Improving geodetic VLBI: UT1 accuracy, latency of results, and data quality monitoring

Minttu Uunila

    Research output: ThesisDoctoral ThesisMonograph

    Abstract

    In modern geodesy the space-related techniques play an important role. The three most significant of these techniques are the Global Navigation Satellite System (GNSS) that includes the Global Positioning System (GPS), the Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). The next generation geodetic VLBI system, VLBI2010, covers everything from antennas to analysis and is being implemented at VLBI stations globally. One of the key requirements for VLBI2010 is the automation of the data analysis in order to reduce the latency of the results to 24 hours. VLBI is a unique technique for determining the Earth Orientation Parameters (EOP), which are necessary, for example, for navigation satellites. The accuracy of GNSS positioning is related to the accuracy of EOP. Therefore, it is important to measure these parameters with the best possible accuracy and as short latency as possible. In this dissertation the automation of the International VLBI Service for geodesy and astrometry (IVS) intensive sessions is described. In the near future, the Vienna VLBI Software (VieVS) will be implemented with the pre-analysis steps that are currently being developed, the group delay ambiguity resolution and the ionospheric correction. The most commonly used geodetic VLBI analysis software is Calc/Solve that is maintained at the Goddard Space Flight Center (GSFC). So as not to bias the outcome by adopting only one software package, a comparison of Solve and VieVS EOP results was performed. This comparison showed that VieVS analysis appeared to improve the accuracy in the dUT1 result. However, polar motion results were more precise when Solve was used for the analysis. To fulfill the VLBI2010 precision requirements, the effect of source distribution on the dUT1 result accuracy obtained from IVS INT1 experiments was investigated. On the basis of the research conducted in this thesis, the results from the source constellation study show that the accuracy of the dUT1 is affected by the distribution in the sky as seen from the midpoint of a baseline, and will improve when a novel method proposed for scheduling intensive sessions will be implemented. Until now, the sky has been observed from the Kokee Park North direction. Introducing the new concept of observing the sky from a fictitious midpoint of the baseline greatly improves dUT1 accuracy. IVS should take this into consideration, because the accuracy of the results is a significant factor when calculating satellite orbits, for example. VLBI2010 requires shipment of the VLBI data via Internet. Firmware was developed to enable VLBI2010-compatible stations to perform zero baseline correlation tests with the Digital Base Band Converter (DBBC) and FILA10G ethernet board, and thus the stations can check the quality of the data in real-time.
    Translated title of the contributionGeodeettisen VLBI:n kehittäminen: UT1:n tarkkuus, tulosten viiveellisyys ja datan laadun monitorointi
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Hallikainen, Martti, Supervising Professor
    • Tornikoski, Merja, Thesis Advisor
    • Poutanen, Markku, Thesis Advisor, External person
    Publisher
    Print ISBNs978-952-60-5179-6
    Electronic ISBNs978-952-60-5180-2
    Publication statusPublished - 2013
    MoE publication typeG4 Doctoral dissertation (monograph)

    Keywords

    • Very Long Baseline Interferometry
    • VLBI
    • geodesy
    • UT1
    • VHDL
    • VHSIC Hardware Description Language

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