Dilution of Precision (DOP) factors for evaluating observations to Galileo satellites with VLBI

Abstract

Observing satellites besides natural extra-galactic radio sources (quasars) with Very Long Baseline Interferometry (VLBI) telescopes permits the extension of the current research of this interferometric technique. These observations offer a variety of new applications such as the direct determination of the absolute orientation of the satellite constellation with respect to the International Celestial Reference Frame (ICRF). In addition, observing satellites with VLBI telescopes enables high precision tying of space geodetic techniques and therefore results in improvement of long-term reference frames. In order to observe quasars and geodetic satellites with the same instruments it is necessary that satellites transmit signals that can be observed by VLBI telescopes. Therefore, ideas of installing a dedicated VLBI transmitter on board of future Galileo satellites have been proposed over the last years. The following contribution provides an evaluation study of observations to Galileo satellites with VLBI telescopes. Recently, the scheduling software VieSched++ was equipped with a newly developed satellite scheduling module, which is used for the determination of possible observation periods to Galileo satellites from a selected VLBI network. These possible observations are evaluated through their sensitivity towards changes of the satellite position concerning the radial, along-track and cross-track component. The sensitivities of an observation towards changes in the respective components are indicated by different Dilution of Precision (DOP) factors, which are the radial DOP, the along-track DOP and the cross-track DOP. The lower the value of the respective DOP the more sensitive the observation is towards the corresponding component.