Investigating the VLBI Scale Behaviour. How is the VLBI Technique Defined Scale Affected by the Session Network Components?
Examensarbete för masterexamen
Wireless, photonics and space engineering (MPWPS), MSc
Nyström Lindé, Fredrik
In preparation of the latest realisation of the International Terrestrial Reference Frame (ITRF), the ITRF2020, the Very Long Baseline Interferometry (VLBI) so lution displayed some strange behaviour in regards to its scale factor. Some clear reason for what can only be described as a scale drift, has yet to be observed, while several possible reasons have been discussed. In this thesis we aim to investigate the VLBI scale factor based on the Onsala Space Observatory (OSO) individual VLBI solution to find any obvious correlation between the scale drift and the components of a VLBI session network. A large portion of the work was spent developing a toolbox in MATLAB to analyse VLBI solutions, and to estimate the seven Helmert parameters for transformation between different terrestrial reference frames (TRFs). With these tools we looked at the effects of simulating an erroneous uplift model by artificially adding motion to stations distributed around the globe. The results indicated that the necessary uplift error to cause such a drift would have to be in the magnitude of cm/yr. Then we also used the software package ASCOT to repro cess global VLBI solutions while excluding stations that had experienced different technical issues, or on the hypothesis that network volume or distribution would have an effect. The results of excluding stations with technical issues proved most promising in reducing the scale drift, while removing stations based on the network distribution seemed to have the opposite effect. Our results indicate that the VLBI scale drift problem seem to be the result of a combination of factors, and there are surely other aspects at play as well.
VLBI, IVS, ITRF, scale factor, OSO, space geodesy, Helmert parameters