Importance of the Hartebeesthoek radio astronomy observatory for the VLBI network

Abstract

This master thesis provides an insight into the only fundamental geodetic station in Africa, the Hartebeesthoek Radio Astronomy Observatory (HartRAO). In particular, the Very Long Baseline Interferometry (VLBI), one of the space geodetic techniques present at the site, is examined in detail. It's importance for the whole network of stations is evaluated on the basis of typical VLBI results, such as the International Celestial Reference Frame (ICRF), the International Terrestrial Reference Frame (ITRF) and Earth Orientation Parameters (EOP). In order to provide a prediction of the importance of the station in the past, two datasets with real data were used, namely the continuous VLBI campaign from 2008 (CONT08) and IVS-R1 sessions from the year 2011 and 2012. HartRAO's possible contribution to the future VLBI2010 Global Observing System (VGOS) network is investigated as well which was done using simulated data for different telescope types (a 15 m legacy antenna, a VGOS antenna or two VGOS antennas) at HartRAO. A VGOS network similar to the ones suggested in the literature is used. Simulations and schedules are created with the Vienna VLBI Software (VieVS). The results from the real data sets suggest that HartRAO was and is one of the most important stations for the VLBI network. Especially EOP estimation is heavily dependent on HartRAO due to it's remote location. This effect is very prominent in the real data sets, with a formal error increase of about 50% for nutation and 50% to 100% for polar motion when HartRAO is removed from the network. It can be seen in the simulated VGOS network as well but, since the stations are more evenly distributed, it is not that prominent. Nevertheless, HartRAO is still the most remote station of the network and, therefore, contributes significantly to the estimation of EOP, with the error of polar motion becoming 40% larger when comparing the VGOS network without HartRAO with the VGOS network with a twin telescope at Hartebeesthoek (HartTWIN). Furthermore, HartRAO is of significant importance for the estimation of sources; in particular, sources on the Southern Hemisphere depend heavily on the African telescope.