| dc.description.abstract | The African Very Long Baseline Interferometry, VLBI, Network (AVN) will be an African array of radio telescopes across Africa comprising of converted redundant satellite Earth-station antennas and new purpose-build radio antennas. The first one of these antennas, in Ghana, has already been converted into a radio telescope. In this study, the value that these African radio telescopes, and in particular the Kenyan telescope, will add to the AVN as well as to the existing global VLBI networks for astronomy, geodesy and astrometry was reviewed. The Radio Frequency Interference (RFI) was assessed based on population densities at different radii using the NASA Web Population Estimator and UNDP Population data report (2015), the telephone, mobile and internet subscriptions and the electricity connectivity using the ITU Report, 2015. The weather data was analyzed using NASA’s GEOSFIT to determine the atmospheric opacity at each AVN site for a period of three years, January 2013 to November 2015. The SCHED software was used to create U-V coverage plots of the AVN antennas plus the European VLBI Network (EVN) and the Australian Long Baseline Array (LBA) at different declinations. Earth Orientation parameters (EOPs), baseline length repeatabilities and source position estimates were scheduled, then simulated and analyzed through simulated geodetic and astrometric VLBI observations using the Vienna VLBI Software (VieVS). The AVN antennas were added to the International VLBI Service (IVS) geodetic session R1675 scheduled and then simulated to observe changes in the EOPs and Baseline length repeatabilities. The AVN antennas in the south of the equator (AVN1) were added to the IVS Celestial Reference for Deep South (CRDS) session to observe changes in the source positions.
The population densities around the Kenyan site is 70, 78 and 175 people/km2 at 5, 10 and 20 km radii while for Ghana is 1175, 981 and 1560 people/km2 at the same radii. This is compared to population densities of 24, 25 and 79 people/km2 at the same radii at the South African site. The mean atmospheric opacity for the Kenyan site is 0.36, 0.12 and 0.32 at 22, 43 and 100 GHz, whereas for the Ghanian site is 0.50, 0.21 and 0.67 at the same frequencies. HartRAO has values of 0.28, 0.10 and 0.20 at the same frequencies. At x-band, the AVN antennas improve the u-v coverage of the LBA from 7% to 23% at the declination of -10º and from 12% to 36% at a declination of -90º, while improving the u-v coverage for the EVN from 6.47% to 28.76% at declination of 0º and from 47.23% to 73.29% at 80º along the short baselines. For the EOPS, the error in polar motion was reduced from 51.35 μas in R1675 to 24.81 μas in R1675+AVN. As for the source position estimates, the Kenyan antenna adds the most to the CRDS by reducing the errors in the right ascension from 0.345 to 0.240 ms and in declination from 0.557 to 0.351 mas.
The AVN will greatly impact the global VLBI networks by improving the u-v coverage, increasing the accuracy of the EOPs and source positions, have favorable atmospheric conditions for high frequencies observations although measures must be put into place earlier to mitigate RFI. | en_US |
