Impact of network geometry, observation schemes and telescope structure deformations on local ties: simulations applied to Sardinia Radio Telescope |
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| Authors: | Claudio Abbondanza Pierguido Sarti |
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| Institution: | (1) Istituto di Radioastronomia (IRA)-Istituto Nazionale di Astrofisica (INAF), Via P. Gobetti, 101, 40129 Bologna, Italy;(2) Present address: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA |
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| Abstract: | The 64-m Sardinia Radio Telescope (SRT) is currently under construction in Sardinia (Italy). To ensure future surveying and
monitoring operations at an utmost level of accuracy, we aim at selecting the optimal design and the most cost-effective solution
for the establishment of the local ground control network (LGCN). We simulate and test 45 data sets corresponding to 5 different
network configurations. We investigate the influence of 2 LGCN geometries (14 or 8 ground markers) and 3 terrestrial observation
schemes (based on redundant forward intersections or side shots) on the precision and accuracy of the conventional reference
point (CRP) of SRT and the simulated tie vector with a global navigation satellite system (GNSS) station. In addition, thermal
and gravitational deformations of the radio telescope structure are simulated as systematic errors introduced into the observations
and their effects on the CRP estimates are quantified. The state-of-the-art of CRP surveying and computation, based on terrestrial
indirect methods, is applied. We show how terrestrial indirect methods can estimate the position of the radio telescope CRP
to the millimeter precision level. With our simulations, we prove that limiting the LGCN to a 8-point configuration ensures
the same precision on the CRP obtained with a 14-point network. Furthermore, we demonstrate that in the absence of telescope
deformations, side shots, despite the lower redundancy, preserve a precision similar to that of redundant forward intersections.
We show that the deformations due to gravitational flexure and thermal expansion of the radio telescope cannot be neglected
in the tie vector computation, since they may bias the CRP estimate by several millimeters degrading its accuracy but not
impacting on its formal precision. We highlight the dependency of the correlation matrices of the solutions on the geometry
of the network and the observation schemes. Similarly, varying the extent of telescope deformations, we show that the CRP
estimate again depends on the combination of the network geometry and the observation schemes. |
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