Title: Combined observations of GNSS and astronomical sources: Can you see both world's through a single lens?
Presenting Author: Johnathan York
Organization: Applied Research Laboratories, The University of Texas at Austin
Co-Author(s): David Munton, Zach Prihoda, Connor Brashar

Abstract:
We begin with the question: "Is it possible to develop an instrument concept in which GNSS signals and astronomical source signals are sampled via the same signal chain, effectively ensuring that both measurements are made from the same antenna phase center, when processed in conjunction with measurements from a VLBI-like antenna?" The low gain of the standard GNSS antennas, and the limited frequency range over which they operate, would seem to make this an unlikely concept. However, there would be advantages to being able to provide a common signal chain for both, effectively providing a unification of geodetically important measurements at the instrument level. For example, one geodetic application that can be explored is whether the determination of UT1-UTC can be made from such observations. We will describe our efforts to observe bright celestial sources through a combination of a dish antenna and a low gain GNSS antenna using low-cost rubidium frequency standards. Our focus will be on the difficulties that arise in attempting this type of measurement. In our system, one of the specific problems that arises is an incoherency between measurements as a result of the stability of the oscillators in use. This stability limits our ability to deeply integrate. We will describe how our unconventional measurements allow us to extract an estimate of the clock behavior from GNSS signals, and to extend the period in which we can integrate coherently.