Comparison of VLBI and GNSS common view for time transfer

Abstract

With the rapid development of optical clock, the stability and system uncertainty of optical clocks has reached a 1.0e–18 level. Optical clocks will likely constitute the next generation of time-frequency standards for redefining the SI second. Because time and frequency transfer services that rely on satellite systems are not always reliable and currently available technologies are insufficient for comparing the next generation of frequency standards, high-precision time and transfer techniques are strongly desired. Very Long Baseline Interferometry (VLBI) is one of the space geodetic techniques that measure the arrival time delays between multiple stations utilizing radio signals from distant celestial radio sources. Not only can VLBI obtain the angle position measurement of the radio source with sub-millisecond accuracy and the station coordinate measurement with millimeter accuracy, but also, it can provide high-precision information regarding inter-station atomic clock differences. Therefore, it is theoretically feasible to use the VLBI technology to do the remote time transfer. Because of this characteristic of VLBI technology, VLBI has significant application potential in the field of remote time transfer. To confirm the suitability of VLBI to time-frequency transfer for future practical applications, the results of VLBI and GPS common view time transfer were compared using a Kunming-Urumqi baseline. The performance characteristics of time transfer based on VLBI are then analyzed. Experimental results show that VLBI technology can accurately measure the variation of clock differences between stations as same as the GPS common view time comparison technology. It briefly describes the challenges of future VLBI technology for practical applications of time transfer.

Time transfer and significance of vertical land motion in relativistic geodesy applications: a review paper

“…The time delay is affected by the offset of the reference clocks in each observatory, the cable instrumental delay, and the tropospheric and ionospheric atmosphere propagation delays (cf. Ma et al, 1986;Wang et al, 2019). For example, the delay due to the ionospheric effect can be reduced using different frequencies similar to the GNSS precise positioning methods.…”

“…Hence, the VLBI technique can be used for time transfer and relativistic geodesy applications (cf. Wang et al, 2019;Haas, 2020).…”

“…Allan and Weiss, 1980). The stability of the VLBI frequency link between the station clocks has been studied in different projects, e.g., by Rieck et al (2010a) in Onsala Space Observatory in Sweden, Wang et al (2019) in Kunming-Urumqi baseline in China, and Pizzocaro et al (2020) in Italy and Japan (see also Bouman, 2012). The later study proposes using dedicated transportable VLBI stations and taking advantage of node-hub style observations.…”