VLBI satellite tracking for the realization of frame ties
Creators: name: McCallum, Lucia
Publisher: name: University Of Tasmania
Year: 2023
Subjects: Astronomical sciences not elsewhere classified

description: VLBI satellite tracking is a popular topic in geodesy at the moment. Attributed with the potential to solve the pending problem of inter-technique frame ties, the prospect of success provides the impetus of ongoing research in that area. Very Long Baseline Interferometry (VLBI) is a well-probed space geodetic technique used to determine the Celestial Reference Frame (CRF), the Terrestrial Reference Frame (TRF) and the Earth Orientation Parameters (EOP) in between. Alternatively, VLBI is generally used in spacecraft tracking. Technology in that area has been rapidly advancing in the last years. An overview of present realizations of VLBI spacecraft tracking, including data processing on the example of the Japanese lunar mission SELENE is part of this work. Today’s most precise and reliable realizations of the TRF rely on the measurements of several space geodetic techniques and the corresponding inter-technique ties. For future improvement, and also for a rigorous determination of the whole system of CRF-EOP-TRF, alternative methods for connecting the various space geodetic techniques, establishing precise frame ties, are urgently needed. A promising solution is the use of VLBI satellite observations, either in combination with a so-called space tie realized by a dedicated satellite or by directly observing satellites of the Global Navigation Satellite Systems (GNSS) with VLBI. The study of successful realizations of VLBI tracking and identifying proper applications for practical geodetic value summarizes this work. With the goal to process real data, the Vienna VLBI Software VieVS is extended for the possibilities to schedule, simulate and analyze VLBI satellite observations. Some details on the corresponding delay modeling are provided. The technique of VLBI satellite tracking is introduced, discussing some practical issues as well as the latest developments. This thesis contains a detailed simulation study of VLBI observations to satellites, identifying adequate observing strategies for the precise determination of antenna coordinates on Earth in the satellite’s system. For satellites at heights between 1000 and 20000 km, adequate observation strategies are found that allow the determination of the station coordinates at the level of a few millimeters. Therefore, the approach of weekly solutions in chosen, meaning that one satellite is observed by either a regional or a global antenna network during seven consecutive days. For the investigated satellites at 2000 and 6000 km, a feasible observing interval of 1 minute is found. Assuming turbulent tropospheric conditions, in regional networks of 6-7 stations with baseline lengths between 2000 and 3000 km, weekly 3D position rms between 3 and 14 mm can be expected, depending on the orbit, respectively the height, of the observed satellite, as well as on the changing geometry between the observing baselines and the target satellite. For global networks, a considerable high number of observing telescopes is needed, about 16-32, with expected accuracies at the same level as in regional networks for a higher satellite at 6000 km height and about a factor of two worse for a very low satellite at 2000 km. In the case of VLBI observations to a satellite of the GNSS, alternative observing strategies are needed. In this thesis the combination with a classical VLBI session observing extragalactic radio sources or the observation of a satellite constellation are introduced. The careful assessment of the presented results reveals valuable application of such observations in the area of frame ties, strongly supporting immediate realization and ongoing research on the topic of VLBI satellite observations.