improved pole coordinate estimates of VLBI. The combination with VLBI allows the estimation of UT1-UTC for Kepler without external information. The standard deviation of the UT 1- UTC estimates is improved from 1.5 µs for MEO+ VLBI to 0.3 µs for Kepler+ VLBI. Further improvements can be noticed in case of the combination with a next generation VLBI solution.