Systematic Inconsistencies Between VLBI CRF and TRF Solutions Caused by Different Analysis Options

We assess the systematics between Very Long Baseline Interferometry (VLBI) terrestrial and celestial reference frames (TRF and CRF) solutions caused by different analysis options. Comparisons are achieved by sequential variation of options relative to a reference solution, which fulfills the requirements of the International VLBI Service for Geodesy and Astrometry (IVS) analysis coordination. Neglecting the total NASA/GSFC Data Assimilation Office (DAO) a priori gradients causes the largest effects: Mean source declinations differ up to 0.2mas, station positions are shifted southwards, and heights are systematically larger by up to 3mm, if no a priori gradients are applied. The effect is explained with the application of gradient constraints. Antenna thermal deformations, atmospheric pressure loading, and the atmosphere pressure used for hydrostatic delay modeling still exhibit significant effects on the TRF, but corresponding CRF differences (about 10μas) are insignificant. The application of NMF atmosphere mapping functions can systematically affect source declinations up to 30μas, which is between the estimated axes stability (10μas) and the mean positional accuracy (40μas) specified for the ICRF2. Further significant systematic effects are seasonal variations of the terrestrial network scale (±1mm) neglecting antenna thermal deformations, and seasonal variations of station positions, primarily of the vertical component up to 5mm, neglecting atmospheric loading. The application of NMF instead of VMF1 can result in differences of station heights up to 6mm, but no overall global systematic can be found. Using constant atmosphere pressure values for the determination of hydrostatic zenith delays systematically deforms the TRF: station height differences mostly show the same sign with absolute values exceeding 1mm.

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