Browsing by Author "Wang, Guangli"

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    Baseline Vector Repeatability at the Sub-Millimeter Level Enabled by Radio Interferometer Phase Delays of Intra-Site Baselines
    (Wiley-Blackwell, 2023-03) Xu, Ming H.; Savolainen, Tuomas; Bolotin, Sergei; Bernhart, Simone; Plötz, Christian; Haas, Rüdiger; Varenius, Eskil; Wang, Guangli; McCallum, Jamie; Heinkelmann, Robert; Lunz, Susanne; Schuh, Harald; Zubko, Nataliya; Kareinen, Niko; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; NASA Goddard Space Flight Center; Reichert GmbH; Federal Agency for Cartography and Geodesy; Chalmers University of Technology; CAS - Shanghai Astronomical Observatory; University of Tasmania; Helmholtz Centre Potsdam - German Research Centre for Geosciences; Technical University of Berlin; National Land Survey of Finland
    We report the results of position ties for short baselines at eight geodetic sites based on phase delays that are extracted from global geodetic very-long-baseline interferometry (VLBI) observations rather than dedicated short-baseline experiments. An analysis of phase delay observables at X band from two antennas at the Geodetic Observatory Wettzell, Germany, extracted from 107 global 24-hr VLBI sessions since 2019 yields weighted root-mean-square scatters about the mean baseline vector of 0.3, 0.3, and 0.8 mm in the east, north, and up directions, respectively. Position ties are also obtained for other short baselines between legacy antennas and nearby, newly built antennas. They are critical for maintaining a consistent continuation of the realization of the terrestrial reference frame, especially when including the new VGOS network. The phase delays of the baseline WETTZ13N–WETTZELL enable an investigation of sources of error at the sub-millimeter level. We found that a systematic variation of larger than 1 mm can be introduced to the Up estimates of this baseline vector when atmospheric delays were estimated. Although the sub-millimeter repeatability has been achieved for the baseline vector WETTZ13N–WETTZELL, we conclude that long term monitoring should be conducted for more short baselines to assess the instrumental effects, in particular the systematic differences between phase delays and group delays, and to find common solutions for reducing them. This will be an important step toward the goal of global geodesy at the 1 mm level.
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    Observable quality assessment of broadband very long baseline interferometry system
    (Springer Verlag, 2021-04) Xu, Minghui; Anderson, James M.; Heinkelmann, Robert; Lunz, Susanne; Schuh, Harald; Wang, Guangli; Department of Electronics and Nanoengineering; Metsähovi Radio Observatory; Anne Lähteenmäki Group; Technische Universität Berlin; GFZ German Research Centre for Geosciences; Chinese Academy of Sciences
    The next-generation, broadband geodetic very long baseline interferometry system, named VGOS, is developing its global network, and VGOS networks with a small size of 3–7 stations have already made broadband observations from 2017 to 2019. We made quality assessments for two kinds of observables in the 21 VGOS sessions currently available: group delay and differential total electron content (δTEC). Our study reveals that the random measurement noise of VGOS group delays is at the level of less than 2 ps (1ps=10-12 s), while the contributions from systematic error sources, mainly source structure related, are at the level of 20 ps. Due to the significant improvement in measurement noise, source structure effects with relatively small magnitudes that are not overwhelming in the S/X VLBI system, for instance 10 ps, are clearly visible in VGOS observations. Another critical error source in VGOS observations is discrete delay jumps, for instance, a systematic offset of about 310 ps or integer multiples of that. The predominant causative factor is found to be related to source structure. The measurement noise level of δTEC observables is about 0.07 TECU, but the systematic effects are five times larger than that. A strong correlation between group delay and δTEC observables is discovered with a trend of 40 ps/TECU for observations with large structure effects; there is a second trend in the range 60–70 ps/TECU when the measurement noise is dominant.