Improving VLBI analysis by tropospheric ties in GNSS and VLBI integrated processing
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Abstract Tropospheric delay modeling is challenging in high-precision Very Long Baseline Interferometry (VLBI) analysis due to the rapid water vapor variation and imperfect observation geometry, where observations from Global Navigation Satellite Systems (GNSS) co-locations can enhance the VLBI analysis. We investigate the impact of tropospheric ties in the VLBI and GNSS integrated processing during the CONT05–CONT17 campaigns, and present a method that automatically handles the systematic tropospheric tie biases. Applying tropospheric ties at VLBI–GNSS co-locations enhances the observation geometry and improves the solution reliability. The VLBI network is stabilized, with station coordinate repeatability improved by 12% horizontally and by 28% vertically, and the network scale improved by 32%. The Earth Orientation Parameters (EOP) improve by up to 20%. Both zenith delay and gradient ties contribute to the improvement of EOP, whereas the gradient ties contribute mainly to the improvement of length of day and celestial pole offsets.Keywords:
Very-long-baseline interferometry
Zenith
Dilution of precision
Abstract In view of many problems associated with the availability of global navigation satellite system (GNSS) signals in high-altitude space, this paper presents a comprehensive and systematic analysis. First, the coverage and strength characteristics of GNSS signals in high-altitude space (i.e., space above the GNSS constellation) are presented, and the visibility of GNSS signals is evaluated by combining these two factors. Second, the geometric configuration and geometric dilution of precision (GDOP) of visible GNSS satellites are analysed. Then, the Doppler shift range of the GNSS signals is deduced based on the dynamic performance of high-altitude spacecraft. Finally, taking GaoFen-4 (GF-4) as the application object, the availability of GNSS signals is simulated and evaluated. GNSS signals in high-altitude space are generally weak, and the visible GNSS satellites are concentrated in the high-elevation range. The combination of main and side lobe signals and compatibility of multiple constellations can increase the number of visible satellites, improve the geometry configuration, reduce GDOP, and thus improve the availability of GNSS signals. The results of this research can provide technical support for the design and development of GNSS receivers suitable for high-altitude space.
Dilution of precision
GNSS augmentation
Air navigation
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